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Unmanned Spaceflight.com _ Mars _ Welcome Professor "brine splat" Burt

Posted by: centsworth_II Jun 15 2007, 08:37 PM

QUOTE (dburt @ Jun 14 2007, 11:04 PM) *
As an aside, the related suggestion that at least some of the fine-grained layers above or below any boulder
deposits (or elsewhere on Mars) could likewise represent ancient impact deposits (non-ballistic fine-grained
sand and dust distributed over vast areas by fast-moving, turbulent, erosive gaseous density currents - a.k.a.
impact surge clouds - or by the winds as later fallout) already seems to have aroused considerable controversy
on this forum, but again that's peripheral to Emily's boulder comment.


So you're the dburt of Basal Surge fame?

"ASU geologists L. Paul Knauth and Donald Burt, who along with Kenneth Wohletz of Los Alamos National
Laboratory, say that base surges resulting from massive explosions caused by meteorite strikes offer a simpler
and more consistent explanation for the rock formations and sediment layers found at the Opportunity site.
"
http://www.asu.edu/news/stories/200512/20051222_mars_meteorites.htm

I haven't followed the situation closely enough to ask any good questions, but I wonder if anyone else here
would like to ask about your current views.

for reference, the basal surge thread is here:
http://www.unmannedspaceflight.com/index.php?showtopic=2438&hl=surge&st=30

Posted by: dburt Jun 16 2007, 02:11 AM

Yes, guilty as charged - that "brine splat" Burt. As someone who, like many of you, is addicted to looking at the downloaded MER images almost daily (vicarious field work on another planet), I've long admired the inspired image processing that many on this site carry out, and was overcome with admiration a few days ago when I observed how rapidly everyone zoomed in on problems inherent in news stories about puddles on the face of "Burns Cliff". So I thought I should finally stop lurking and log in to give anyone who wishes a chance to ask questions about or raise objections to our published ideas on Mars impacts, and their hypothetical relation to observations at the two rover sites. (And yes, I'm well aware that some here have enthusiastically and at length found fault with these ideas already, in the thread that was cited and quite a few others. As a life-long professor, it's my job to be grateful for and encourage such enthusiasm, even if I'm secretly grinding my teeth.)

BTW, I'm pretty sure that this particular thread is not the best place for such a discussion. So if anyone has a general question or comment please feel free start a new thread, perhaps in the "Mars general" area (if only to liven things up a bit while we're all waiting for Oppy to enter Victoria).

--Don

Posted by: nprev Jun 16 2007, 06:51 AM

Professor Burt, let me say merely that I am glad you are here--it's a good place, in all senses of the word! --and that, as a layperson, I greatly admire your intellectual honesty.

Cannot speak for admin policies of course re topic placement, but it seems quite safe to say that your opinions and contributions will be welcomed by all and may often encourage provocative, often quite enlightening comments...that is the hallmark of UMSF.com. (Not running the circus, here--that's poor Doug's job--I'm just one of the clowns! Welcome, welcome, sir! smile.gif )

Posted by: centsworth_II Jun 16 2007, 03:08 PM

QUOTE (nprev @ Jun 16 2007, 02:51 AM) *
Professor Burt, let me say merely that I am glad you are here--


Thanks, nprev, for putting out the welcome mat.
[EDIT -EGD]

Posted by: Bill Harris Jun 16 2007, 05:58 PM

Welcome to Mars, Prof Burt. Here are a couple of my favorite 'local' discussions on basal surge/brine splat:

http://www.unmannedspaceflight.com/index.php?showtopic=1584

http://www.unmannedspaceflight.com/index.php?showtopic=2438

http://www.unmannedspaceflight.com/index.php?showtopic=1884

http://www.unmannedspaceflight.com/index.php?showtopic=3060

--Bill

Posted by: dburt Jun 17 2007, 08:12 AM

Thanks much for the warm welcome. Am I now supposed to feel like an innocent sheep being fattened for slaughter? (Are those knives I hear being sharpened in the kitchen?) biggrin.gif In any case, thanks also for the brief compendium of relevant threads, some of which were old enough that I hadn't read them previously. In addition, here's a more recent thread in which a few correspondents dumped on my "mine dump" article from Eos last December:

http://www.unmannedspaceflight.com/index.php?showtopic=3643

Rather than trying to respond at length to all of the comments in these threads, I'd much prefer to make brief replies to specific points or queries. Otherwise, I may start pontificating at random, like I sometimes do in class, and that could get really boring.

Here's a warning sample: Along with many of you, I'm a firm believer in Carl Sagan's famous dictum applied to Mars, that "Extraordinary claims require extraordinary proof." So far we haven't seen that proof for most aspects of Meridiani or Gusev geology. As an example, it would be premature for me to call those enigmatic spherules "impact spherules" (not the same as tektites, BTW, because tektites are not vapor condensates like spherules, but rather are oddly shaped splash droplets) or "accretionary lapilli" or even "hematite hailstones". Of course, it is just as premature for far too many writers to baldly refer to them as "concretions" (some amateurs regard them as biological products, yet another hypothesis). "Spherules" just describes their obvious spherical shape, and "blueberries" and "BB's" describe their uniformly tiny size, without genetic connotations. For this example alone, we have at least three competing hypotheses, but so far none of them has advanced to being a theory (recall that evolution is a theory, as is plate tectonics, and even gravity). In this regard, any valid scientific hypothesis is testable, usually via making various predictions; it can become a theory only after the competing hypotheses fail their tests. Until now I haven't seen any testable predictions made as part of the MER team's remarkably complex and elegant Meridiani hypotheses, so perhaps they feel these predictions should be obvious. Nevertheless, I'd prefer to see them spelled out explicitly.

Here's another: I'm also a firm believer in Occam's razor, which (as reportedly reworded by Einstein) states that the best hypothesis is the simplest one that accounts for all the observations. Although none of us are experts on impacts (Wohletz probably comes closest, through his experience with bomb tests and exploding volcanoes), my co-authors and I settled on the impact hypothesis via the process of elimination - it seemed the simplest one that could account for all of the rover and orbital observations, and it was obviously testable. The hypothesis in one word: Boom! (Is that simple enough?) More complex: Boom, boom, boom, boom... (= multiple impacts). Well - now you've been warned about Herr Doktor Professor. Please stop me before I stick out my gut and begin to pontificate again...

--Don

Posted by: djellison Jun 17 2007, 08:45 AM

Trying to play devils advocate here - how does that tie in with the fact that heading south (up section) the spherules got smaller and smaller and almost dissappeared - and then reappeared in huge quantities on the Victoria annulus?

And to be fair - the MER team have not gone "here are concretions - bingo - water" - there are more slices to the evidence pie than that ( Jarosite, Vugs, Sulphates predicted by Burns, Small scale cross bedding)

If you go to a place with an extensive prediction ready to test - then surely you're going to be prone to a biased interpretation of what happened? Alternatively - what obvious tests do you have in mind?

Doug
(Not a geologist, just playing devils advocate smile.gif )

Posted by: Bill Harris Jun 17 2007, 11:25 AM

No one really dumpes on the mine dump hypothesis; in my experience, anytime you find sulfates you need to look for sulfides.

Thedownside to the brine spalt/base surge hypotheis is that it tends to get rolled out as a universal, all-encompassing explanation for Meridiani, whereas there are clearly many interactive processes going on there.

--Bill

Posted by: nprev Jun 17 2007, 01:49 PM

My working hypothesis re blueberry size has been duration of immersion: the longer they were in solution, the bigger they got. What would be interesting to know is the rate at which these things grew (assuming of course here that they are in fact concretions).

As a kid, I saw copper sulfate accretions (asymmetrical) develop in wet spots on mine tailings in Butte, MT over the course of a year or two, some becoming quite large--2-3 cm across on their longest dimensions. I don't know if iron-based minerals can do this as quickly, but if so then this may argue that Merdiani's blueberries might not have required long-term immersion to form.

Posted by: dvandorn Jun 17 2007, 03:28 PM

QUOTE (dburt @ Jun 17 2007, 03:12 AM) *
...recall that evolution is a theory, as is plate tectonics, and even gravity.

I respectfully disagree with this statement. The processes are proven. Some of the mechanisms by which these processes function are not proven, and are therefore theoretical. (I have the same argument with my girlfriend... smile.gif)

QUOTE (dburt @ Jun 17 2007, 03:12 AM) *
...recall that evolution is a theory, as is ...my co-authors and I settled on the impact hypothesis via the process of elimination - it seemed the simplest one that could account for all of the rover and orbital observations, and it was obviously testable. The hypothesis in one word: Boom! (Is that simple enough?) More complex: Boom, boom, boom, boom... (= multiple impacts).

Now, here is where you get closer to some of the mechanisms than many others, I think. While I truly believe that the Merdiani landforms and minerology were formed by groundwater and standing water (among other things), we have to be aware that impacts have modified the Martian surface far more than they have modified Earth. Impact is a primary agent in much planetary surface formation, and I agree that when you invoke Occam's Razor, the first thing you need to look at are impact processes.

QUOTE (dburt @ Jun 17 2007, 03:12 AM) *
...recall that evolution is a theory, as is Well - now you've been warned about Herr Doktor Professor. Please stop me before I stick out my gut and begin to pontificate again...

Hey -- as long as you don't mind our honest responses (and you don't start wearing tin-foil hats), we *love* pontification around here! Please, keep it up. Or, paraphrasing what someone once said, I may not agree with all of your hypotheses, but I defend to the death your right to express them...

-the other Doug

Posted by: centsworth_II Jun 17 2007, 05:31 PM

As an interested, but not knowledgeable, observer, I'm struck this way:

I've been shown the small scale evidence that djellison mentioned that indicates
water based processes and I've seen the larger scale layer formations that I'm told
represent wind deposition. In both cases I nod my head and think "yes, I can see that."

Now a third process -- impact -- has been brought to my attention and it occurs to me
that apart from the obvious -- the actual hole in the ground, the rim, and ejecta apron,
I haven't thought about what the results of impact base surge would look like in a
cross section of the Martian surface.

The combinations of processes (and throw in volcanism) that formed the Meridian layering
could get very complex in spite of attempts to use Occam's razor. I suppose that even
assuming that the berries and vugs were formed in water, does not eliminate the possibility
that the layers themselves were initially placed by means other than wind or water.

Posted by: dburt Jun 18 2007, 12:00 PM

Wow, it was feast or famine, and now's the feast - I'll try to reply briefly (and shall of course fail, being a professor), in order. First to Doug: Thank you. I love devil's advocates - a favorite teaching role. That spherule size would vary with position in the section, and that many beds would be free of spherules, strikes me as just as consistent with the impact/vapor condensation hypothesis as with the concretion hypothesis. That deep spherules would be dug up and homogeneously redistributed around a small impact crater (Victoria) speaks for itself regarding the importance of impacts.

What we want is observations and predictions that might help differentiate one hypothesis from the other. What the impact hypothesis predicts is that impact spherules of various types (e.g., glassy, possibly metallic if from a metallic impactor, possibly sulfidic if the target was sulfidic, various accretionary lapilli) should be extremely widespread on Mars (given how heavily cratered it is), and that their specific composition and size might depend on the composition and energetics (size, velocity) of the impactor, and, more importantly, on the composition (including ice or brine content) and mechanical nature (e.g., hard rock, very soft rock) of the target area. (The surge cloud can also pick up dust and sand and possibly larger rock fragments - ordinary lapilli - by scouring along its path; scouring forms cross-bedding.) So far only two landers with microscopic imagers have landed on Mars - and both have found tiny, nearly perfect spherules in cross-bedded, salty, sandy rock (more homogeneously distributed at Meridiani than at Gusev's Home Plate). The impact hypothesis would predict that any future rovers with MI's landing in similar layered terrains should be able to find similar spherules, and perhaps that spherules should litter the surface everywhere. Most spherules would be at least as small as ordinary sand grains, in which case they could be mixed (diluted) with normal basaltic sand and moved along by the wind. Comparatively large, dense (hematitic) spherules, like those at Meridiani and probably other areas, would be left behind as a wind-resistant lag (spherule pavement or armor) after wind removal of fines. So far predictions of the impact hypothesis seem okay - tiny spherules at both Gusev and Meridiani, and probably all over the place. Current instrumentation is not able to detect the impact-formed high pressure minerals, melts, and microtextures that should likewise be widespread. Craters, the best evidence of impacts, are everywhere of course.

That brings us to predictions concerning spherule size, shape, clumping, and distribution in the rock. I note that I am partly rehashing my 2007 LPSC abstract so far, so I'll just refer you to that for the detailed arguments:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1922.pdf

The impact hypothesis passes with an "A" and the concretion hypothesis fails, as far as I can tell, even considering the Navajo Sandstone and similar rocks of uniform porosity and permeability. Ditto regarding the distinctive Ni enrichment detected in spherules at the "berry bowl" and elsewhere (nickel enrichment, along with enrichment in iridium and other platinum group elements, characterizes fully oxidized impact spherules related to the impact assumed to have killed the dinosaurs 65 million years ago). How alleged sedimentary concretions got to contain relatively coarse, shiny "gray hematite" (so-called specular hematite, the high temperature hydrothermal kind) has never been properly addressed by the concretion crowd, as far as I know. High temperature formation of specular hematite is obviously no problem during a steamy impact. And so on. If the MER team wants to convince me that Oppy has found concretions, in terms of size they'd have to show me some that are far too big or too massively clumped together for a turbulent cloud to support (not simple doublets and triplets, which are easily explained by surface stickiness). In terms of shape, they'd have to show me some that are irregular shapes, flattened by vertical permeability variations in the rock, or elongated by fluid flow (look in any freshman textbook for typical concretion shapes and sizes). In terms of distribution, they'd have to show me variations that obviously depend on fluid flow, and on mixing of different brines that were oxidized and reduced, or concentrated and dilute (e.g., spherules should concentrate just below the paleo water table, or along fractures or veins, or beside brine mixing surfaces that cut bedding). So far, nothing like that has been imaged, whereas you see such features everywhere in the Navajo Sandstone (an alleged analog).

With regard to your comment on possibly biased interpretations, I'll let "follow the water" speak for itself. Recall that prior to the rover landing Meridiani was first supposed to be the largest hot spring in the solar system, and then the largest lake-deposited metamorphosed sedimentary iron formation. Expectations of finding evidence for a lake was why they landed there (and at Gusev). Subconsciously, they weren't going to give up that lake idea too easily, I would guess (just dry it up, blow it around, soak it, erode it down to the water table, blow it around some more, uniformly mix different-density brines in it without dissolving or recrystallizing soluble salts, erode it down to the water table again, and make fairly deep water flow across it locally without carving channels, although I admit I do get confused over the exact order of events, and I may have left something out). We started out with no prior expectations, but to us the images as they came down each day simply did not show what was claimed at the initial news conference and afterwards in meeting presentations and refereed publications. Examples: Why were the alleged concretions all so perfectly spherical, and all so uniformly tiny? Why were the alleged water-soaked evaporites a uniform mixture of highly soluble and nearly insoluble sulfate salts? Where were the large salt crystals and bulk impermeability that one would expect from water soaking? Where were the shales that could indentify a playa lake or smaller interdune puddle? Where did most of the chlorides go? Do hematitic concretions even occur in evaporites? Why do almost all terrestrial analogs for alleged atmospheric acids ultimately depend on weathering of pyrite - fool's gold - or other sulfides in mineral deposits or districts like Rio Tinto, Spain? If there was flowing surficial water, why weren't there also visible channels or braided stream patterns or mud cracks? And similar questions by the hundreds, only some of which were answered by the elegant and highly complex genetic models that the MER team evolved (these interpretational models and hypotheses were erroneously referred to as "discoveries"). These interpretations, BTW, seem only to apply to a rare set of circumstances that occurred only at Meridiani, and so their predictive power is limited. The team chose to apply a completely different interpretation to almost identical-appearing rocks at Home Plate and vicinity, despite the cross-bedded sands, acid salts, and spherules. In place of the hypothetical enormous "vanished playa" of Meridiani, they hypothesized a little "vanished volcano". Why not notice the impact craters that are so highly visible all over the place, and that all the rocks are fragmental (bashed near to death)? Why not notice that MOC and then HiRise imaging make it appear that similar-looking cross-bedded, salty rocks occur all over the place, not just at the two landing sites? (Pardon my little rant.)

With regard to impacts, please don't confuse our impact hypothesis with the "white Mars" hypothesis of Nick Hoffman. They're not the same. That said, Nick's a very intelligent, well-read guy, and I'd hate to take him on in a technical discussion of outflow channels. A lot of what he thinks about Mars in general I now agree with, and he said it first. Unlike him, however, my co-authors and I see no reason to exclude geologically fleeting occurrences of liquid water (brine) in ancient outflow channels and seas at lower elevations, or in temporary streams and crater lakes (like Gusev) at higher elevations, or in young gullies. Such waters, unless they were a concentrated Ca-enriched chloride brine (or concentrated sulfuric acid, unlikely for other reasons), were probably freezing over and then sublimating furiously (as so beautifully described in the original "Red Mars" novel by Kim Stanley Robinson). Our own "white Mars" model (with apologies to both Hoffman and Robinson), might then consist of lots of buried water ice above chloride-enriched brines and/or white crystalline salts, and Knauth and I published a couple of papers to that effect in 2002 and 2003 (inspired by the young gully phenomenon). You didn't specifically ask about salts I realize, although you did mention hydrous sulfates and empty crystal cavities. We covered those in our original Nature paper in 2005. No more moisture is required than would be present in the original surge cloud (mainly condensing steam) or could later be removed from the atmosphere by water-attracting (hygroscopic or deliquescent) salts. For us the rovers have imaged absolutely no unambiguous surface evidence for large quantities of standing or flowing liquid water (brine) at either landing site (including ground water or spring water). We don't a priori exclude evidence for liquids anywhere else, especially in rocks older than those now exposed at the surface of the two landing sites (i.e., you could drill a deep hole at either landing site and possibly find the desired evidence beneath the impact beds, if that's what they are).

Well, that's way too long, as predicted, but then Doug is the boss here and presumably merits a detailed discourse. I'll have to address other people's questions and concerns later (sorry). Let me close with a naive question: A week ago, in this forum's probably greatest triumph to date, many of you questioned the ability of liquid water in the form of a puddle to exist on the 20 degree slope of Burns Cliff. What do you think about the ability of bottom-fed surficial water to flow vigorously across a perfectly horizontal surface (allegedly made horizontal by wind erosion of sand down to the water table) while trapped in localized interdune depressions not connected to each other by any visible flow channels? That's what seems to be required by the highly localized "festoon" hypothesis of one member of the MER team, unless I have his argument for the rarity of "festoons" completely wrong (which is certainly possible - he loves to cloak what he is saying in obscure geojargon like "festoon"). Is flowing water any more likely in an isolated horizontal basin (where I'd expect a puddle) than puddles are on a slope? Or am I overlooking something important that's obvious to everyone else? Note that I didn't say such flow was flat-out impossible - there could be a slight slope and the sands could be extraordinarily permeable - it just seems unlikely and unsatisfying (like so much of the rest of the complex Meridiani scenario).

Finally, I am writing this rant at home on Father's Day, and am certainly not speaking for my employer, my co-authors (who have not seen this), or my more plantetological colleagues. And I'm not a lawyer, so please forgive me if I have unintentionally offended anyone. And evolution, plate tectonics, and gravity are all still "theories" (in science, that's as good as it gets - there is no infallible source of wisdom, we all make mistakes, and any theory is always subject to modification by new observations. For example, I wish we understood gravity better, so I could go study Mars instead of just Antarctica and the Peruvian/Bolivian altiplano.)

--Don

Posted by: centsworth_II Jun 18 2007, 02:54 PM

QUOTE (dburt @ Jun 18 2007, 08:00 AM) *
Let me close with a naive question: ....What do you think about the ability of bottom-fed
surficial water to flow vigorously across a perfectly horizontal surface (allegedly made
horizontal by wind erosion of sand down to the water table) while trapped in localized
interdune depressions not connected to each other by any visible flow channels?

A naive response: I wonder what water flow velocity would be required to form the smiley
festoons seen in Eagle crater. Could they be formed by wind-blown waves on a thin layer
of water? What about flow over an ever so slightly sloped terrain. What slope would be
required? Would the slopes Opportunity has traversed to date be sufficient? What about
tidal flow of shallow water? I haven't read enough to know if he exact physics of what
flow rates would be required or how they could have been achieved has been addressed.


Edit: I don't see why the surface would be necessarily be "perfectly horizontal"
as stated in the "naive question". The surface is not perfectly horizontal today.

Edit 2: Ah, "wind erosion of sand down to the water table". But the water table
could recede, allowing a sloped surface to form, then rise again expelling water
onto the sloped surface. Over thousands of years of course. (Or maybe less.)

Edit 3: Tides!?! (That's really naive!)

Posted by: nprev Jun 18 2007, 04:29 PM

I'll echo $0.02's naive response with one of my own: We're not completely sure of detailed surface morphology or even inclination with respect to local Mars-normal during the purported 'wet' era, whenever that might have been. This uncertainty alone means that framing arguments re surface flow velocity (or even feasibility) based on current observations may be premature.

Meridiani is certainly quite static and flat now, but this may not have been the case throughout its entire history (not talking mountains here, but it's certainly possible that the area was tilted with respect to local vertical in some way at some point, possibly numerous times and especially during the Tharsis uplift event which disrupted the entire equilibrium of the planet).

EDIT: "I'll try to reply briefly (and shall of course fail, being a professor)"... biggrin.gif ...please don't worry about that, we love it!

Posted by: centsworth_II Jun 18 2007, 04:47 PM

I imagine something like this, with changes in the water table adjusting the area
and extent of the water/land interface over large areas. Tides are out I guess (duh!!!).
Are these changes, plus wind-induced waves capable of forming the festoons?


http://news.thomasnet.com/IMT/archives/2006/07/just_another_case_sinkhole_drying_entire_florida_lake_engineers.html?t=archive

Posted by: nprev Jun 18 2007, 05:01 PM

I don't know if tides could be considered as part of the issue at this point, $0.02. We don't know what the possible depth & volume of any waters @ Meridiani might have been, and of course the only significant tidal influence would be solar...difficult to reconstruct a plausible scenario with the limited data we have.

Posted by: dvandorn Jun 18 2007, 05:17 PM

Not to belabor a point, but it gets down to how you exercise the scientific process.

Gravitation, terrestrial crustal movement and even diversification and radiation of species are not theoretical, they are observed phenomenah. They are objectively, empirically observable. The mechanisms involved in how they operate are theoretical. (This is the argument I get into with my girlfriend... smile.gif )

You cannot open your assumptions so broadly that you begin to treat empirical observations as unproven theories. That sabotages the scientific process and leads to festoons of tin-foil hats... smile.gif

-the other Doug

Posted by: centsworth_II Jun 18 2007, 06:08 PM

QUOTE (dvandorn @ Jun 18 2007, 01:17 PM) *
You cannot open your assumptions so broadly that you begin to treat
empirical observations as unproven theories.

The festoons are "objectively, empirically observable". The "mechanisms
involved" in how they form are theoretical. I don't think anyone is arguing those
points. I'm curious about what theories are out there concerning how the water
flow (that caused the festoons according to the water flow formation theory)
occurred. Wind? Rising and falling water tables on a slope? Maybe it is no
problem for wind blowing over shallow water to form such festoons. I don't know.

Posted by: nprev Jun 18 2007, 06:22 PM

QUOTE (centsworth_II @ Jun 18 2007, 11:08 AM) *
The festoons are "objectively, empirically observable". The "mechanisms
involved in how they form are theoretical... Maybe it is no
problem for wind blowing over shallow water to form such festoons. I don't know.


Yep; there's the real rub: too many undefined variables, and therefore poor constraints on the scope of the problem. We don't know what the conditions were like, and one hell of a lot of legwork is needed to figure that out before even attempting to declare likely explanations for the observations. It does seem as if water was present at some point, but there seems to be precious little objective data that tells us for how long, or how often.

Posted by: stevo Jun 18 2007, 06:53 PM

QUOTE (dvandorn @ Jun 18 2007, 11:17 AM) *
Not to belabor a point, but it gets down to how you exercise the scientific process.

Gravitation, terrestrial crustal movement and even diversification and radiation of species are not theoretical, they are observed phenomenah.


No, they are not. The motion of planets, apples and bits of the Earth's surface are observations, the theories which account for them are theories. Hugely successful, taken as reality (or the best available description of it) in the normal course of science, but still theories. And necessarily open to falsification.

It seems to me that we need to keep this distinction very clear when we are observing a new world where the basic rules of chemistry and physics remain the same, but the situations are different from what we have previously seen on Earth.

Stevo

Posted by: dburt Jun 19 2007, 02:19 AM

Thanks for all the thoughtful replies about water flowing over a horizontal surface, in relation to "festoons". I agree such flow is theoretically possible, just not highly plausible (e.g., why don't you see "festoons" everywhere, across the entire area, if there was sheet flow, with no channels?). I'm reminded of the one about the procrastinating student who tells me he wants to take a make-up test because his grandmother died on the date of the first test and I say fine. Then he tells me the same thing again for the second test, and I think, well, okay, but that's kind of a coincidence. This kid is sure hard on grandmas, and he's all out. Then he comes up to me well after the third test and asks for a third make-up, "because my grandmother died". I say, hey wait a minute, you only had two, and he tells me something like, "well, my grandfather had a sex change operation" or "my father's mom was adopted, so she actually had two different mothers" or "my mom's mom was married to another woman, and my mom was fathered by an anonymous sperm donor" or "my father's family got divorced and remarried an awful lot, so I currently have 10 grandmothers". I think, well that's all theoretically possible, so I have to give him the makeup exam, but is it at all plausible? That's how we came to feel about the coincidences involved in the highly convoluted Meridiani story. Plus it doesn't explain how to form nearly identical-appearing, cross-bedded, sandy, salty, spherule-bearing rocks at Home Plate or anywhere else on Mars.

Making rare little "festoons" or trough-shaped current ripple cross-beds by the odd little eddy or vortex in a turbulent impact surge cloud seems far simpler conceptually. Such small trough shapes do occur in volcanic surge deposits - see figure and discussion in Knauth's 2007 LPSC abstract here:

http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1757.pdf

Actually, to a field geologist who habitually visualizes things in 3-D, most of the alleged Meridiani "festoons" appear to represent a topographic misinterpretation of a low-angle cross-bedded rock as viewed from above - see figure and discussion here:

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1869.pdf

Geologists sometimes call this effect "V-ing upstream". (When viewed from above, the horizontal bedding planes appear to bend up each crack and wrap around each ridge, like contour lines on a topographic map. Think of a person wearing horizontally striped pants, with you looking down at their rump from 5-feet up. The horizontal stripes will look like little troughs: UU.) The 5-foot high rover cameras can't bend down the way a real geologist could, to view the flat-lying beds from the side. Perhaps some of the 3-D image-processing gurus here at UMSF would like to take a stab at the rover "festoon" images to see if we're right or wrong about what look like troughs, but perhaps really aren't. (In other words, I'm asking for your help in discovering and visualizing the truth.)

Whatever the results of that important test, there would still be an awful lot of dead grandmothers at Meridiani, if you ask me.

BTW, the processes involved in forming impact surge deposits will probably never be as well studied or understood as those for deposition by wind and water. You can't confine a nuclear bomb to a wind tunnel, or to a tilted flume channel. If you want to observe surge deposition up close, you're dead, just like all those alleged grandmas. In the case of terrestrial impacts, fine-grained deposits begin to erode as soon as they're formed, and they're quickly gone. The extremely slow rate of wind erosion on Mars means that fine-grained impact deposits have a much better chance of being buried (and thus preserved) by later geological processes, such as more impacts. That preservation perhaps occurred at Meridiani and Home Plate, if we are correct.

--Don

Posted by: dvandorn Jun 19 2007, 02:40 AM

There is much more data to collect before any theory is proven. I really do appreciate your efforts, Professor. And I surely understand the difficulty in direct observation of large impact events. Even if you eventually are proven wrong, we will always need people to challenge the conventional wisdom, or else misinterpretations will never get addressed!

Thanks again for joining this forum.

-the other Doug

Posted by: ElkGroveDan Jun 19 2007, 02:42 AM

QUOTE (dburt @ Jun 18 2007, 06:19 PM) *
why don't you see "festoons" everywhere, across the entire area, if there was sheet flow, with no channels?)

Come on Don, now you're an educated guy. That's a bit like asking why paleontologists don't see fossils all over the Earth considering the widespread history of life here. After billions of years of who-knows-what, of impacts, wind erosion, ices, and even fluids, the region has changed. That we have to look carefully for something as small and fragile as fossilized festoons is not surprising. Their present day abundance is not necessarily indicative of historical conditions.

Posted by: dburt Jun 19 2007, 05:32 AM

Sorry Elk Grove Dan, I didn't make myself clear. I meant: Why don't we see them continuously exposed at the same preserved level of alleged sheet water flow in areas of adequate outcrop, such as in the wall of a little crater? (Payson outcrop, I believe that area was called.) In that regard, why haven't we seen any water channels at all? Flowing water always seems to find a way to erode channels, especially in soft sand or mud, and channels are the most commonly accepted evidence for regional water flow on Mars images (together with teardrop shaped islands, perhaps). The pictures I saw of terrestrial "festoons" presented at a meeting were all in restricted areas of former waist-deep sheet water flow right next to an enormous river channel. That big river struck me as a little odd as an analog for Meridiani. I've personally seen nice "festoons" exposed only in the same environment, preserved in sandbars on the banks of the Colorado River in the Grand Canyon - again, not a possible analog for Meridiani.

For over 30 years I've taught my freshman classes that a sand-choked water flow will generally take the form of a braided stream, with dozens of little channels branching and rejoining as they make their leisurely way across a nearly flat sandy plain. Those branching and rejoining channels are the only evidence for flowing water I've ever seen on flat sandy surfaces where deposition is occurring. An example I studied on June 1 was at top of the dune-deposited Jurassic Page Sandstone, of Page, Arizona, where it was eroded down to the plane of the water table, and then washed by the water flows that deposited the Entrada Sandstone on top of it. No "festoons" at all - just dozens of little branching channels seen almost anywhere in sandstones on top of that planar erosion surface. Hike the Rim Trail that encircles the town of Page and you'll also see beautiful views over Lake Powell, and tons of hematitic concretions that don't look anything at all like the Meridiani spherules, except that they're kind of round. BTW, ephemeral braided streams are almost universal in sandy flat areas of the modern Arizona desert too, unless we're in the midst of a scouring flash flood.

So even if the "festoons" are real and not an unfortunate artifact of viewing angle, 1) something that looks just like them apparently has formed in various surge deposits too and 2) they are a highly atypical indicator of flowing water in a flat sandy environment (sort of like the 3rd dead grandmother in my little parable above). That is, possible but not plausible, and certainly not the best indicator for flowing water (highly ambiguous, as it turns out).

Note: I don't consider myself a sedimentologist. Knauth teaches that course and does that research, and I've learned something from him and from a lifetime of field work.

I hope I'm not getting too technical for most of you. I'm really trying to avoid that. Oh well, vote with your eyes, I guess, but please let me know. smile.gif

--Don

Posted by: ElkGroveDan Jun 19 2007, 06:26 AM

QUOTE (dburt @ Jun 18 2007, 09:32 PM) *
I hope I'm not getting too technical for most of you.

Don't know about anyone else but I'm jogging along right next to you Don. I may be rusty on my physics and calculus, and TD is just a painful memory but I've kept my background in geology and geophysics well-polished.

Posted by: marsbug Jun 19 2007, 02:50 PM

I'm no geologist or chemist but the impact surge argument seems very straight foward and logical, possibly more so than any other hypothesis I've heard. I understand that the chemistry of home plate is very suggestive of the presence of water. Could the chemistry of home plate be accounted for by the impact surge hypothesis alone, or would the occasional presence of water still be required?

Posted by: dvandorn Jun 19 2007, 03:05 PM

My wonderment with the impact surge theory is how it resulted in the finely layered rocks we've been calling evaporite. That would require, through the 800 meters estimated thickness of the unit, tens of thousands (if not more) separate impact surges, would it not? Each one depositing a millimeter-thick layer with only occasional cross-bedding? And the variations in chlorine and bromine -- those are excellently explained by hydrodynamics. How does impact surge theory explain them?

I see tens of thousands of dead grandmothers lurking here...

-the other Doug

Posted by: centsworth_II Jun 19 2007, 03:34 PM

QUOTE (dvandorn @ Jun 19 2007, 11:05 AM) *
...the 800 meters estimated thickness of the unit...

The mind boggles. Opportunity is looking at the tiniest fraction of the
overall history of Meridiani. I don't think the base surge explanation
for the festooned layers that Opportunity has seen denies that the overall
800 meter deep stack of evaporites could have been laid down in the bed
of an ancient sea. The base surge theory only says that an impact would
rearrange that material into the small scale features seen by Opportunity,
in the limited range of layers that she is looking at.

It's the festoons -- the small smiley-faced ones that it's said could be
formed in a matter of hours, or minutes -- that concern me. I think
it's legitimate to ask what caused the water flow that would be
necessary to form them. What rate of flow is necessary?

The way I see it, the berries could very well be concretions formed in water
long after the festoons formed, by whatever means. In this case,
the berries do not need to be explained by the base surge theory.

Posted by: dvandorn Jun 19 2007, 03:52 PM

Oh, believe me, I'm grateful for the Professor in bringing up the impact surge theory. Impacts have shaped the surface of Mars moreso than they have of Earth, and any geological analysis that doesn't take that into account is ignoring a bunch of 800-lb gorillas in the room, so to speak.

As for the lack of braided channels in the layers we can see -- that bothers me, too. Always has. I wonder a bit about the movement of water in a lower-gravity environment, and whether or not this could have an effect on channeling in shallow water. But when I look at various images of Meridiani, I do see evidence of mud-cracking-type features (such as Anatolia).

Taking everything altogether, Occam's Razor points at water, to me. But I seriously appreciate the concept of alteration by impact processes, since such processes *must* have been occurring throughout the formation of these units.

-the other Doug

Posted by: Floyd Jun 19 2007, 04:29 PM

In general I think we are talking about standing water, not flowing streams. Is the atmosphere of Mars strong enough to ripple the surface of a lake such that festoons form on a sandy bottom?

Posted by: centsworth_II Jun 19 2007, 06:55 PM

QUOTE (dvandorn @ Jun 19 2007, 11:52 AM) *
...when I look at various images of Meridiani, I do see evidence of
mud-cracking-type features (such as Anatolia). Taking everything
altogether, Occam's Razor points at water, to me.

This does not have to be either/or: Water or base surge.

Water for the original evaporites. Water for the vugs, concretions,
and "mud cracks". I can see all that. But I'd like to see more on
how the small, smiling festoons were caused by surface water.

Posted by: stevesliva Jun 19 2007, 11:22 PM

QUOTE (dvandorn @ Jun 19 2007, 11:05 AM) *
My wonderment with the impact surge theory is how it resulted in the finely layered rocks we've been calling evaporite.

I wonder if the atmospheric conditions over quite a larger area would gain higher levels of vapor, condensation, precipitation after an impact... given the explanation for frost at the Viking sites involving CO2 precipitation, I won't hazard to guess what materials CO2, H2O, liquid-hot magma, etc are involved. But fine-layering, I'm sure there's some way that's compatible with overlapping clouds of vapor created by various impacts.

Posted by: dburt Jun 19 2007, 11:41 PM

Nice to hear that my remarks of last night have generated some more discussion. I have to sleep, hug my wife, and do my day job too sometime, so sorry I can't chime in more often. Glad also to discover that I haven't been too technical yet, and that all are following the "dead grandmothers" argument without being a professor or teacher (of course, among us it's a standing joke that grandparents seem to die only on test days).

With regard to some of the preceding comments, at Meridiani and Home Plate the amazing rovers are imaging only the same surface rocks that can be imaged from orbit, but in infinitely more detail and from many more angles, along with multiple instruments that yield compositional and mineralogical-petrological information. The brush and RAT, plus unintended wheel dragging, have been exceedingly helpful too. Still, what lies beneath either site can only be guessed at, except where impacts have excavated samples of deeper rocks.

Impact cratering at Victoria Crater has excavated only the same sandy, salty, cross-bedded, spherule-rich rocks seen earlier in Endurance and Eagle craters - no signs whatever of standing water (i.e., no shales or lake beds). Driving into the crater may reveal more (e.g., a detailed record of layering, called stratigraphy by geologists), but it is unlikely to reveal any new rock types. Orbital imaging suggests deeper rocks (nearly a kilometer thick, and therefore potentially much older than those at the surface) are also finely layered, and, most intriguingly, Ken Edgett's 2005 article in the Mars Journal suggests that some of these deeper rocks may contain flow channels of some sort. It would be highly premature to state what geological processes (water, wind, volcanism, impact) might have formed these older, deeper beds without looking at them up close, however. We have never claimed that they are all impact deposits - we have just stated that some or all of them could be, because Edgett also noted that they appear to be interstratified with numerous impact craters, indicating that lots of cratering was going on as they were deposited. Keep in mind that impact deposits can be channeled like any other rock - the channels don't indicate water deposition, only erosion. Also, processes other than water flow can erode channels too, as Nick Hoffman has emphasized in his "White Mars" interpretations of outflow channels and young gullies. There are plenty of gaseous mixtures that, in bulk, have much in common with a watery fluid. (Steamy, high-velocity surge clouds making various types of cross-beds, for example.)

Impact cratering inside (or in the region of) Gusev Crater does not appear to have excavated any of the expected lake beds either - just variably vesicular lavas (some or all of which might instead be impact melt - on the surface we see only the broken pieces, not the lava flows) and possible small pieces of layered surge beds. On the other hand, no particularly deep craters have or will be (given its dragging wheel) visited by Spirit. If there were a small explosive volcano nearby, it could have excavated rocks going all the way down to its source region (region of rock melting - very deep indeed). Unfortunately, no volcanic constructs or explosive craters are visible nearby, despite possible volcanic indicators in the cross-bedded surge rocks of Home Plate, which are more likely simply more impact surge (I've made no secret about that being our present interpretation).

The above stratigraphic review is just to demonstrate that we haven't made any of the possibly outlandish claims about impact deposits that some people seem to have attributed to us. Our working hypotheses are strictly based on the daily images and published data that has been released to date, and mainly concern the youngest rocks (those exposed at the surface and imaged by the rovers).

Posted by: David Jun 19 2007, 11:52 PM

QUOTE (dburt @ Jun 19 2007, 11:41 PM) *
no particularly deep craters have or will be (given its dragging wheel) visited by Spirit


Except for that insignificant little depression called "Gusev"... tongue.gif

Posted by: AlexBlackwell Jun 19 2007, 11:56 PM

QUOTE (dburt @ Jun 19 2007, 01:41 PM) *
Nice to hear that my remarks of last night have generated some more discussion. I have to sleep, hug my wife, and do my day job too sometime, so sorry I can't chime in more often.

You have to learn to put UMSF at the head of the above-listed queue. Of course, then you'd have to add "see a divorce lawyer and go to the unemployment agency" at the end cool.gif

Posted by: dburt Jun 21 2007, 12:46 AM

QUOTE (marsbug @ Jun 19 2007, 07:50 AM) *
I'm no geologist or chemist but the impact surge argument seems very straight foward and logical, possibly more so than any other hypothesis I've heard. I understand that the chemistry of home plate is very suggestive of the presence of water. Could the chemistry of home plate be accounted for by the impact surge hypothesis alone, or would the occasional presence of water still be required?


Superb question! Really sets me off (the flattery doesn't hurt either biggrin.gif ). In principle, what impacts do is vaporize, excavate, and scatter what was already in the target volume, as modified by vapor condensation and generally minor chemical input from the impactor (a comet or meteorite). Turbulent surges also scour the surface across which they flow, possibly modifying the cloud chemistry. Impact doesn't create anything new, except high pressure minerals and impact melt (and vapor and condensates, including spherules) - it's main effect is to homogenize and scatter what was already there.

Most salts at Meridiani (except jarosite which, following Roger Burns, we attribute to iron sulfide weathering - impact acid steam condensation has alternatively been suggested by a colleague, Misha Zolotov) probably formed in liquid water (brine) long before impact may have scattered across Meridiani. If early Mars worked like early Earth, the salts mainly date back to shortly after the planet formed, when acid steam, released by planet-wide degassing, condensed into the first warm seas. The acids rapidly reacted with basic rocks like basalt to form neutral salts containing Mg, Ca, and Na.

To concentrate the dissolved salts into a dense brine or crystals, we like freezing more than evaporation. That is, given the choice between hot vs. cold for early Mars, we choose cold, because Mars has always been much farther from the Sun and much smaller than Earth. As the seas froze down and the ice sublimated, the brines beneath got more and more concentrated (denser), and gradually sank into the subsurface, where they were trapped beneath ice or permafrost.

Whether cold or hot (relatively), early Mars was certainly bashed by impacts, probably most of them just before 3.8 billion years ago (the so-called late heavy bombardment). These impacts obliterated the early surface history of Mars and scattered salts and, we hypothesize, sulfides across the surface. Afterwards, the surface of Mars was about as it is today, extremely cold and dry, with an atmosphere close to a vacuum, so that liquid water (and even ice in most places) was unstable or extremely ephemeral. Large amounts of water apparently survived in the subsurface, however, as both ice and (probably) deep brine (as evidenced by occasional catastrophic releases to outflow channels that possibly formed ephemeral seas in the northern lowlands).

We tentatively date the Meridiani surface rocks (= youngest geologically) to the tail end of the late heavy bombardment period, when the surface of Mars already could not support liquid water as streams or lakes (given that there is no geological evidence of any at Meridiani - in this our interpretation differs completely from that of the MER team). The surface climate matters very little for the impact process itself, but does affect the preservation potential (cold and dry = very slow wind erosion only, allowing weak Meridiani sediments, cemented only by soluble salts, to survive until the next distant impact buried and preserved them). So to answer your question (you say, at last!), no liquid water is indicated by the salts, other than minor quantities resulting from condensation of steam in the original surge cloud, or whatever the salts themselves could attract from the atmosphere (i.e., water in surface brine films and occasional drips). This minor water was enough to rust sulfides and dissolve (leach) the most soluble salt (probably a chloride), leaving hollow crystal cavities, but was not enough to crystallize clays, destroy jarosite, recrystallize the soluble salts in bulk (reducing rock permeability to zero), or form the extremely coarse (giant in places) salt crystals that characterize actual evaporites or other water-soaked salt deposits. Our impact surge hypothesis resembles the extremely complex one of the MER team only in that we agree that the salts must have been transported from somewhere else (a realization they apparently came to only after we had pointed out to them, in our initial "brine splat" presentations of 2004, conceptual problems with having the most soluble and least soluble salts intimately mixed together in an alleged evaporite). That "somewhere else" could be any large salt concentration in the subsurface for us, or a hypothetical giant vanished playa lake (for which there is absolutely no surface or shallow subsurface evidence at or near Meridiani) for them. Our hypothesis can be generalized to any sandy, salty, layered sequence on Mars (including Home Plate in Gusev Crater), theirs cannot. Our allows for the actual appearance and extremely broad distribution of "blueberries" as impact-derived spherules (with similar-appearing ones occurring at Home Plate and probably many other places); theirs does not. And so on and so on, but I hope you are getting the general idea. I emphasize that the above impact story is merely a working hypothesis that undoubtedly is wrong in some details, but in its present form it appears consistent with all available evidence (I trust everyone will feel free to disagree vociferously).

Wow, ask a simple question and get a simplified geological history of Mars! What a deal! Oh well, you know me by now. As Arne said in T2, "Of course, I'm a terminator", I say "Of course, I'm a herr doktor professor" (who kills grandmothers by his tests, and every else by his long lectures...). smile.gif

Posted by: nprev Jun 21 2007, 01:07 AM

biggrin.gif ...you're killing me, Professor; none of my profs ever had a sense of humor like this...

One quick question re the 'ancient salts' hypothesis: What about the atmospheric effects of comparatively recent vulcanism such as the Tharsis Uplift? (IIRC, that's thought to have happened 100-200 MY BPE). It seems reasonable to assume that most of the outgassing was CO2 and water accompanied by a rise in atmospheric pressure (how much & for how long, no idea...though the Big Four are, like, big, so thinking that this had to go on for some time).

Anyhow, what I'm wondering is how apparently water-soluable salts could have survived near the surface during this epoch; certainly atmospheric water vapor should have penetrated the surface below the first few inches of the soil. This makes me think that these deposits were produced later in Martian history after vulcanism subsided and the atmosphere devolved into its present state.

Posted by: AlexBlackwell Jun 21 2007, 01:09 AM

QUOTE (nprev @ Jun 20 2007, 03:07 PM) *
biggrin.gif ...you're killing me, Professor; none of my profs ever had a sense of humor like this...

Yes, laughing at the professor's jokes is one way of improving your grade biggrin.gif

Posted by: nprev Jun 21 2007, 01:23 AM

Oh, yeah...but I don't have to force it here! tongue.gif

Posted by: centsworth_II Jun 21 2007, 01:41 AM

QUOTE (dburt @ Jun 20 2007, 08:46 PM) *
Our hypothesis can be generalized to any sandy, salty, layered sequence on Mars...
theirs cannot. Our [hypothesis] allows for the actual appearance and extremely broad
distribution of "blueberries" as impact-derived spherules...theirs does not. And so on...

So when is some geological society going to host a conference where proponents
of these theories can face off. It would be good to get more geologists with varied
expertise and experience weighing in.

Posted by: Bill Harris Jun 21 2007, 01:55 AM

QUOTE
...no liquid water is indicated by the salts, other than minor quantities resulting from condensation of steam in the original surge cloud, or whatever the salts themselves could attract from the atmosphere (i.e., water in surface brine films and occasional drips). This minor water was enough to rust sulfides and dissolve (leach) the most soluble salt (probably a chloride), leaving hollow crystal cavities, but was not enough to crystallize clays, destroy jarosite, recrystallize the soluble salts in bulk (reducing rock permeability to zero), or form the extremely coarse (giant in places) salt crystals that characterize actual evaporites or other water-soaked salt deposits.


You are wrong.

--Bill

Posted by: centsworth_II Jun 21 2007, 02:09 AM

QUOTE (dburt @ Jun 20 2007, 08:46 PM) *
...no liquid water is indicated by the salts, other than minor quantities...

And besides the large amounts of liquid water involved in the original
formation of the salts, right?
QUOTE (dburt @ Jun 20 2007, 08:46 PM) *
If early Mars worked like early Earth, the salts mainly date back to shortly
after the planet formed, when acid steam, released by planet-wide degassing,
condensed into the first warm seas. The acids rapidly reacted with basic rocks
like basalt to form neutral salts containing Mg, Ca, and Na.

Posted by: dburt Jun 21 2007, 02:52 AM

QUOTE (centsworth_II @ Jun 19 2007, 11:55 AM) *
This does not have to be either/or: Water or base surge.

Water for the original evaporites. Water for the vugs, concretions,
and "mud cracks". I can see all that. But I'd like to see more on
how the small, smiling festoons were caused by surface water.


A "mud crack" is formed in mud, by definition. No layer of mud (called shale when hardened into a rock) has yet been imaged anywhere at Meridiani, so far as I know. Therefore, no mud cracks. (This term has not, so far as I'm aware, been used by the MER team.) The polygonal cracks that affect the layered rocks have been called "bulk shrinkage cracks" and can occur in various types of rocks - what environment they indicate is therefore ambiguous. They could indicate drying (shrinking) of clays (as in mud), dehydration of salts, a response to temperature decrease (like columnar jointing in lavas - vertically oriented bulk shrinkage cracks whose orientation is controlled by the flat geometry of the flow as it cools and shrinks), or some other process.

FWIW, polygonal bulk shrinkage cracks are common in sandy, cross-bedded surge deposits (which of course is what we believe Meridiani consists of). Such shrinkage presumably occurs as the rocks cool and they lose the steam that permeated the them during deposition. See Knauth's 4th figure here:

http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1869.pdf

We were together when he took that photo; I've seen similar shrinkage cracks in other surge deposits.

As per salts implying water, see my above "terminator" post (not if the salts were formed earlier and then transported to Meridiani, which is one interpretation we agree with the MER team on).

As per the alleged "festoons", see my post of a day or two ago - "festoons" need not indicate flowing water, because they apparently can form in surge deposits too (a different type of flow), and most at Meridiani may simply be an artifact of viewing angle (which I'm still hoping someone here can confirm or prove wrong). "Festoons" are a cross section through "current ripple marks" (tiny moving sand dunes, conceptually) and form in a manner distinct from "oscillation ripple marks" which form in very shallow water due to the influence of surface waves on the water.

Only minor water, such as liquid condensed from the steamy surge cloud or water attracted from the air by the salts itself, is needed to leave the Meridiani crystal cavities (again, see my "terminator" post). (BTW, the technical adjective for salts that attract water - most do - is hygroscopic or, in extreme cases such that a salt attracts so much water that it liquifies in place - self dissolves, as it were - is deliquescencent.) Calcium chloride, probably a common salt inside Mars, is deliquescent, and it is commonly used in laboratories as a drying agent because it sucks so much moisture out of the air.

And of course, the only water needed to form what the MER team calls "concretions" is condensing steam (or another vapor) in a surge cloud, if they are impact-related spherules (as their perfectly spherical shape, uniformly tiny size, Ni-enrichment, blue-gray color, and pattern of distribution suggests).

Please prove me wrong. mad.gif

--Don

Posted by: dburt Jun 21 2007, 02:54 AM

QUOTE (centsworth_II @ Jun 20 2007, 07:09 PM) *
And besides the large amounts of liquid water involved in the original
formation of the salts, right?


You got it. Lots of water somewhere, somewhen, but not at Meridiani then (or since).

--Don

Posted by: centsworth_II Jun 21 2007, 03:28 AM

QUOTE (dburt @ Jun 20 2007, 10:54 PM) *
Lots of water somewhere, somewhen, but not at Meridiani then (or since).


Why assume that the salts did not form at Meridiani billions of years ago.
Is it only because they had to form somewhere else in order to be moved
to Meridiani by base surge?

Posted by: dburt Jun 21 2007, 04:25 AM

QUOTE (nprev @ Jun 20 2007, 06:07 PM) *
biggrin.gif ...you're killing me, Professor; none of my profs ever had a sense of humor like this...

One quick question re the 'ancient salts' hypothesis: What about the atmospheric effects of comparatively recent vulcanism such as the Tharsis Uplift? (IIRC, that's thought to have happened 100-200 MY BPE). It seems reasonable to assume that most of the outgassing was CO2 and water accompanied by a rise in atmospheric pressure (how much & for how long, no idea...though the Big Four are, like, big, so thinking that this had to go on for some time).

Anyhow, what I'm wondering is how apparently water-soluable salts could have survived near the surface during this epoch; certainly atmospheric water vapor should have penetrated the surface below the first few inches of the soil. This makes me think that these deposits were produced later in Martian history after vulcanism subsided and the atmosphere devolved into its present state.


Owing to plate tectonics, Earth probably has at least as much volcanism today as Mars ever did, plus coal-burning power plants and smelters are continously tossing a sulfuric acid precusor (SO2) into the air. This has minor effects (such as slight climate cooling - which we badly need in Phoenix) but the ground hardly is littered with jarosite, gypsum or other relatively insoluble sulfates. Consider early degassing of an entire molten planet, compared with the little bit of steam and CO2 and SO2 that comes out of a lava flow or even volcanic steam explosion - a drop in the bucket, literally. As I understand it (not my field), the atmospheric pressure on Mars is close to "buffered" by CO2 ice at the poles and in fact Mars has been continuously losing atmosphere very slowly since the end of the late heavy bombardment. Evidence for climate change is mainly blamed on obliquity and orbital variations (how much Mars tilts on its axis and how non-circular its orbit is). Some people try very hard to make Mars temporarily warm and wet with volcanism, which may be possible, given how little atmosphere there is to begin with, but I imagine that this effect could be dwarfed ty the effect of a large impact (especially during the boom boom boom of the late heavy bombardment). Impact was adequate both to warm Mars up (very temporarily) and deposit thick layers of salty sediments. As should be obvious from my abbreviated history, I'm with the very wet, but very cold and salty school of early Martian geology (at least until more information becomes available). Show me the palm trees, I say, before I bring my swimming suit.

The fact that water soluble salts have survived near the surface is just what makes me think that it hasn't rained on those parts of Mars in 3.8 billion years - or at least, not much. (Snow or frost is okay for survival of sulfates - see below.) In Arizona, after a small rainstorm (something else we badly need), the sulfates on mine dumps sink into the ground owing to dissolution and then, over the next several weeks, they reappear as colorful crusts referred to efflorescences (because they can look like flowers blooming). I think that's what we're seeing in the cauliflower-like crusts of salts being imaged just below the surface at and near Home Plate. The low pressure makes the salts effloresce just beneath, rather than above, the surface. The driving force is simple capillarity and evaporation of moisture - dip a paper towel into salty water, the water rises up (wicks up) by capillarity, and then evaporates, leaving salts behind - far above the surface of the water. And many salts generate their own brine from atmospheric moisture, so that capillarity can make deep salts wick upwards towards the surface, without rain. This effect was much discussed with regard to formation of "sulfate duricrust" during Viking days, but seems to have been largely neglected in recent discussions.

My general attitude (Occam's razor) is I don't want to invoke any unusual effect or phenomenon, especially anything I can't see direct evidence of, until I am forced to by the data. That's how I feel about "warm, wet" early Mars - it seems to me that impact alone, for which there's abundant evidence at every scale, may suffice for a lot of what people want to blame volcanism, or greenhouse gases, or whatever on. Occam was apparently a medieval theologian (and logician) who got upset when people wanted to blame every event or phenomenon on mysterious, invisible angels. I feel the same way about invisible geological features (missing playas and missing volcanoes) on Mars.

BTW, if you want surface water under present martian surface conditions, just dissolve lots of salts in it (mainly chlorides, not sulfates - the sulfates litter the surface, and the chlorides don't, because the sulfates have very little abilty to depress the freezing point of ice). If frost lands on mixed salts, the chlorides are leached, and the sulfates are not. Knauth and I published papers on that in 2002 and 2003, as mentioned in a previous post, I think, and blamed the crystal cavities at Meridiani on the same phenomenon in our 2005 Nature paper.

Playing the professor again, I'm afraid. All out of jokes, though. huh.gif

--Don

Posted by: dburt Jun 21 2007, 04:29 AM

QUOTE (centsworth_II @ Jun 20 2007, 06:41 PM) *
So when is some geological society going to host a conference where proponents
of these theories can face off. It would be good to get more geologists with varied
expertise and experience weighing in.


Ever hear of the "lunatic fringe"? That's us, in most people's eyes. tongue.gif

Posted by: dburt Jun 21 2007, 04:32 AM

QUOTE (Bill Harris @ Jun 20 2007, 06:55 PM) *
You are wrong.

--Bill


Quite probably, but how? (Despite being a professor, I am teachable, I hope.)

Posted by: dvandorn Jun 21 2007, 04:50 AM

QUOTE (dburt @ Jun 20 2007, 11:25 PM) *
...missing volcanoes ...on Mars.

Ummm... if the Tharsis shield volcanoes and dozens of other classic calderas readily observed on Mars aren't volcanoes, and if the very clear and obvious lava flows (which read as basalt from both surface and orbital spectral analysis) aren't volcanic, then what are they?

I hate to say this, but if your theories are based even a little tiny bit on this "observation" that Mars is "missing volcanoes," then you do seem to be ignoring empirical data (labeling it "theoretical") that doesn't fit with your own theories, and that's when the scientific method fails.

I'm sorry -- I simply *must* have misinterpreted what you mean, here, since that statement is so obviously false.

-the other Doug

Posted by: dburt Jun 21 2007, 05:41 AM

QUOTE (centsworth_II @ Jun 20 2007, 08:28 PM) *
Why assume that the salts did not form at Meridiani billions of years ago.
Is it only because they had to form somewhere else in order to be moved
to Meridiani by base surge?


Good question. If I understand it, your argument is they had to form somewhere, so why not at Meridiani, where we find them? (Great example of Occam's razor at work, by the way.) I don't want to write another long post, because I'm about to go home, but maybe I can practice with a short one. The basic arguments are several: 1) We see no evidence of a geological environment that would permit salts to grow at the surface - no shales, meaning no standing water for an evaporite basin or even puddle - not even in deep material excavated from Victoria. The playa lake, if any, has "vanished". 2) The Meridiani salts appear to be an intimate mixture of highly soluble and highly insoluble salts (a mechanical mixture, in other words) plus poorly characterized fine debris (not crystalline clays). Salts crystallize out of an evaporite basin in inverse order of solubility - least soluble first, in a "bathtub ring" around the outside fringe (usually gypsum), and then more and more soluble salts in zones towards the center. Meridiani is nothing like this. The MER team agrees with us that the salts had to come from somewhere else - they invoke wind transport and mixing (reasonable - plenty of wind on Mars), we invoke impact transport and mixing (plenty of evidence of impacts, of all ages, but especially for early Mars). 3) The salts are very fine grained and the rocks appear uniformly porous and permeable. Growth from water, or soaking in water, would have caused permeability decrease and crystal size increase. This argues strongly against the MER team interpretation that the salty rocks were soaked in brine many times after they were deposited, and that brine mixing in a huge, uniformly permeable volume produced concretions. (The US Government permanently stores military radwaste in evaporitic salt beds, because they are so impermeable.) There are other more subtle geochemical arguments, but those 3 are the easiest to understand, I think. Let me know if you need clarification.

Well, out to play in the real desert (i.e., go home) cool.gif . Soon the daily summer afternoon dust storms (haboobs) will begin in Phoenix (sort of a very dilute, relatively slow-moving, cool, dry analog for a ground-hugging surge cloud - but something that a martian surge cloud could easily decay into with distance, perhaps). Thank y'all very for your comments (even you, Bill Harris - I really admire your succinctness biggrin.gif ).

--Don

Posted by: centsworth_II Jun 21 2007, 03:10 PM

QUOTE (dburt @ Jun 21 2007, 01:41 AM) *
Let me know if you need clarification.

Ok, everyone agrees that the sulfates were moved to their present location from
elsewhere. I'm wondering about the very fine layering seen at Meridiani. I have
a hard time imagining such fine layers being formed by such a violent, sudden
activity like base surge. Do you have any feeling for what depth of layering
would be attributable to a single base surge event?

Apart from the fine scale festoons that the MER team attributes to water, there
are the massive chunks that really do look like fossil dunes (or large wind ripples).
Do you also attribute those to base surge?

Even assuming that the layers and berries could be the result of base surge, I
have a hard time understanding the formation of the large crystals whose
dissolution formed the vugs. You've said:

"No more moisture is required than would be present in the original surge cloud
(mainly condensing steam) or could later be removed from the atmosphere by
water-attracting (hygroscopic or deliquescent) salts."


And:

"Only minor water, such as liquid condensed from the steamy surge cloud or water
attracted from the air by the salts itself, is needed to leave the Meridiani crystal cavities"


Is the formation of such large in-ground crystals by trace water (on Earth) a geological
observed fact? Or is it a "fringe" hypothesis? I have no real geological background.

Posted by: dvandorn Jun 21 2007, 03:59 PM

Yes -- I brought up the finely layered nature of the rocks at Meridiani before, and that question was never addressed by the Professor. I can see these rocks being built up by aeolian deposition of millimeter-deep layers over the course of tens of thousands of years, laid down on wet ground (and possibly onto shallow standing water), far more than I can see tens of thousands of base surges, each laying down a very thin, very flat layer of rock of consistent composition to the last base surge, each laying down a very flat, very thin layer with almost no turbulence developing along the surge/ground contact.

Such surges would, I would think, have enough energy in them that we would see scouring and channeling -- the very same types of landforms whose lack that the Professor cites as a disproof of standing water or a playa environment. If these layers were laid down by an energetic base surge, how can they be so overwhelmingly flat, with very little sign of any turbulence? (Remember, the cross-bedding we've seen is the exception, not the rule, in these rocks.) Are you postulating that there were *no* surface features that would have caused turbulence in the surge/ground contact? (We may not be able to watch and observe a surge in detail, but we have a ton of similar surge-emplaced landforms that we have observed in great detail on the Moon, and even with a lack of atmosphere, we see evidence of a fantastic amount of turbulence in the debris flows that generated terrain on Luna.)

I also have a difficult time understanding how these deposits could have been laid down at the end of the Late Heavy Bombardment. There is visual evidence supporting the theory that the rough, cratered terrain generated by the LHB actually underlies the Meridiani deposits. You'd have to assume, based on the range of crater-like landforms, the relative lack of large craters, and the relative flatness of the terrain, that the nearly kilometer of Meridiani deposits were laid *after* the LHB had finished. In other words, if the Meridiani unit was generated by tens of thousands of impacts at the end of the LHB, why would the unit not have been broken up by these impacts as quickly as the base surges laid it down? What makes Meridiani so special that it could be laid down by impacts all around it but not suffer any impacts in the area itself, thus leaving this layered unit (which would have required millions of years of base surges to lay down) mostly intact?

Occam's razor suggests that we're seeing an entire population of dead grandmothers here... smile.gif

-the other Doug

Posted by: dburt Jun 21 2007, 10:51 PM

QUOTE (dvandorn @ Jun 20 2007, 09:50 PM) *
Ummm... if the Tharsis shield volcanoes and dozens of other classic calderas readily observed on Mars aren't volcanoes, and if the very clear and obvious lava flows (which read as basalt from both surface and orbital spectral analysis) aren't volcanic, then what are they?

I hate to say this, but if your theories are based even a little tiny bit on this "observation" that Mars is "missing volcanoes," then you do seem to be ignoring empirical data (labeling it "theoretical") that doesn't fit with your own theories, and that's when the scientific method fails.

I'm sorry -- I simply *must* have misinterpreted what you mean, here, since that statement is so obviously false.

-the other Doug


You got me. Sorry, I guess I should have explained myself much better. I didn't mean the giant Tharsis and similar basaltic volcanoes, which are nowhere near Meridiani, and are non-explosive (Hawaiian style flowing lava only, in general). I meant the small "invisible" exploding volcano presumed by the MER team to have produced the surge deposits at and near Home Plate (that type of steam explosion generally leaves a highly visible crater or construct - consider Diamond Head in Honolulu, which is of this type - and the deposits are usually very local, extending only few kilometers). I also meant the likewise "invisible" but necessarily very much larger Yellowstone Park-style "supervolcano", that McCollom and Hynek (2005, in the same Nature issue as our impact paper) hypothesized for producing Meridiani. Perhaps they saw the recent Discovery Channel film "Supervolcano." It has an excellent depiction of a giant volcanic surge cloud from Yellowstone killing several geologists fleeing in a truck, wheras their boss, in a helicopter high overhead, survives because the flow was hugging the ground. A similar volcanic surge cloud is depicted towards the end of the film "Dante's Peak". No such giant exploding supervolcanoes have yet been documented on Mars, to my knowledge, although various people have called upon them to produce layered deposits. Impacts, for which there is abundant evidence, seem more logical to me.

You mean you can't read my mind? laugh.gif

--Don

Posted by: dvandorn Jun 22 2007, 12:00 AM

That makes sense, Don -- though IIRC, isn't there a large, heavily eroded caldera structure in the middle of Meridiani Terra, which (in global terms) lies adjacent to Meridiani Planum? Could be a source of volcaniclastic materials in the Meridiani Planum area, could it not?

I'm still interested in how you explain the finely layered nature of the rocks seen at Oppy's landing site (and, by inference, the entire 800m thick Meridiani unit). And I'd love to see computer simulations of the turbulence at the surge/ground contact... smile.gif

-the other Doug

Posted by: dburt Jun 22 2007, 12:28 AM

QUOTE (centsworth_II @ Jun 21 2007, 08:10 AM) *
I'm wondering about the very fine layering seen at Meridiani. I have
a hard time imagining such fine layers being formed by such a violent, sudden
activity like base surge. Do you have any feeling for what depth of layering
would be attributable to a single base surge event?

Apart from the fine scale festoons that the MER team attributes to water, there
are the massive chunks that really do look like fossil dunes (or large wind ripples).
Do you also attribute those to base surge?

Even assuming that the layers and berries could be the result of base surge, I
have a hard time understanding the formation of the large crystals whose
dissolution formed the vugs. You've said:

"No more moisture is required than would be present in the original surge cloud
(mainly condensing steam) or could later be removed from the atmosphere by
water-attracting (hygroscopic or deliquescent) salts."


And:

"Only minor water, such as liquid condensed from the steamy surge cloud or water
attracted from the air by the salts itself, is needed to leave the Meridiani crystal cavities"


Is the formation of such large in-ground crystals by trace water (on Earth) a geological
observed fact? Or is it a "fringe" hypothesis? I have no real geological background.


Excellent questions. I'll start with the fine layering. That fine layering and cross-bedding was what most astonished me the first time I was exposed to volcanic surge deposits in Utah, while studying volcanic rocks as possible sources for uranium (under a government-university contract) in the late 1970's. The deposits had been misidentified as "water laid tuff" for about 15 years by a few Geological Survey employees, who couldn't believe it either (they ignored the lava flows on top, which might have suggested volcanism). Of course, they were mineral deposit types and sedimentologists who had never studied volcanoes before, whereas I cheated by having a leading expert on explosive volcanism (former ASU Prof. Mike Sheridan) with me at the time, which unfairly helped the diagnosis. Co-author, Ken Wohletz, a doctoral student at the time, was along and did his ASU Ph.D. thesis on surge deposits, before he was hired at Los Alamos. (BTW, a 1983 paper by Wohletz and Sheridan first suggested that Mars rampart crater ejecta should be examples of impact surge deposits.)

While I'm recounting history, in the mid-1950's Gene Shoemaker (who later became world famous for his studies of impact cratering) started out studying volcanic surge surge deposits in New Mexico and Arizona (looking for uranium too) before returning to school to complete a Ph.D. dissertation on Meteor Crater, AZ. He couldn't believe the giant sandy cross beds (dune forms) he saw were caused by explosive volcanism either, and initially attributed them to wind action. (Even most volcanologists were making similar mistakes in that era.) Since then studies by numerous volcanologists (clued in by nuclear bomb tests, where surges and their cross-bedded deposits were first described) have documented that thin bedding, low-angle cross-bedding, high angle cross-bedding, dune forms, and ripple forms can occur in surge deposits, all features that excellently mimic wind or water deposition. Both air and water are fluids that carry solids. Evidently, a hot, turbulent suspension of divided solids in a rapidly-moving gas cloud behaves as a fluid too. The stickiness that condensing steam gives to particles apparently can help them be deposited more rapidly than normal sediments (truly wet surge deposits can be plastered onto the side of trees). Some terrestrial surge deposits appear so ambiguous that non-volcanologists are still arguing with volcanologists over volcanic vs. wind-caused deposition - and those are the deposits that occur next to a crater (information from Wohletz).

The extremely poor sorting (mixture of large and small pieces), together with the cross-bedding and fine layering, is fairly diagnostic of surge deposits close to the explosion site, but sorting increases with distance, so that a mainly sandy deposit can be hard to diagnose. Bomb sags, caused by ballistic ejecta of rocks by the explosion, have been used to diagnose volcanic surges (e.g., at Home Plate), but ballistic ejecta are also typical of impacts. Disseminated accretionary lapilli resembling the Meridiani "blueberries" (except in composition) are common in some volcanic surge deposits, and would never be expected in a wind- or water-deposited sediment. (Post depositional concretions tend to be much more irregularly sized, shaped, and distributed than accretionary lapilli.)

The thickness of the deposits depends on the size (magnitude) and distance of the explosion - but several meters to several tens of meters are typical of volcanic deposits, where the explosions involved much less energy release than a decent-sized impact releases. For very small volcanic surge deposits (such as those protected from erosion by overlying basalt flows at Peridot Mesa, AZ) you can hike out and follow the gradual transition from several 10's of meters of coarse, cross-bedded ejecta (containing blocks 1 m or more across) to a thin deposit only a few cm thick, consisting of well-sorted fine sand - still finely layered, with shrinkage cracks resembling those at Meridiani.

As for large, in-ground crystals: I invite you to go to an Arizona rock shop and buy a "desert rose". These are fairly large crystals (up to many cm across) that form in damp desert soil from the little moisture available. They are made of gypsum, hydrated calcium sulfate, a salt mineral reported from Meridiani (the least soluble one). Or take some wall-board, which is made of fine gypsum, moisten it in a jar for a few weeks, and watch it "rot" as it recrystallizes (as wall-board in a home will do if made damp for too long). I haven't carried out this experiment: let me know the results if you try it.

We hypothesized that the Meridiani crystal cavities were caused by some type chloride salt crystals that grew right after surge deposition, when things were still warm and very damp - early diagenesis, a sedimentologist might call it. Leaching could have occurred later, by frost.

That's all for now - got to go to a meeting. Hope this answers your questions.

--Don

Posted by: Shaka Jun 23 2007, 01:12 AM

QUOTE (dburt @ Jun 21 2007, 02:28 PM) *
Excellent questions. I'll start with the fine layering.

---snip---
That's all for now - got to go to a meeting. Hope this answers your questions.

--Don

Prof Don,
First let me thank you for the time you have taken to explain your hypothesis and clarify questions from our members. Let me also compliment you on the lucid arguments you have prepared. I find it hard to imagine that many of your students would need to participate in the exam-week "Slaughter of the Innocents", given the clarity of your explanations.

That said, I must suggest that your answer above has tended to skirt the issue of the laminated structure of the Burns Formation as it relates to impacts. Your interesting anecdotes do an excellent job of showing how explosive volcanism on Earth could produce laminated, even cross-bedded, sediments of a similar appearance, and I, for one, would agree entirely with such an alternate cause if there were a range of stratovolcanos evident on the margins of the Meridiani Planitia. A series of wind-blown ash clouds from cyclic eruptions or periodic pyroclastic flows might produce something like a Burns Formation, given a long enough volcanic history, but, as you indicate, this kind of vulcanism is not prominent on Mars. Of course, the accumulated ash would grow enormously thicker and more pronounced than the Burns layers as one approached the source volcanos. I think the MOC imagery would have revealed some trace of this by now.

But that is quite apart from the question as to whether bolide impacts could produce an accumulation of ejecta resembling the Burns Formation. Many of us have a real problem with that. Impacts do form layered ejecta, but generally not more than two or three layers per impact, and these layers are usually quite distinctive lithologically. I think there are about three detectable in the mid North American continent from the Chicxulub impact. The lowermost from the high velocity jets of ballistic ejecta, the middle from the fallback surge of the collapsing ejecta column, and the third from the slow rain of fine distal fallout re-entering the atmosphere globally.

We can see scores to hundreds of layers in the lower parts of the Victoria capes. They are remarkably uniform in scale and appearance. Since a rain of meteorites would distribute more or less randomly over Mars, it is hard to credit that some would not land closer to Meridiani and produce much thicker (meter-scale) layers, as can be seen in the Caribbean environs of Chicxulub. It is hard to imagine that the coarser proximal ejecta would not appear anywhere in the series, excepting the Victoria ejecta at the surface.

In many ways this argument is analogous to that which you make for blueberries. How can there be so many, so uniform and limited in size range? Actually I have less trouble believing that a broad, uniform plain of well-mixed thin sand layers, as Meridiani may once have been, could, when exposed to brief episodes of uniform wetting with very limited supplies of slow-moving groundwater, produce a crop of very uniform concretions with very limited growth, before the Big Freeze-Dry stopped everything but the wind.

Furthermore, the berry distribution through the evaporite is even, as might be expected from a growth process strictly confined by a limited supply of solute, rather than random or aggregated as might be expected for accretionary lapilli being tossed and hurled by the violent currents of an impact surge.

I am sure that the MER team model for Meridiani leaves some questions unanswered, but I still think it leaves fewer than the impact or volcanic alternatives. I don't have the chemistry expertise to deal with those issues, but as I drive around the Meridiani Planitia, courtesy of my good friend Opportunity, I get the sense that this has been one of the quieter, more-peaceful corners of Mars for much of its history. It's been a nice place to sit and ponder. smile.gif
Cheers,
Shaka

Posted by: dburt Jun 23 2007, 05:43 AM

QUOTE (dvandorn @ Jun 21 2007, 08:59 AM) *
I can see these rocks being built up by aeolian deposition of millimeter-deep layers over the course of tens of thousands of years, laid down on wet ground (and possibly onto shallow standing water), far more than I can see tens of thousands of base surges, each laying down a very thin, very flat layer of rock of consistent composition to the last base surge, each laying down a very flat, very thin layer with almost no turbulence developing along the surge/ground contact.

Such surges would, I would think, have enough energy in them that we would see scouring and channeling -- the very same types of landforms whose lack that the Professor cites as a disproof of standing water or a playa environment. If these layers were laid down by an energetic base surge, how can they be so overwhelmingly flat, with very little sign of any turbulence? (Remember, the cross-bedding we've seen is the exception, not the rule, in these rocks.) Are you postulating that there were *no* surface features that would have caused turbulence in the surge/ground contact? (We may not be able to watch and observe a surge in detail, but we have a ton of similar surge-emplaced landforms that we have observed in great detail on the Moon, and even with a lack of atmosphere, we see evidence of a fantastic amount of turbulence in the debris flows that generated terrain on Luna.)

I also have a difficult time understanding how these deposits could have been laid down at the end of the Late Heavy Bombardment. There is visual evidence supporting the theory that the rough, cratered terrain generated by the LHB actually underlies the Meridiani deposits. You'd have to assume, based on the range of crater-like landforms, the relative lack of large craters, and the relative flatness of the terrain, that the nearly kilometer of Meridiani deposits were laid *after* the LHB had finished. In other words, if the Meridiani unit was generated by tens of thousands of impacts at the end of the LHB, why would the unit not have been broken up by these impacts as quickly as the base surges laid it down? What makes Meridiani so special that it could be laid down by impacts all around it but not suffer any impacts in the area itself, thus leaving this layered unit (which would have required millions of years of base surges to lay down) mostly intact?

Occam's razor suggests that we're seeing an entire population of dead grandmothers here... smile.gif

-the other Doug


You raise a lot of excellent points, other Doug, which clearly indicate careful thought. I'll try to take them in order. The fine layering I already addressed in a previous post - it is highly typical of surges and for me was their most surprising feature. Deposits laid down solely on wet ground owing to stickiness probably would not be cross-bedded (as every layer seen to date in Meridiani is). Sedimentts deposited in standing (as opposed to flowing) water would never be cross-bedded and would be likely to be fine mud instead of sand unless they were deposited right at the shore or during a sandstorm. The lack of mud beds (shales) and universality of cross-bedding provide our main basis for stating that Meridiani sediments contain no record of standing water (i.e., no playa is possible, at least not to the depth of exposure/excavation in Victoria or the other craters visited by Oppy).

To make cross-bedding, you need erosion (scouring) followed by deposition. For the wind, this is how sand dunes migrate - they are eroded on one side and the sand is then redeposited on the other side, giving you the giant, high-angle cross beds typical of old dune fields. Dunes (and, for wet and sticky enough particles, antidunes, where the dune grows upwind) are also common in surges. Flowing water making current ripples (so-called "festoons") works the same way, but on a smaller scale. Similar-appearing features can also form in surges, apparently, although they appear to be comparatively rare. Most cross bedding in surge deposits is at very low angles, because the particles are generally moving very fast ("whoosh!"). Low angle cross bedding dominates the Meridiani sediments, consistent with surge deposition, but probably not wind.

As for scouring, inasmuch as every cross bed is a record of scouring, I presume you really meant just to ask about channels. Local channels are highly typical of many areas of surge deposition. They usually are attributed to a swirling vortex (part of the turbulence) moving radially outward from the explosion. Linear, radial channels in volcanic surge deposits (such as those resulting from the 1980 eruption of Mt. St. Helens, WA) have been documented by, e.g, Grant Heiken and Sue Kieffer. By our hypothesis of impact surge deposition, the linear grooves visibly radiating outwards from a great many Mars impact craters (as imaged by both MOC and Themis) would be evidence of just such vortices in an impact surge cloud. Burns Cliff itself appears to contain an example of such a scour - it occurs just beneath what the MER team called the "Wellington Contact" and is near the center of, e.g., this raw image from Sol 287:

http://marsrovers.jpl.nasa.gov/gallery/all/1/p/287/1P153661186EFF37MIP2270L5M1.JPG

Unfortunately Oppy was unable to examine this scour up close, but I saw similar appearing scours while examining various surge deposits in Oregon last summer (described by Grant Heiken and visited by Apollo astronauts, in case some lunar craters turned out to be volcanic). The MER team interpretation is that the "Wellington Contact" is a former water table of regional extent (although it has only been imaged only in Burns Cliff), and the dune-deposited sand was wind-eroded down to this planar water table. How the wind could erode such a localized channel BELOW the water table was never addressed, to my knowledge. (The eroded channel is unlikely to be a stream channel, because it contains no coarse material at the bottom, plus it would be conceptually difficult for water OR wind to erode a stream channel below the water table.) Since they made this suggestion, I have examined several former water tables in exposures of the Navajo and Page Sandstones of Arizona, and I have never seen such a channel feature - the contacts are planar, commonly with shale along them where there was local standing water. That's also where lots of hematitic concretions tend to occur, all clumped together in planar masses. Our impact interpretation would be that the "Wellington Contact" is just a large cross-bed, perhaps marking the contact between two successive surge clouds, with the localized scour marking a turbulent vortex in the younger surge cloud. If so, finding such channels on opposite sides of a given crater exposure might indicate a direction radially towards or away from the parent impact crater (something to look for if Oppy successfully enters Victoria).

Your age question I would answer somewhat speculatively by saying that there has been considerable wind erosion of fines in the past 3.8 billion years. Surge clouds usually are energetic enough to ride up over highlands and settle in lowlands (as notably happened in mountainous areas near Mt. St. Helens in 1980, as today evidenced by the pattern of downed trees). The deposits in highlands tend to be thin and to consist mainly of fines, whereas the lowlands deposits are thick and coarse (more resistant to erosion). In other words, the fluid-like surge clouds tend to "pond" in relatively low areas, despite their energy and high velocity, because they are density currents. The Meridiani lowlands were, in addition, selectively protected from later erosion by their "desert pavement" of dense, unusually large (1-5 mm) hematitic impact-related spherules, which may have been lacking or abraded away in the nearby highlands (pure speculation). BTW, areas of layered deposits in the nearby cratered highlands are reported by Edgett (2005), in his thoroughly-documented article in the first issue of the on-line Mars Journal. As mentioned in a previous post, Edgett also documents that cratering was concurrent with deposition of the main Meridiani sequence (and that some of the lower layers appear to be channeled). With regard to flatness - the wind has done a pretty good job of keeping the terrain flat by erosion (clearly visible at Victoria - look at what happened to the coarse fragments of ejecta); Edgett earlier predicted this from orbital imaging. Also, as mentioned above w.r.t. erosion, although surge clouds can override obstacles (unlike liquids like water or lava), they also tend to fill in lowlands ("pond") and, along with later wind erosion/deposition, could have covered up older or coeval craters.

With regard to comparisons with the Moon: The extremely important difference between Mars and the Moon is that Mars had an atmosphere and lots of suburface brine or ice at the time of late heavy bombardment (and still does today, to a lesser amount). In the dry vacuum of the Moon, impact implies predominantly ballistic processes (like fragments shot from a cannon) no matter how small the particle. The only vapor formed was vaporized impactor and vaporized silicate rock, and these vapors apparently condensed almost instantly into tiny glass spherules. It has been suggested that particle-to particle interactions in a vacuum could have produced a gas-like surge cloud on the Moon, but, to my knowledge, no such finely layered deposit was ever spotted by the Apollo astronauts (who were specifically trained to look for them). Constant "gardening" by micro impacts may have degraded any exposures, however (whereas Mars has enough of an atmosphere to largely protect it from most such "impact gardening" - at the outcrop scale, at least.) On Mars the impact vapors must have contained lots of steam (and vaporized salts), allowing turbulent surge clouds to form that in many ways resembled those formed by smaller explosive volcanic eruptions, where the dominant gas involved is also steam. As each turbulent, scouring, particle-rich surge cloud flowed radially outwards along the ground, it mixed with the atmosphere and decompressed and cooled. Steam (and probably vaporized salts) then condensed onto particle surfaces, making them sticky, and causing them to stick together and agglomerate or acrete into spherules called "accretionary lapilli" (a possible origin for the Meridiani "blueberries" - like a tiny rolled snowball made of sticky particulate rock). In this regard, the so-called rampart craters appear to be unique to Mars, and have always been attributed to either the subsurface volatiles ice or brine or the atmosphere (people still argue - Mars scientists will argue about anything smile.gif ).

That's rather a long post, but then you asked rather a lot of questions (all great ones, BTW). I agree with you that there are far too many "dead grandmothers" (a.k.a. implausibilities) still associated with the various Meridiani hypotheses (not unusual for Mars). We arrived at the impact hypothesis by the process of elimination - impact seemed to offer fewer implausibilities than either wind/water or volcanism. For example, if Mars wind today can only erode a few meters per billion years, how could it have deposited nearly a kilometer of sediments at Meridiani? And if all those sediments are sulfate-rich, you might have to evaporate a playa lake deeper than Olympus Mons is tall (sulfates aren't all that soluble). I'll stick with the impact hypothesis for now - impact seems like the only process able to do all the work required (until a better idea comes along). Also, as mentioned in an earlier post, we cannot exclude water, wind, or volcanism in any combination as having contributed to the unstudied deeper layers at Meridiani or anywhere else, although we suggest that they might not much be needed.

Impact surge isn't the only plausible depositional process associated with impacts (ignoring the obvious ballistic ejecta, think about all the dust produced! and all the steam! and all the gases other than steam! and all the heat! and all the melt!) - it's just the only one that seems to explain the sandy, salty, cross-bedded, spherule-bearing beds imaged by the first two rovers at both Meridiani and Home Plate, on opposite sides of the planet. It also predicts that similar salty, cross-bedded, spherule-bearing beds could be found at the surface by later rovers (HiRISE imaging, as did earlier MOC imaging, suggests such layers could be common). The most elegant and marvelously detailed Meridiani hypothesis (vanished, highly acid playa lake/wind/soaking acid water/more wind/more soaking acid water/deep flowing - but never standing - concentrated acid brine/magically-diluting-and-mixing water), even if you ignore all of its special assumptions and internal inconsistencies (such as why cold water crystallized the high temperature, blue-gray form of hematite, and why that hematite should be enriched in Ni, and why the soluble salts never recrystallized, and many more I haven't mentioned), at best predicts and explains nothing at all about anywhere else, not even about the almost identical appearing beds at Home Plate.

So when is someone going to give me a hard time about Home Plate? (Although I'm perfectly willing to try to revive more "dead grandmothers" at Meridiani, if I can... biggrin.gif )

--Dr. Don

Posted by: ElkGroveDan Jun 23 2007, 04:21 PM

QUOTE (dburt @ Jun 22 2007, 09:43 PM) *
For example, if Mars wind today can only erode a few meters per billion years, how could it have deposited nearly a kilometer of sediments at Meridiani?

I think it's more than a little disingenuous of you to assume constant rates of erosion over 3.8 billion years, in of all places, Mars. That Mars has experienced a history of varied atmospheric densities isn't even in dispute. Indeed I can't image your "surge cloud theory" working under present 6 millibar conditions unless you admit that atmospheric densities were higher in the past. And of course in that case we are looking at higher rates of erosion and deposition.

(I also believe that the .38g on Mars will contribute to a much stranger movement of particle masses than has occurred in the Cascades, but I'm not prepared to wade into that debate right now.)

Don, you have some interesting ideas and your theories are certainly contributing to the discussions, but a lot of this minuscule "evidence" you cite is a bit tortured. Sort of like finding a candy wrapper and declaring "children were here!" I think you've killed off more than a few grandmothers yourself on this thread.

Posted by: David Jun 24 2007, 12:53 AM

What does this "kilometer of sediments" refer to? Is that supposed to be the depth of the stratigraphy? How could we know it actually goes that deep?

Sorry for the ignorant question, I just feel I'm missing something here...

Posted by: dburt Jun 24 2007, 12:58 AM

[quote name='Shaka' date='Jun 22 2007, 06:12 PM' post='93253']
...your answer above has tended to skirt the issue of the laminated structure of the Burns Formation as it relates to impacts.
[/quote]

See my discussion of surge deposit textures that was posted after you wrote this. Fine laminations and low angle cross-bedding, presumably caused by shear, characterize many surge deposits, despite their rapid deposition. Early in Mars history, there seems no limit to how many distant impacts could have contributed to the layering, although one big one might have been enough. Unlike with volcanism, impacts can occur anywhere, anywhen, into any available target, from a variety of possible impactor types, and be of any size (up to destroying the planet). A single volcanic surge eruption can result in many meters of section, containing many dozens of layers, varying in character between dune-like and relatively flat-bedded, with some containing disseminated accretionary lapilli and some not. Kilbourne Hole, New Mexico is a famous example of such a deposit, with slopes that resemble Burns Cliff, and dune forms that Gene Shoemaker initially ascribed to wind.

[quote name='Shaka' date='Jun 22 2007, 06:12 PM' post='93253']
...explosive volcanism on Earth could produce laminated, even cross-bedded, sediments of a similar appearance, and I, for one, would agree entirely with such an alternate cause if there were a range of stratovolcanos evident on the margins of the Meridiani Planitia.
[/quote]

I am reduced to citing volcanic analogs because, to be frank, no one has seen a surge formed by an impact (except presumably the dinosaurs and pterosaurs, who didn't live to tell about it), on this planet or any other. Impact deposits on this planet (except the coarse fraction - commonly called suevite if it is glassy) are weathered and eroded virtually immediatedly, unless they settle on the ocean, in which case they are water reworked, resorted, and highly hydrated (the fragmentary record of Chicxulub, the dinosaur-terminating impact, is largely written in gummy clay pseudomorphs). Owing to its dry, cold, near-vacuum conditions for most or all the past 3.8 billion years, Mars may turn out to be the best place in the Solar System to preseve a record of impact processes on a planet with subsurface volatiles and an atmosphere. Volcanoes, on the other hand, on Earth explode almost every week or month somewhere, so surge processes can be observed, and deposits can be fresh and unaltered, plus older deposits are commonly preserved under a capping lava flow, scoria deposit, or ignimbrite (welded ash flow tuff). Stratovolcanoes, as you probably know from your use of the word, would not be expected anywhere on Mars, owing to the lack of plate tectonics (they generally form only above subduction zones), nor would Yellowstone Park caldera-type supervolcanoes, because there is no hydrous granitic crust for a mantle plume to melt. In any case, even if Meridiani were a record of such an eruption, we'd might never know it, because the surge beds would probably be buried beneath a much thicker layer of erosion-resistant ignimbrite (welded tuff).

[quote name='Shaka' date='Jun 22 2007, 06:12 PM' post='93253']
...But that is quite apart from the question as to whether bolide impacts could produce an accumulation of ejecta resembling the Burns Formation. Many of us have a real problem with that. Impacts do form layered ejecta, but generally not more than two or three layers per impact, and these layers are usually quite distinctive lithologically. I think there are about three detectable in the mid North American continent from the Chicxulub impact. The lowermost from the high velocity jets of ballistic ejecta, the middle from the fallback surge of the collapsing ejecta column, and the third from the slow rain of fine distal fallout re-entering the atmosphere globally.
[/quote]

Your guess is as good as mine - because, like all scientific hypotheses, ours an informed guess with considerable evidence to support it and apparently nothing impossible (like a little boy claiming his grandmother was an ant or an elephant instead of merely dead on a test day) against it. Chicxulub, for which a highly imperfect record is recorded in a few spots fairly close by, impacted into the sea, with a rock target of layered carbonate rocks and anhydrite, on a planet with a strong gravity field and a relatively dense atmosphere, so it may not be representative of Mars processes.

[quote name='Shaka' date='Jun 22 2007, 06:12 PM' post='93253']
...We can see scores to hundreds of layers in the lower parts of the Victoria capes. They are remarkably uniform in scale and appearance. Since a rain of meteorites would distribute more or less randomly over Mars, it is hard to credit that some would not land closer to Meridiani and produce much thicker (meter-scale) layers, as can be seen in the Caribbean environs of Chicxulub. It is hard to imagine that the coarser proximal ejecta would not appear anywhere in the series, excepting the Victoria ejecta at the surface.
[/quote]

Congratulations! You have put your finger right on the weakest aspect of the impact surge argument. This group is really as sharp as I'd hoped it would be! biggrin.gif I can answer you in several possible ways, none completely satisfactory. 1) Oppy has imaged only a small portion of the Meridiani layers, those at the very top, which, being the youngest, could have formed when impacting had tailed off, and been distant (its lack of coarse surface material was, after all, what moved it to the top of possible landing site choices - it's possibly a biased sample, in other words). Coarse ejecta or surge layers may lie below the layers exposed, or may even be exposed somewhere deep in Victoria. Such a finding (of coarse pieces) would still be ambiguous, however, because ballistic ejecta could in theory land anywhere on Mars, at any time, on top of any type of sediment (and dust could settle, but it wouldn't stick around, unless the surface were sticky). 2) Coarse surface ejecta has been found at each landing site to date (and at others abandoned from consideration when too many surface boulders were found). Also, coarse layers of boulders in the midst of fine layers have been imaged by HiRISE in various spots - as noted by Emily in the post that inspired me to stop lurking here about a week ago. Finally, in its rush to get to Victoria (and not get stuck again), Oppy by-passed several areas of coarse broken rock imaged at a distance by the Pancam. These appeared to be lag deposits, and could imply wind erosion of a coarse layer stratigraphically just above the layers now exposed. 3) Sand grains carried by the wind whipping across the plain of Meridiani would eventually plane off and erode any coarse ejecta, unless it were buried - look at what has happened to the coarse ejecta blanket of Victoria (I admit that, given the slow rate of erosion on Mars, this is kind of like my arguing to teacher that my third dead grandma had an unusual sexual preference for the time or my grandpa had a sex change operation). 4) Perhaps my best answer is to simply cite William K. Hartmann, in his marvelous 2003 book "A Traveler's Guide to Mars", as noting that impact into sand or soft sandy sediments is going to mainly scatter more sand. (I don't have the book here at home, but I believe he used the phrase "produce a kablooey of sand and dust" which is not a bad description of a turbulent surge cloud.) In other words, by the end of the late heavy bombardment, much of Mars may have been so beat up that many impacts were "beating a dead horse" in terms of producing coarse ejecta.

But hey, each kid (or hypothesis in this case) is allowed up to two dead grandmothers, isn't he? smile.gif This is only the first that I'm aware of. (Note, we can't allow two per author, because that would give the Athena Science team an unfair advantage, although, IMHO, they might have exceeded their allowance even with that unfair method of counting.)

[quote name='Shaka' date='Jun 22 2007, 06:12 PM' post='93253']
...In many ways this argument is analogous to that which you make for blueberries. How can there be so many, so uniform and limited in size range? Actually I have less trouble believing that a broad, uniform plain of well-mixed thin sand layers, as Meridiani may once have been, could, when exposed to brief episodes of uniform wetting with very limited supplies of slow-moving groundwater, produce a crop of very uniform concretions with very limited growth, before the Big Freeze-Dry stopped everything but the wind.

...Furthermore, the berry distribution through the evaporite is even, as might be expected from a growth process strictly confined by a limited supply of solute, rather than random or aggregated as might be expected for accretionary lapilli being tossed and hurled by the violent currents of an impact surge.
[/quote]

I obviously can't stop you from believing what you want, but I thought I'd already covered this in previous posts, to a certain extent. I've spent much of my life looking for signs of fluid flow (mainly of hydrothermal fluids) and so far none have been imaged at either landing site, IMHO. (White deposits in surface cracks don't count because, like white desert caliche in cracks, they mainly indicate capillary action of moisture near the surface - an expected finding in the presence of water-attracting, soluble salts.) On the other hand, I can go anywhere in the Navajo (or Page) Sandstones, cited by the MER team and Marjorie Chan as a Mars analog, and see that the distribution of hematitic concretions (all red-brown and never blue-gray, of various sizes and shapes, commonly clumped together in nodular masses) is related to brine mixing and flow - distribution along former water tables, along fractures, both cutting across and along specific bedding planes, sudden lateral terminations, etc.). This distribution bears no resemblance to that at Burns Cliff or elsewhere.

If you put a less dense brine on top of a more dense brine, as the MER team proposes formed hematite from jarosite, it will sit there essentially forever - diffusion is possible over at most a meter or two in a sandy aquifer (water-saturated porous, permeable rock). How thick is Burns Cliff, which appears to be "spheruled" throughout? If you inject a less dense brine into a more dense brine from below, it will simply rise to the top as a plume, and you have the same problem again. How do you uniformly mix such brines across an area the size of the state of Oklahoma? It shouldn't even be possible in one place. (I trust some hydrologists will back me up in this.) Besides which, as mentioned in previous posts, rocks so rich in soluble salts should become impermeable owing to recrystallization within a very short time of being immersed in a saturated brine.

In our 2005 Nature article, Knauth described how presumed layered impact spherules (altered accretionary lapilli, as for Chicxulub, about 5 mm in diameter, as for Meridiani) in Archean (oldest known terrestrial) layered rocks are widely and uniformly distributed across areas of South Africa and Australia comparable to the Meridiani hematite area. Therefore, impact still seems like a far more reasonable process than brine mixing to scatter uniformly tiny hematitic spherules across such a wide area. I would be willing to wager that, no matter where future landers might land, no hematitic spherules or small groups of spherules larger than could be supported in a turbulent surge cloud will be found. (Of course, Oppy may prove me wrong as soon as it enters Victoria, or it may find some shale layers suggesting standing water (or compressed loess, deposits of airborne-dust), but right now I'd be willing to bet against either possibility. Note: some exceptionally big hailstones, such as those in the US national news last week, are large enough to break car windshields. I suspect that the Meridiani "hematite hailstones" (if that's what they really are) may themselves represent an exceptionally coarse deposit, judging from their apparent uniqueness on the martian surface.)

[quote name='Shaka' date='Jun 22 2007, 06:12 PM' post='93253']
...I am sure that the MER team model for Meridiani leaves some questions unanswered, but I still think it leaves fewer than the impact or volcanic alternatives. I don't have the chemistry expertise to deal with those issues, but as I drive around the Meridiani Planitia, courtesy of my good friend Opportunity, I get the sense that this has been one of the quieter, more-peaceful corners of Mars for much of its history. It's been a nice place to sit and ponder. smile.gif
[/quote]

We weren't there 3.8 billion years ago, and neither was Oppy. Everything since has been pretty calm, perhaps, but no more so than across most of the rest of Mars. (As mentioned above, if it hadn't been a calm spot since then, Oppy wouldn't have landed there. Also, remember what Bill Hartmann said about a kablooey of sand likely obscuring part of the cratering record.)

BTW, please excuse any typos in this and several previous posts. These are proofread by no one, least of all me. I say that because doing these posts is an exercise like taking a very, very long essay exam, and I don't want you taking any points off for my poor proofreading. smile.gif (Writing essays is something I haven't had to do for 40 years or so, and back then it was all in longhand.) Lots of role reversal going on here, and this group has some potentially great professors! wink.gif

--Don

Posted by: dburt Jun 24 2007, 01:43 AM

QUOTE (ElkGroveDan @ Jun 23 2007, 09:21 AM) *
I think it's more than a little disingenuous of you to assume constant rates of erosion over 3.8 billion years, in of all places, Mars. That Mars has experienced a history of varied atmospheric densities isn't even in dispute. Indeed I can't image your "surge cloud theory" working under present 6 millibar conditions unless you admit that atmospheric densities were higher in the past. And of course in that case we are looking at higher rates of erosion and deposition.

(I also believe that the .38g on Mars will contribute to a much stranger movement of particle masses than has occurred in the Cascades, but I'm not prepared to wade into that debate right now.)

Don, you have some interesting ideas and your theories are certainly contributing to the discussions, but a lot of this minuscule "evidence" you cite is a bit tortured. Sort of like finding a candy wrapper and declaring "children were here!" I think you've killed off more than a few grandmothers yourself on this thread.


Elk Grove Dan - I didn't make up the rates of erosion - they were order of magnitude quotes (from my admittedly increasingly faulty memory) based on numbers published by Matt Golombek et al. for the MER landing sites, with Meridiani, if I recall correctly, being slightly faster than Gusev (it's not in a crater and the rocks are softer). In any case, no more than 10 meters or so ever removed from either rover site in nearly 4 billion years - sort of hard to get used to for we terrestrials. (Note that long term burial in, e.g., drifting sand, followed by recent erosion, could likewise minimize observed erosion.) The atmospheric density probably varied considerably, but it was still a near-vacuum (the difference is between hardly any and not much at all).

Most people who study Mars rampart craters believe that the presence of subsurface volatiles is more important than the density of the atmosphere, because the impact vaporizes its own local atmosphere (mainly steam) to make the turbulent flow called a surge. The greater density of the surge is provided by the particulates. A lower atmospheric pressure might allow the surge to run out further and faster, but also would favor more rapid steam condensation, meaning the surge would "run out of steam" (literally). This is the explanation offered by Wohletz and Sheridan in 1983 for rampart crater deposits as surge deposits (most others favored some sort of mud sploosh at the time).

The weak gravity of Mars presumably likewise enables longer runout distance for Mars surge clouds (other things being equal, which they never are), but such modeling is still in its infancy.

BTW, what if I had discovered that hypothical candy wrapper (Meridiani exposures, in this case) on the day after Halloween? (formed right after 3.8 billion years ago, in this case) And the ground was coverd with tiny footprints? (millions of little and big impact craters, in this case). Would you still think I was jumping to conclusions?

So please specify those "dead grandmothers". Shaka pointed out a pretty good one, I thought, related to an apparent lack of coarse material at Meridiani - can you point out a second or third implausibility (based on logic, like he did - not based on the way we might feel things ought to work on another planet, based on our terrestrial predjudices)? And remember, I should be allowed at least one more. smile.gif

Or better yet, specify some impossibilities. Then I can hand in my essay exam and get it graded. Thanks, Prof. rolleyes.gif

--Don

Posted by: centsworth_II Jun 24 2007, 04:31 AM

QUOTE (David @ Jun 23 2007, 08:53 PM) *
What does this "kilometer of sediments" refer to? Is that supposed to be the
depth of the stratigraphy? How could we know it actually goes that deep?

From satellite images of eroded terrain around the Meridiani
region in which hundreds of meters of layering can be seen.
Below are links to a couple of articles.

http://www.space.com/scienceastronomy/060608_themis_meridiani.html
http://www.psrd.hawaii.edu/Mar03/Meridiani.html

Posted by: David Jun 24 2007, 04:43 AM

QUOTE (centsworth_II @ Jun 24 2007, 04:31 AM) *
From satellite images of eroded terrain around the Meridiani
region in which hundreds of meters of layering can be seen.
Below are links to a couple of articles.


Great, thanks -- but how do we know that these layers are of the same type as the relatively short column we see at Victoria, formed by the same process -- which I gather is what Dr. Burt is claiming?

Posted by: centsworth_II Jun 24 2007, 01:07 PM

QUOTE (dburt @ Jun 21 2007, 08:28 PM) *
....Gene Shoemaker (who later became world famous for his studies of impact cratering)....couldn't believe the giant sandy cross beds (dune forms) he saw were caused by explosive volcanism either, and initially attributed them to wind action. (Even most volcanologists were making similar mistakes in that era.) Since then studies by numerous volcanologists (clued in by nuclear bomb tests, where surges and their cross-bedded deposits were first described) have documented that thin bedding, low-angle cross-bedding, high angle cross-bedding, dune forms, and ripple forms can occur in surge deposits, all features that excellently mimic wind or water deposition.

Are any of these "numerous volcanologists" coming forward to support the credibility of your claims?
You mentioned that the surge theory was considered "lunatic fringe". How can that be if the sorts
of things that Opportunity is seeing are well documented in surge deposits from explosive events on
Earth? Is there even much discussion about this going on in geological circles? Are there any that
privately say you have a point or even agree with you but do not want to "go public"?

I'd love to see an "is Pluto a Planet?"-style public debate go on even though that was about
terminology more than basic science.

Posted by: centsworth_II Jun 24 2007, 01:19 PM

QUOTE (David @ Jun 24 2007, 12:43 AM) *
Great, thanks -- but how do we know that these layers are of the same type as the relatively short
column we see at Victoria, formed by the same process -- which I gather is what Dr. Burt is claiming?

Dr. Burt would probably hope to see layers different from those seen in Victoria. Note the recent
exchange with Shaka (see below). Maybe MRO can get a closer look at those layers.

Shaka: "...We can see scores to hundreds of layers in the lower parts of the Victoria capes.
They are remarkably uniform in scale and appearance. Since a rain of meteorites would distribute
more or less randomly over Mars, it is hard to credit that some would not land closer to Meridiani
and produce much thicker (meter-scale) layers...."

dburt: "Congratulations! You have put your finger right on the weakest aspect of the impact
surge argument.... I can answer you in several possible ways, none completely satisfactory. 1) Oppy
has imaged only a small portion of the Meridiani layers, those at the very top, which, being the
youngest, could have formed when impacting had tailed off, and been distant (its lack of coarse
surface material was, after all, what moved it to the top of possible landing site choices - it's
possibly a biased sample, in other words). Coarse ejecta or surge layers may lie below the layers
exposed, or may even be exposed somewhere deep in Victoria. Such a finding (of coarse pieces)
would still be ambiguous, however, because ballistic ejecta could in theory land anywhere on Mars,
at any time, on top of any type of sediment (and dust could settle, but it wouldn't stick around,
unless the surface were sticky). 2) Coarse surface ejecta has been found at each landing site to
date (and at others abandoned from consideration when too many surface boulders were found).
Also, coarse layers of boulders in the midst of fine layers have been imaged by HiRISE in various
spots - as noted by Emily in the post that inspired me to stop lurking here about a week ago.

Posted by: centsworth_II Jun 24 2007, 01:40 PM

QUOTE (dburt @ Jun 23 2007, 01:43 AM) *
So when is someone going to give me a hard time about Home Plate?

Speaking for myself, I'm operating on a very intuitive level here, not having
much knowledge and no expertise in geology. The base surge hypothesis is
counter intuitive at Meridiani and so raises the most questions in my mind.
It was so simple to see things the way the MER team described it.

At Home Plate, things seem a lot more complicated, even for the MER team.
In the Columbia Hills, even Steve Squyres has mentioned the possibility that
rock alterations were the result of volcanic steam. I don't know if he would
include impact steam as an alternative. In any case, the formation of the
Home Plate area is hypothesized to be the result of violent processes.

It's less of a stretch from volcanic to impact hypotheses for Home Plate
than it is from water/wind to impact at Meridiani.

Posted by: dburt Jun 25 2007, 11:20 AM

QUOTE (centsworth_II @ Jun 24 2007, 06:07 AM) *
Are any of these "numerous volcanologists" coming forward to support the credibility of your claims?
You mentioned that the surge theory was considered "lunatic fringe". How can that be if the sorts
of things that Opportunity is seeing are well documented in surge deposits from explosive events on
Earth? Is there even much discussion about this going on in geological circles? Are there any that
privately say you have a point or even agree with you but do not want to "go public"?


You're pretty perceptive. Yes, many agree in private, but for entirely obvious reasons they don't want to stick their necks out. And my use of "lunatic fringe" can be thought of as a triple pun on 1) lunatic, 2) luna (no self-respecting Mars geologist would ever admit that Mars resembles the Moon in as many ways as it is different - might be bad for funding), and 3) Gerald Wasserburg's "lunatic asylum" lab at Caltech, which is where many of the Apollo samples were dated by the rate of decay of their contained uranium and other radioactive elements. There were two huge scientific surprises yielded by the Apollo program (not counting the expected result that impact rather than volcanism caused lunar craters). One was that returned lunar rocks were dry as a bone (unlike terrestrial lavas and other igneous rocks, which are relatively hydrous); this dryness and lack of much of a lunar core was later explained by the giant impact theory of the origin of the Moon (that the Moon was formed by a Mars-sized impactor that hit the early Earth a more-than-glancing blow).

The other was that all the lunar impact melts (a few other rocks were older, whereas surface lavas were younger) all seemed to have formed at about the same time, 3.9 to 3.8 billion years ago. The "lunatics" hypothesized a "lunar cataclysm" or late heavy bombardment, which had almost erased the record of everything earlier. The modelers of the time couldn't deal with such a unique event (they favored a geometric decay scheme, somewhat analogous to radioactive decay, so that half of the impactors would be swept up by the planets in a given time, then half of those remaining, then half of those remaining, and so on until 3.8 billion years ago - such a model couldn't handle a sudden huge increase in impactors very late in the game). Modelers, because they are held by most people to be "smarter" than observationists (who, I guess, are supposed to be robots like beloved old Oppy), commonly rule popular opinion in science, despite observational evidence to that contradicts their ideas (look up the history of determining the age of the Earth from cooling rates, or of what happened to Wegener's definitive field evidence proving "continental drift" in the 1920's for examples of the influence of modelers on scientific progress). More than 35 years late, the modelers have apparently caught up with those early Apollo results (which, because they could not be modeled, were not widely accepted then or later) - see, e.g., this balanced discussion by Jeff Taylor:

http://www.psrd.hawaii.edu/Aug06/cataclysmDynamics.html

The majority of traditional Mars geologists seem as yet unaware of the probability of a late heavy bombardment in inner planet history and its implications, some of which were noted in passing by Jeff. For example, he noted that the late heavy bombardment neatly explains why the oldest continental fragments known on Earth are about 3.8 billion years old, although he didn't mention that the Earth, with its much stronger gravity field, should have been hit by far more impactors than the Moon. Also not mentioned: Mars, all alone in its immediate region of the Solar System, and with a stronger gravity field than the Moon, probably was hit much worse too. Jeff does mention the possibility that catastrophic impacting could have caused catastrophic rainstorms on early Mars, thereby neatly explaining drainage networks on some of the oldest, most highly cratered areas of Mars. If such rains ever fell, many of the lower layers at Meridiani could represent water-reworked impact debris, stripped from the nearby highlands (that would help with the total thickness problem, which some have objected to in this thread - although the tendency of surge deposits to pond in lowlands works too, at least for me, with wind stripping fines from the nearby highlands). The impact surge hypothesis strictly applies to only the uppermost rocks at Meridiani, those imaged and measured by the rover (plus many similar areas imaged from orbit on Mars, plus, of course, Home Plate). The observed abundance of soluble Mg-sulfates and the lack of stream channels probably rules out much rain at that time (although it doesn't necessarily rule out cold frost or snow, which would tend to leach only chlorides - see my earlier post). The observations also come close, IMHO, to ruling out the magnificently detailed model arrived at by the MER team, as described in earlier posts (hey, at least we agree that it didn't rain and that the odd salt mixture requires transport from elsewhere). BTW, "model" is the operative word - not "discovery," as it was reported by the popular press, journals that should know better, and the freshman textbook I currently use. What was "discovered" was some salty crossbeds containing tiny blue-gray hematitic spherules, and even that discovery represented considerable interpretation of raw spectral and analytical data. [...Darn preachy old professor! Almost as bad as that guy on the Bad Astronomy website, 'cept he's younger...]

If impact on Mars is the proverbial "elephant in the living room" that no one wants to look at or mention (except for dating younger surfaces and determining possible depths to ice), wasn't there another tale involving an elephant and a group of blind men (or, aaah, was it a group of highly specialized distinguished scientists, each afraid of contradicting the other regarding his or her specialty, and golly, I can't remember how that story goes)? Or was it something involving a camel? If I can't remember any animal story (excuse me for mentioning it; in fact, I don't even remember mentioning it), then no reasonable person could imagine I meant any possible relationship to any real people, living or dead. Also, no animals were injured while I was writing this, I'm writing this at home, and the usual disclaimer regarding colleagues and employer. (There's certainly a lot to be said for anonymous posting. laugh.gif )

To summarize, yes, in private (definitely not for attribution) many say that they agree with us.

--Don

Posted by: dburt Jun 26 2007, 01:32 AM

QUOTE (centsworth_II @ Jun 24 2007, 06:40 AM) *
Speaking for myself, I'm operating on a very intuitive level here, not having
much knowledge and no expertise in geology. The base surge hypothesis is
counter intuitive at Meridiani and so raises the most questions in my mind.
It was so simple to see things the way the MER team described it.

At Home Plate, things seem a lot more complicated, even for the MER team.
In the Columbia Hills, even Steve Squyres has mentioned the possibility that
rock alterations were the result of volcanic steam. I don't know if he would
include impact steam as an alternative. In any case, the formation of the
Home Plate area is hypothesized to be the result of violent processes.

It's less of a stretch from volcanic to impact hypotheses for Home Plate
than it is from water/wind to impact at Meridiani.


Thanks much for taking the bait, albeit reluctantly. If I showed Pancam photos of Home Plate vs. comparably exposed areas of Meridiani to one of my classes, I much doubt they'd be able to tell them apart (currently, Pancam photos of the two sites are biased in favor of the spectacular cliffs of Victoria - infinitely nicer than any Home Plate exposures). Except for a few cm. of poorly sorted gritty material with spherules at the base (extremely typical base surge deposit, BTW - although for obvious reasons that term is not being used), the rest of Home Plate looks very much the same as Meridiani (including Victoria cliffs) in terms of grain sizes and bedding textures - lots of low angle cross beds, but no large dune forms. Unlike Meridiani (but like most landing sites), it's littered with coarse impact debris. It has no particularly obvious unconformity (prominent former erosion surface) relating putative early volcanic to later wind deposition. The evidence for Home Plate beds being volcanic is, as I understand it, 1) their salty and basaltic composition - also likely for any impact debris anywhere on Mars, and 2) a single apparent "bomb sag" supposedly formed because a large rock was tossed out of a nearby invisible volcano (so-called ballistic ejecta). Ballistic ejecta are even more typical of impacts, so this feature is hardly diagnostic and, if there had been a volcano nearby, I might expect to see several more bomb sags in an area of the size already imaged by Spirit (an erupting volcano that's sputtering explosively because of steam explosions is hardly shy about ejecta). Rapid lateral changes in mean grain size are also typical of surge deposits caused by such small steam explosions, so I'd expect to see the gritty layer get much coarser in one direction, and much finer in the other, if the rover were traversing it towards or away from the putative volcano (a possible test of the invisible volcano hypothesis).

The interesting rocks showing sulfates or silica-rich alteration are all apparently sitting on top of the Home Plate layered rocks - they don't seem to be an intrinsic part of the package. To me they could have come from anywhere, as impact ejecta, and represent a possible sample of a volcanic or impact-related hydrothermal system somewhere else. Our hypothesis would relate the acid sulfates, at least, to sulfide oxidation (as originally proposed by Roger Burns for Mars in general). In other words, the top of Home Plate resembles coarse dump material near an open mine, with the blasting having been done by impact rather than by chemical explosives. See, e.g., my 2006 "Mars and mine dumps" Eos article attached (member educational use).



In response to your earlier question about volcanologists who might secretly agree with us, BTW, there's one who wasn't afraid to say so (a volcanology grad student who simply web-posted his conclusion and then returned to his thesis). He arrived at the same hypothesis about the spherules as we did, at about the same time (March, 2004), although he wasn't considering impact processes. Here's what he said:

http://www.geo.mtu.edu/~ajdurant/mars_acclaps.htm

Note that he was NOT talking about the spherules at and near Home Plate, which weren't discovered until much later (the MER team IS calling those accretionary lapilli). He was talking solely about the initial imaging of blueberries in Eagle Crater. Sorry, I hadn't located the link last night.

Think of a Meridiani surface surge as a fast-moving "kablooey blast of steam and dust" (the correct quote from Hartmann, 2003, A Traveler's Guide to Mars, p. 272 - sorry for my faulty memory in the previous post) and you can perhaps understand why coarse material might be lacking there - sand need not indicate a passive or calm environment (e.g., Hawaiian beaches during a storm). Only mapping and imaging over a truly regional extent (far more that these two rovers are capable of) could reveal lateral grain size variations, radial erosional channels caused by a vortex, or other indicators of a specific source location.

Anyway, if Home Plate is from a local volcano ("hydrovolcanic" or "maar-related" in geojargon), Spirit should be able to discover lateral grain size variations and more bomb sags at the scale of the HP outcrop; if distant impact is responsible, no lateral size variations might be expected at such a scale, and ballistic bomb sags should be rare. Hardly definitive, but they're both basically the same process, from a different explosion source in brine-soaked basalt. (Definitive diagnosis of impact would require, e.g., instrumentation able to detect microshattering of minerals or ultra high-pressure phases, such as diamond. Imaging impact melt splash droplets - tektites - might offer a diagnosis too.)

Thanks for politely giving the old Prof. another excuse to be boring. wink.gif Feel free to be impolite, however. I can't but you can, and I'm still seeking intrinsic flaws in our reasoning.

--Don

 2006EO490002.pdf ( 196.9K ) : 1068
 

Posted by: silylene Jun 26 2007, 11:04 AM

QUOTE (centsworth_II @ Jun 24 2007, 01:19 PM) *
Dr. Burt would probably hope to see layers different from those seen in Victoria. Note the recent
exchange with Shaka (see below). Maybe MRO can get a closer look at those layers.

Shaka: "...We can see scores to hundreds of layers in the lower parts of the Victoria capes. They
are remarkably uniform in scale and appearance. Since a rain of meteorites would distribute more
or less randomly over Mars, it is hard to credit that some would not land closer to Meridiani and
produce much thicker (meter-scale) layers...."

dburt: "Congratulations! You have put your finger right on the weakest aspect of the impact surge argument.... snip....


I don't read this good forum often enough because basically I am too busy to dive into it. Centsworth brought my attention to this interesting thread. I am not a geologist, rather a chemist....

Because of a lack of direct observational data, I don't think that we know enough about the behavior of fine dusts lofted by meteorite impacts in the atmosphere, and how they settle out globally or regionally. I am not sure that volcanic dust clouds are a good model for metoeric dust clouds, because I think that the particle size distribution might very well be quite different, and this would affect rates of settling.

If the dust cloud spreads, it's density over a region should be rather uniform (except right next to the impact crater, where there are surges). I have wondered if dust clouds from impacts could slowly settle down from the martian atmosphere to give fine layers of approximately even thickness? Could dust devils disturb the top one or two layers enough to give a festoon-like pattern in cross-section? I don't know. I also don't have a good explanation for how the layers get cemented together (unless there is rain or subsurface moisture).

I read through this thread and the "surge" explanation seems unconvincing to me for the creation of so many fine layers.

Posted by: dburt Jun 27 2007, 04:29 AM

QUOTE (silylene @ Jun 26 2007, 04:04 AM) *
IBecause of a lack of direct observational data, I don't think that we know enough about the behavior of fine dusts lofted by meteorite impacts in the atmosphere, and how they settle out globally or regionally. I am not sure that volcanic dust clouds are a good model for metoeric dust clouds, because I think that the particle size distribution might very well be quite different, and this would affect rates of settling.

If the dust cloud spreads, it's density over a region should be rather uniform (except right next to the impact crater, where there are surges). I have wondered if dust clouds from impacts could slowly settle down from the martian atmosphere to give fine layers of approximately even thickness? Could dust devils disturb the top one or two layers enough to give a festoon-like pattern in cross-section? I don't know. I also don't have a good explanation for how the layers get cemented together (unless there is rain or subsurface moisture).

I read through this thread and the "surge" explanation seems unconvincing to me for the creation of so many fine layers.


Nice to get new questions from a new face and fellow scientist, and welcome to the discussion. As partly detailed in posts above, our "impact surge" (initially called "brine splat") hypothesis was offered as an alternative explanation solely for the sandy, salty, cross-bedded (mostly at low angles), spherule-bearing layers imaged by rovers at Meridiani and, considerably later, at Home Plate. It does not deal explicitly with post-impact dust deposits or distributions (which, as you note, are likely to be far more extensive, but much thinner and much less permanent, owing to wind action), or with near-crater coarse ejecta. Neither deposit type has yet been imaged by the two rovers (although we speculate that the crudely-layered, coarse, hilly material in Gusev could be impact coarse ejecta), and orbital observations, even the latest HiRISE images, yield ambiguous results (large cross-beds are visible in some layers, possibly indicating migrating dune or surge deposits, and visible boulder beds are likely coarse ejecta, although they could form in other ways (e.g., landslides near a slope, former glacial moraines, stream channel boulders, and so on). What "so many fine layers" are you referring to - those imaged from orbit or those imaged on the ground by the two rovers? (See earlier posts for consideration of the latter in surge deposits.)

Our hypothesis originated when the MER team announced that Meridiani was a windy, dried up acidic playa lake or some similar evaporitic occurrence, that the hematic spherules were concretions proving that the subsurface had been soaked in liquid water, and that liquid water had later flowed across the flat surface, making current ripples (somewhat obscurely called "festoons"). A later minor modification to this model allowed that the incompatible (mixed soluble with insoluble) salt mixture had been wind-transported and deposited from an unknown playa-like source (somehow presumed to lie under the present exposures), but the complex model was otherwise unchanged. We were from the beginning puzzled by the numerous contradictions inherent in this model, some obvious and some subtle. As obvious examples, why should water flow across a flat surface, why don't the spherules look or behave like actual concretions in their shape, size or distribution, why is the hematite in them the blue-gray high-temperature form (specularite) unknown from sediments or sedimentary concretions, why are the spherules distinctly Ni-enriched compared to surrounding rocks, why are there no crystalline clays or clay deposits (clay rocks called shales are, other than salts, usually the only sediments deposited in playas - and dusty Mars should be covered with shales wherever there was liquid water at the surface), why should the youngest (uppermost) rocks exposed on chilly Mars indicate such a distinctly non Mars-like environment (more like Death Valley, CA in summer), how could nature so uniformly mix different-density brines in the pore spaces of sandy rocks to produce the alleged concretions, and why did all this alleged acid liquid water leave no trace of itself in the form of discolorations along fractures, recrystallization of and permeability reduction in soluble salts, dewatering textures in the rocks, visible flow channels on the surface, dried up mud cracks in puddles, or any of the numerous other water features so typical of terrestrial deposits?

As a chemist, perhaps you can appreciate some of the more subtle geochemical contradictions. For example, in the spherules, why should the Ni correlate with Fe, given that Ni2+ cannot be oxidized in aqueous solution and therefore cannot substitute for Fe3+ in hematite during crystal growth from aqueous solution? In aqueous solution, it should should instead subsitute for (partition into) the similar-sized Mg2+ in competing phases such as the abundant Mg-sulfates or Mg-bearing amorphous clays (if present). Substitution for Mg2+ is always dominant where Ni2+ occurs in natural sedimentary laterite (an oxidized type of soil) deposits on Earth (that's one reason why Ni is an expensive metal - it's expensive to extract from clays). High temperature, non-aqueous Fe2O3 can allow Ni2+ substitution by incorporating defects into its structure.

Another contradiction is that the Meridiani deposits are reported to have very high Br/Cl ratios. This is almost impossible to do in a brine without extensive fractional crystallization of chloride salts such as NaCl. (The larger, very rare Br anion freely substitutes for the very common, smaller Cl anion, but it shows a slight preference to remain in solution as chloride salts crystallize. You have to crystallize an awful lot of salt to build up appreciable Br concentrations in the brine.) If Meridiani were an evaporite deposit enriched in Br, chlorides should be the most abundant salts; instead, they are only a minor constituent compared to sulfates. Where did all those chlorides go?

Another, more obvious chemical problem relates to the fact that, in aqueous solution, acids are readily neutralized by bases producing salts. The Martian ferric sulfate mineral jarosite (on Earth nearly always formed by iron sulfide weathering in a moist, oxidizing envrironment, usually a desert mine dump or oxidized ore outcrop called a gossan - Roger Burns suggested the same mechanism should operate on Mars) was held to have grown in an acid underground reservoir the size of Oklahoma, on a planet utterly dominated by finely divided basic (MgO,CaO, Na2O-rich), olivine-rich lavas (normally, basalt). The acid underground solution and the lava fragments should have neutralized each other immediately, as has occurred in all experiments performed under comparable conditions, and gelatinous clay minerals should have been a by-product. Such a persistently acid solution seemed impossible, on Mars or anywhere else (except an inert, clay-lined basin, which describes some small acidic lakes in Australia, or in a volcanic crater lake, where new acid is being added constantly). Acid mine drainage at Rio Tinto, Spain was the offered Mars analog, but sulfide weathering wasn't included in their hypothesis (although it is included in ours).

We therefore sought an alternative explanation also involving sandstone, spherules, and a salty brine, and immediately ruled out wind because it didn't account for the spherules, and couldn't erode or transport them besides. Surge deposition came to mind (owing to extensive 1970's field experience), inasmuch as it commonly produces bed forms resembling all of those imaged by the rover, and sandy deposits commonly contain steam-condensation spherules called accretionary lapilli. Although most of our experience was with volcanic surge deposits, those seemed unlikely at Meridiani for a variety of reasons (wrong magma type and plate tectonic environments for Mars, wrong scale, nothing volcanic in the vicinity, no overlying welded tuff, etc.), so that left impact surge to consider. Impact provided us a lot more theoretical leeway (any scale, any distance, any target composition, a variety of impactor types, any time up to the present). The closer we looked at the images, and the more data that was returned, the better that hypothesis seemed. It accounted for EVERY feature imaged and reported (and still does, including ones not considered by the MER team) and seemed to solve ALL of the geological and geochemical contradictions inherent in the MER team interpretation.

Of course, as a new hypothesis, it raised a few problems of it's own. The most serious one, astutely noticed by Shaka in this thread, was why were the Meridiani materials all sandy (where were the coarser fragments)? If the responsible impacts were all relatively distant or targeted sandy deposits themselves, that seemed surmountable (also, the total thickness of section exposed to the rovers was less than 10-15 meters, and was not necessarily representative of deeper deposits). Another one, which no one in this thread has yet mentioned, was why the Fe-rich composition of the spherules? On a planet where the lavas are 2 to 3 times as Fe-rich as on Earth, where the impactor could have been an iron meteorite, and where Roger Burns had proposed abundant Fe,Ni-sulfide magmatic sulfide deposits in the subsurface, this didn't seem to be a serious problem. Somewhat surprisingly, we haven't thought of any other serious problems (and that really worries me, which is why I've been asking for input in this thread). Some here have objected that individual impacts might produce deposits that were too thin (whereas you seem to be saying the opposite). With almost an unlimited number of impacts available between 3.9 and 3.8 billion years ago (so-called late heavy bombardment, discussed in an earlier post) and with impact cratering an important process right up to the present, thickness or thinness of the deposits hardly seemed a problem either.

Once the sandy, salty, cross-bedded, spherule-bearing deposits at Home Plate in Gusev were discovered, including even the imprint of a small ballistic impactor ("bomb sag"), we hoped the argument might be over. But no, the MER team decided that HP was a hydrovolcanic surge deposit related to an invisible volcano erupting explosively owing to reaction of molten magma with a subsurface brine (just as Meridiani was allegedly related to an invisible playa lake containing a subsurface brine). Why are most Mars geologists apparently so blind to impact cratering as an important geological process, for deposition of ejecta as well as erosion of craters? I can only blame it on their strongly terrestrial (or possibly lunar) bias. We certainly agree with them about the subsurface brine (the basic goal of NASA's "follow the water" mantra) - it's difficult to account for the salts otherwise.

We may well be wrong in hypothesizing that Meridiani, Home Plate, and many other finely bedded deposits imaged from orbit could be caused by impacts, but it seems simpler than hypothesizing a special, unique sequence of geological events for each area, especially if those events all depend on a geological influence or phenomenon for which there's no direct evidence (e.g., an invisible volcano for Home Plate, or an invisible playa lake for Meridiani). Impact craters can be seen everywhere on Mars, of all sizes and ages. Occam apparently stated "Occam's razor" (sometimes called the K.I.S.S. principle) in response to parishoners blaming everyday events in their lives on the influence of "invisible angels". Have we really advanced very much if we always need to call on the influence of invisible geological agents to make common rocks on Mars?

If you see a volcano, then look for lavas (or other types of volcanic deposits). If you see lava, look for a volcano (on Mars only after you've made sure it's not an impact melt, perhaps). If you see a crater, think about both coarse and fine ejecta, and what might happen to the fines on a planet with an atmosphere and subsurface volatiles. If you see sandstone, think about the many ways there might be to make sand, including both impacts and exploding volcanoes, and go on from there. Be willing to change your mind as new data and new ideas become available - that's the only way you'll make important scientific discoveries, even if it runs counter to human nature.

Sorry post this is, as usual, too long - I meant it as more-or-less of a summary essay, so you don't have to read all the posts that precede it. Also, I think I've said just about everything I have to say in this thread, unless new questions or new objections arise (I'm really hoping for the latter). Thanks.

--Don

Posted by: silylene Jun 27 2007, 02:53 PM

Don,

Thanks for taking the time for a detailed reply.

I was thinking that deposition of suspended dust clouds from impacts could give uniform thin layers, as we saw in Meridiani. However, I do not have a good mechanism for glueing these settling dusts down into a layer unless the substrate had a moisture content.

Or perhaps, the impact dusts settled down onto a very shallow lake, and left layers underwater as they settled below? And the festoons are ripples from wind driven flow? Sorry, I don't know enough geology to differentiate if one possibility is more likely than another.

However, I don't see how surges could have produces all the thin fine bedded layers of similar thickness we have observed at Meridani. If it were surges, I would have expected some layers to be very thick, some thinner, and some containing jumbles of debris of various size. We haven't seen this.

On your criticism of the Fe/Ni ratios on the spherules, you do bring up some good points. However, I don't see how a surge mechanism would create spherules of this composition either.

Same goes for the Br/Cl ratios - the high Br levels always struck me as 'odd'. I wondered if Cl salts are more friable and thus more likely to be blown away, or something like that. Preferential erosion of Cl slats would ultimately cause the Br salts to enrich. All that said, I don't understand how a surge mechanism would account for the Br/Cl ratios either.

Posted by: centsworth_II Jun 27 2007, 03:12 PM

QUOTE (silylene @ Jun 27 2007, 10:53 AM) *
On your criticism of the Fe/Ni ratios on the spherules, you do bring up some good points.
However, I don't see how a surge mechanism would create spherules of this composition either.

Also, I find it hard to see how the "berries" could form of a different material than the general
population of dust and grains present in the violent surge outflow. I can see them forming slowly
from later, dissolved, minerals as concretions, but how were the spheres differentiated from the
rest of the base surge materials almost instantaneously?

Posted by: dvandorn Jun 27 2007, 06:16 PM

In discussion of the blueberries, I fail to see how they could be accretionary lapilli (or anything similar) from within a surge cloud and also exhibit the dimple/stalk morphology that we see in many/most of them. I can see stalks forming if they are concretions that built up from small voids in the salty rocks, not in lapilli.

And we don't see them *ever* deforming the layers in which they appear, as you would imagine they would if they fell onto newly-formed layers in the salty rocks. They are embedded in a fashion which screams (to my eye) "concretions formed in place" and not "lapilli that fell onto these layers." They are not organized along specific layers, they are scattered like shotgun-shot all throughout the layered rocks. If they were lapilli that were just dropped onto the still-fragmented salt dust that was being deposited by a surge, you would also expect a *lot* of signs of turbulence in the layer deposition "downwind" (or "downsurge") of the blueberries, and we don't. We see them perfectly embedded in layers that are otherwise laid down quite flat. And if we also buy the theory that each millimeter-thick layer was laid down by a separate impact surge event (which I still have a hard time believing, since the layers are so uniform in thickness), and we know that the blueberries are significantly larger in diameter than the layers in which they are embedded, where is the turbulence we should see "downsurge" from blueberries emplaced by the last surge? I would expect fillets along the upsurge side of the berries, and hollows on the downsurge side, even if the surge flow was relatively slow and non-violent. We see absolutely no sign of this.

I wonder a bit, too, about the lack of shales being definitive proof against a watery environment. The Meridiani light-toned unit is very thick -- if there were simply not enough silicates (especially phyllosilicates) to form a significant amount of the depositional surface, we'd be looking at a large substrate which simply doesn't contain the constructional materials necessary to form impermeable floors (i.e., shales) for standing water. In which case, you'd be looking at standing water *only* when the water table exceeded the level of the surface. As the water table receded downward, it would simply flow through a unit of permeable salty rock all the way down to the base of the aquifer, which (in my thinking) would consist of clays or shales formed at the top of the unit that lies below the light-toned unit. Since *none* of that unit is exhumed anywhere that Oppy has visited, we can't judge on the lack of such materials on the top of the present surface.

Just because Mars may once have had liquid water doesn't mean it would necessarily have formed the same features such water might have created on Earth (like pervasive shales), especially if there are compositional differences in the materials that held the water. Conditions on a hypothetical "wet, warm" Mars would have been very different from conditions on a wet, warm (and teeming-with-life) Earth -- we always need to appreciate that the same water conditions on the two planets could result in some significantly different results when it comes to how rocks were created and altered.

Just my $.02... smile.gif

-the other Doug

Posted by: dburt Jun 27 2007, 09:58 PM

QUOTE (silylene @ Jun 27 2007, 07:53 AM) *
Don,

Thanks for taking the time for a detailed reply.

I was thinking that deposition of suspended dust clouds from impacts could give uniform thin layers, as we saw in Meridiani. However, I do not have a good mechanism for glueing these settling dusts down into a layer unless the substrate had a moisture content.

Or perhaps, the impact dusts settled down onto a very shallow lake, and left layers underwater as they settled below? And the festoons are ripples from wind driven flow? Sorry, I don't know enough geology to differentiate if one possibility is more likely than another.

However, I don't see how surges could have produces all the thin fine bedded layers of similar thickness we have observed at Meridani. If it were surges, I would have expected some layers to be very thick, some thinner, and some containing jumbles of debris of various size. We haven't seen this.

On your criticism of the Fe/Ni ratios on the spherules, you do bring up some good points. However, I don't see how a surge mechanism would create spherules of this composition either.

Same goes for the Br/Cl ratios - the high Br levels always struck me as 'odd'. I wondered if Cl salts are more friable and thus more likely to be blown away, or something like that. Preferential erosion of Cl slats would ultimately cause the Br salts to enrich. All that said, I don't understand how a surge mechanism would account for the Br/Cl ratios either.


Silylene,

Perhaps you should read some of the earlier posts - some of this has been discussed. As for dust, I'm not going to worry about as a sedimentary deposit until it is imaged. If there was ever standing water, dust falling into it should have yielded finely laminar shale, likewise not yet imaged (and a strong argument, in my mind, against arguing for standing or flowing water at Meridiani). The "festoons" are allegedly ripples that are utterly unique to water-driven (not wind-driven) flow, according to the claim, although very similar features have been imaged in surge deposits (see above posts), so I am unconvinced, and most of the ones allegedly imaged by Opportunity appear to be topographical artifacts of the downward viewing angle (bedding contours wrapping around small ridges and V-ing up cracks).

The fine laminae and shallow cross-beds typical of Meridiani are also very typical of surge deposits, even quite coarse-grained ones, presumably owing to shear between the very high speed turbulent particulate flow and the substrate. Consistent thickess of laminae may indicate consistent velocity of the passing surge cloud - in any case, it is also typical (as it is of comparable wind and water deposits caused by turbulent flow).

All impact spherules are caused by vapor condensation in a hot turbulent cloud. Specular (blue-gray) hematite typically forms in steamy volcanic fumaroles by condensation and reaction of volatile Fe-chlorides or other volatile Fe species, and this is a very similar environment to that in a steamy surge cloud. The Meridiani difference is that some other sticky condensate must have caused the hematite flakes to preferentially adhere to each other and other particles, and grow as a snowball does, until they got too large, and settled towards the ground, where they were incorporated into the rapidly growing sand deposit, commonly in disseminated form. I don't pretend to understand all the chemistry going on in a dynamic, disequilibrium system like an impact surge cloud. Present were plenty of volatile iron species, at least possibly two sources of Ni species (Fe,Ni impactor or subsurface Fe,Ni sulfides), and abundant volatile salts and steam, and what resulted after condensation and crystallization were "blueberries". I don't know the details. The important point is that their mineralogy (specular hematite), high Ni content, size limitation, perfectly spherical habit, enormous extent, and failure to be distributed along fluid passageways or mixing zones indicates that they cannot be concretions. Therefore they must be condensates, analogous to hailstones. There is no reason to expect their Fe/Ni ratio to match that in meteorites, BTW (contrary to a claim made by the MER team).

As regards Br/Cl, see the above post on salts. By our hypothesis, extreme fractional crystallization of chloride salts, yielding high Br/Cl in residual brines and the last crystallized salts, occurred long before the impact episode, owing either to downward freezing of brines in the regolith (our favored mechanism) or surface evaporation of brine lakes (too cold, by our thinking, although surface freezing followed by sublimation works). These Br-enriched brines or late salts were then available to be incorporated in the impact ejecta, and the brines, at least, could have flowed laterally quite far away from their parent chloride salts. Frost leaching would preferentially remove surface chlorides, leaving surface sulfates, as covered in our 2002 and 2003 publications.

These are very good questions, BTW.

--Don

Posted by: ngunn Jun 27 2007, 10:04 PM

QUOTE (dburt @ Jun 27 2007, 10:58 PM) *
Silylene,


These are very good questions, BTW.

--Don


Always flatter your inquisitor! wink.gif

Posted by: helvick Jun 27 2007, 10:25 PM

Fascinating stuff.

I'm a complete amateur in terms of the geology side of things so bear with me if I'm asking really stupid questions.

First I have a question for everyone about the MER team's hypothesis.
Can anyone explain where the water comes from and how it stays around? I could find the layering we see geneuinely plausible if this was a wide area fairly calm "shallow" sea with some depth of water acting as a fluid buffer to help create the relatively fine layering. My understanding is that the sea idea has lost favour and the hypothesis is now talking about periodic pools and mostly subsurface water. Does that mean that the hypothesis now describes a predominantly dry "dust"deposition process with water mostly seeping up from the subsurface and occassionally pooling. I'm still at a loss as to where the water actually comes from - where's the other side of the water cycle? The evaporation \ clouds \ rain bit? Or am I missing something?

Moving back to the impact surge hypothesis I have no problem visualising thin, uniform, laminar deposition of layers from impact surges - lots of distant (large) impacts should average out with wide ranging thin deposition at their edges which might be thousands of km from the impact - however I cannot see how accretionary bodies formed a la hailstones can fall out of the same sort of "distant edge of the surge" fluid and I really have a problem with the lack of any obvious small scale deformation of the layers caused by the impact of these things as they land.

To go somewhat further afield and across to Spirit I have been very surprised by what appears to me to be remarkably well sorted "piles" of dusty materials. Specifically the exposures at Tyrone and Gertrude Weise seem hard to explain using any process. How does that sort of sorting happen in an impact surge?

Posted by: dburt Jun 27 2007, 11:42 PM

QUOTE (centsworth_II @ Jun 27 2007, 08:12 AM) *
Also, I find it hard to see how the "berries" could form of a different material than the general
population of dust and grains present in the violent surge outflow. I can see them forming slowly
from later, dissolved, minerals as concretions, but how were the spheres differentiated from the
rest of the base surge materials almost instantaneously?


See my previous post. The "dissolved materials" in this case were dissolved in a very hot, unstable, turbulent, multicomponent vapor. As it moved away from the impact site, this gas expanded, cooled, and various constituents condensed (precipitated) out of it, in succession. The system was highly dynamic, and moving along initially at supersonic speeds, so different things were probably happening in different parts of the cloud at the same time, and reactions were getting "smeared out" over great distances (more than 100 km in the case of Meridiani). At the same time, particulate matter was dropping out, more or less in order of decreasing grain size (with extremely poor sorting initially), and getting rolled along the ground, and bouncing, and earlier deposits were getting sheared off, forming cross-beds. Not that different conceptually from a flash flood or an Arizona dust storm or a submarine turbidity current or an air-supported large landslide, except that it was mainly a hot gas, containing lots of dissolved vaporized rock, made dense by the particles within it, and probably moving much faster than any of the conceptual analogs. Accretionary lapilli in volcanic deposits do not do not usually deform the beds around them, because they were deposited along with those beds.

As a gas, despite its turbulence, the surge cloud couldn't support blueberries larger than a given size (about 5 mm at Meridiani - probably unusually large), which is why they are so well size sorted as well as spherical. Actual concretions are supported by a rigid rock matrix as they grow in a leisurely fashion from an aqueous fluid, and so they are unconstrained as to size (their size is controlled solely by when they nucleated and how fast iron in solution diffused towards the growing concretions). They may incorporate the matrix (if it is quartz sand) or replace it (as for chert concretions in limestone). Concretions commonly are rounded, if they grow in a rock of uniform permeability, or highly flattened if they grow in strongly bedded rock, or elongated in the direction of fluid flow, if the fluid from which they grew was moving. As they grow, they commonly clump together in large nodular masses or beds. See previous posts for more on their typical distribution in relation to brine mixing and flow. The Meridiani blueberries appear to exhibit no such special distributions, or appropriate size and shape variations, and their very limited clumping (in rare doublets or extremely rare tiny triplets) can be explained by their inherent stickiness as they grew in the cloud - or by postdepositional salt coatings where they touched once deposited. They are NOT concretions, no way, no how (unless you really, really want them to be, and then we are talking about a belief, not science wink.gif ).

The short answer to your question would be: because different minerals or fluids condense out of the expanding, cooling vapor cloud at different times, as controlled by physical chemistry. (But you know how I hate short answers. smile.gif )

--Don

Posted by: dburt Jun 28 2007, 02:20 AM

QUOTE (dvandorn @ Jun 27 2007, 11:16 AM) *
In discussion of the blueberries, I fail to see how they could be accretionary lapilli (or anything similar) from within a surge cloud and also exhibit the dimple/stalk morphology that we see in many/most of them. I can see stalks forming if they are concretions that built up from small voids in the salty rocks, not in lapilli.

And we don't see them *ever* deforming the layers in which they appear, as you would imagine they would if they fell onto newly-formed layers in the salty rocks. They are embedded in a fashion which screams (to my eye) "concretions formed in place" and not "lapilli that fell onto these layers." They are not organized along specific layers, they are scattered like shotgun-shot all throughout the layered rocks. If they were lapilli that were just dropped onto the still-fragmented salt dust that was being deposited by a surge, you would also expect a *lot* of signs of turbulence in the layer deposition "downwind" (or "downsurge") of the blueberries, and we don't. We see them perfectly embedded in layers that are otherwise laid down quite flat. And if we also buy the theory that each millimeter-thick layer was laid down by a separate impact surge event (which I still have a hard time believing, since the layers are so uniform in thickness), and we know that the blueberries are significantly larger in diameter than the layers in which they are embedded, where is the turbulence we should see "downsurge" from blueberries emplaced by the last surge? I would expect fillets along the upsurge side of the berries, and hollows on the downsurge side, even if the surge flow was relatively slow and non-violent. We see absolutely no sign of this.

I wonder a bit, too, about the lack of shales being definitive proof against a watery environment. The Meridiani light-toned unit is very thick -- if there were simply not enough silicates (especially phyllosilicates) to form a significant amount of the depositional surface, we'd be looking at a large substrate which simply doesn't contain the constructional materials necessary to form impermeable floors (i.e., shales) for standing water. In which case, you'd be looking at standing water *only* when the water table exceeded the level of the surface. As the water table receded downward, it would simply flow through a unit of permeable salty rock all the way down to the base of the aquifer, which (in my thinking) would consist of clays or shales formed at the top of the unit that lies below the light-toned unit. Since *none* of that unit is exhumed anywhere that Oppy has visited, we can't judge on the lack of such materials on the top of the present surface.

Just because Mars may once have had liquid water doesn't mean it would necessarily have formed the same features such water might have created on Earth (like pervasive shales), especially if there are compositional differences in the materials that held the water. Conditions on a hypothetical "wet, warm" Mars would have been very different from conditions on a wet, warm (and teeming-with-life) Earth -- we always need to appreciate that the same water conditions on the two planets could result in some significantly different results when it comes to how rocks were created and altered.

-the other Doug


Other Doug - Are you perhaps getting as chatty as me? biggrin.gif If so, real sorry for the bad example I'm setting. Your questions seem to consist partly of vague misgivings, but I'll try to respond anyway.

First, don't confuse the spherules themselves with postdepositional overgrowths of salts and post exposure wind reshaping (especially of the softer overgrowths).

The spherules in matrix at Meridiani look just like accretionary lapilli in volcanic surge deposits - they don't make "bomb sag" like depressions because they don't fall ballistically from the sky like hailstones. Instead, they gradually get too big for the turbulent surge cloud, especially as it expands and drops out particulate matter, and work their way lower until they are incorporated into the rapidly growing sediment accumulation. Drop a marble into a flash flood - is it going to drop ballistically straight to the bottom, or get swept along as part of the general mass movement, and then dumped out?

You don't see turbulence down-berry presumably because such a force would just cause the berry just to keep on rolling. I am not a sedimentologist, however.

Each thin layer was presumably caused by a passage of turbulence/erosion - you can lay down meters of thinly laminated surge beds in minutes, if the steam cloud is condensing and turbulent shear continues at the same time. Depending on shear conditions, other deposits might be massive (more of a dump-out). I repeat, however, I am not a sedimentologist - I just work with one, and I'm still learning.

The lack of shales presumably indicates lack of surface, open, standing water in a lake or puddle, not necessarily a lack of liquid water in general (other observations suggest no liquid water in general). I only say this because Mars is infamously dusty. (Dust on a frozen pond might keep on going, giving you minimal shale, however.) Caution - you might make shale-like beds by depositing a layer of dry dust (such as impact loess) and then burying and compressing it. More likely the dust would just erode, though.

The impermeable shale unit (playa lake beds) that you and the MER team presume underlies the salty beds at depth seems to violate a fundamental rule of geology, superposition (that younger rocks are always deposited on top of older rocks). You assume they are the same age, and yet everywhere the alleged shales must be covered by a thick layer of own alleged erosion products. This is conceptually difficult. (If 90% of Meridiani were an exposure of a playa lake, a source region, with gypsum dunes piled up only at one end, as at White Sands, NM, this might make some conceptual sense. How can you so completely and so thickly cover up your own source rock, though? I know you could do it with some highly improbable 2-step special assumptions, such as pile the dunes up at one end, reverse the wind direction, and spread the salty sand out without allowing it to pile up at the other end, but give me a break, that's just too special - that's worse than saying Grandpa had a sex change, as per the earlier discussion of too many dead grandmothers. More like saying Grandpa personally went to Mars with a rake. Also, salt grains (as opposed to quartz sand) in dunes are extremely soft, and cannot migrate far or long without being ground to dust.

If you want to believe that early Mars was an Earthlike warm, wet world, with babbling brooks, clear lakes, gentle breezes, clean air, and gentle refreshing rainstorms to keep the air clean, feel free, if it makes you feel better. The MER team apparently pictures it as a giant smelter complex and toxic waste dump, with sulfuric acid constantly raining down from the skies and dissolving your clothing and ponding in shallow yellow-brown dead pools and lakes. Neither of those is how I currently picture it though - my picture (at least for the period 3.9 to 3.8 billion years ago) is more like an extended nuclear battle taking place between Peru and Bolivia during an ice storm, with salty surge clouds sweeping across the cratered altiplano, dropping shiny little radiactive black spherules along the way.

The phase diagram for water (controlling whether you get ice, water, or steam) is invariant among the planets, and Mars has always been much smaller and farther from the Sun than Earth. Ice, not liquid water or acid, should normally have dominated the surface. Transient episodes of warming owing to impacts (with possibly some input from early magmatism and volcanism) plus dissolved salts in brines seem sufficient to account for the orbital and ground observations to date. Any more warming and there should be many more clay minerals, for one thing (whereas salts you can crystallize by freezing and/or drying). Ditto acid.

But that's just my take. You're welcome to your own. Mine is again based on Occam's Razor - try to keep your special assumptions (a.k.a. "dead grandmothers") to an absolute minimum.

--Don

Posted by: dburt Jun 28 2007, 04:43 AM

Whew! Getting a bit winded from replying on that other thread. smile.gif In looking at today's new MER downloads, I couldn't help notice what appear to be "festoon" or trough-type cross-beds in the middle of the cliff at Cape St. Mary. The easiest ones to see are just below the exact center of the image, with some more subtle ones above and to the right, just below a pale massive bed (they're small, so look carefully - it's wonderful image, with lots of bedding detail):

http://qt.exploratorium.edu/mars/opportunity/pancam/2007-06-27/1P235874485EFF85MYP2443R2M1.JPG

I wouldn't dare to comment on their possible significance, but can you see them? (They look similar to those imaged in Erebus Crater, on rock faces named Overgaard and Cornville.) What do you think of them? Am I utterly mistaken, as usual? wink.gif

--Don

Posted by: dvandorn Jun 28 2007, 05:30 AM

Yep -- I see what you're talking about. I have a little wonderment as to how much shock alteration might play a part in the interruption of layers within any of these blocks, but I certainly see cross-bedding in many of the rocks in the cliff face. And there are a few examples of the cross-bedding that the MER team has called festoons, yes.

-the other Doug

Posted by: marsbug Jun 28 2007, 11:56 AM

Forgive me for asking what may be a dumb question, but can the evidence for a northern ocean be squared with the view of mars as an ice ball? The evidence in question may not actually be of an ocean, but if it is then mars must have been warm and wet for at least part of its history, and if its not what is the simpler explanation?
Edit: I should make it clear that by 'evidence of a northern ocean' I'm referring to the traces of coastline around the northern basin, not any more subtle evidence for an ocean which I'm not aware of.

Posted by: john_s Jun 28 2007, 02:15 PM

Looks pretty real, and pretty impressive, to me- can't wait to get a closer look (though I guess it's too high up the cliff for Oppy to get a really close view of that particular example). I don't see much evidence for shock alteration of these rocks myself- I bet all those fine-scale structures are sedimentary in origin.

Cool!
John.

Posted by: djellison Jun 28 2007, 03:06 PM

I've merged this thread and the Victoria-Festoons thread. We only need the one thread on Don's alternate Meridiani hypothesis.

Doug

Posted by: dvandorn Jun 28 2007, 03:51 PM

QUOTE (marsbug @ Jun 28 2007, 06:56 AM) *
Forgive me for asking what may be a dumb question, but can the evidence for a northern ocean be squared with the view of mars as an ice ball? The evidence in question may not actually be of an ocean, but if it is then mars must have been warm and wet for at least part of its history, and if its not what is the simpler explanation?
Edit: I should make it clear that by 'evidence of a northern ocean' I'm referring to the traces of coastline around the northern basin, not any more subtle evidence for an ocean which I'm not aware of.

If Mars had developed salty oceans before the late heavy bombardment nearly 4 billion years ago, that might explain the amount of salt that is distributed all across the planet. Impact cratering is generally not thought to be a great horizontal mixer of material, mixing more vertically than horizontally (at least based on the lessons learned from the Moon), but the very magnitude of the LHB could have distributed salts from the bottoms of obliterated southern hemisphere salty seas all across the planet (especially considering how far-flung the LHB must have thrown salty water from these putative seas into the early Martian atmosphere).

I can also picture a Mars which has quickly lost much of its atmosphere after the magnetic field died, cooling drastically, losing much of its liquid water to evaporation and ice sublimation and exposing tens of thousands of square kilometers of salty seabed; winds may then have eroded these salt flats and distributed the salts across the planet. So you don't necessarily need the LHB to explain the ubiquity of salts on Mars without requiring the entire planet to have been covered with salty seas, but it remains one plausible transport mechanism.

If there was a Great Northern Ocean, I'm thinking it must have post-dated the LHB, since there is no reason to believe that the impact flux would have limited itself to the southern hemisphere. I truly believe that, at the end of the LHB, Mars looked pretty much like the southern hemisphere looks today, but all over. The smoothed terrains we see in the north must have been overlain over a rough lunar-highlands-type of terrain, unless you want to try and explain how such a heavy bombardment could have completely missed one whole hemisphere of the planet... (Just trying to apply Occam's Razor, here.)

Nonetheless, it's important to remember that Mars with a thicker atmosphere and any kind of greenhouse effect would have been considerably warmer than it is today -- if you moved the Earth to Mars' orbit, it would be somewhat cooler but generally habitable (our seas and oceans wouldn't all freeze over, etc.). It's a touch disingenuous to suggest that Mars could never have been warm and wet because of its distance from the Sun and the related lower insolation than that received here on Earth. Mars is cold and dry today primarily because it lacks a magnetic field and thus the solar wind has sputtered a major percentage of its original volatiles right off of it. Had Mars not lost its magnetic field early on, it might still be warm enough and have enough atmosphere to support liquid water on the surface.

-the other Doug

Posted by: dburt Jun 29 2007, 02:07 AM

massive inline quote removed. - Doug.

Great reply to the original question. I would add only a few comments. 1) Impact cratering on Mars is different from on the Moon, owing to the martian atmosphere and subsurface volatiles. Unlike on the Earth, a very complete record of early martian cratering has been preserved (including, we suggest, layered fine impact-derived sediments). 2) Subtle details of MOLA topography and, more recently, radar imaging has revealed that your Occam's Razor supposition about the LHB affecting the northern lowlands as much as the southern highlands is correct. The Northern Plains appear to be just as heavily cratered underneath. Therefore, deposits sitting on top must postdate the LHB (pretty obvious from their paucity of craters anyway). 3) If there was a Great Northern Ocean, presumably formed by outflow channel brines, it could well have been frozen over, with the ice rapidly sublimating, and still left shorelines visible from orbit. In any case, no implications for ideas about higher Meridiani or Home Plate.

4) Current atmospheric theory, as I understand it, is that something like 99% of any early atmosphere was lost by "impact escape" resulting from the LHB (although the authors of the encyclopedia article, here:
http://www.atmos.washington.edu/%7Edavidc/papers_mine/CatlingLeovy-revised-PDF2.pdf
do not seem aware of the LHB, and conventionally just assume a gradual geometric decay of bombardment rates between 4.5 and 3.5 billion years ago. A problem with this conventional Mars assumption is that, as I recall, astronomical models suggest a pretty clean sweep of the inner Solar System in only the first 50 million years.) After the LHB, the very little remaining atmosphere has extremely slowly been lost by other processes and this slow loss continues. Therefore, to assume a "warm wet Mars" AFTER the LHB is supposing something for which there's little evidence except the probably faulty models of the MER team at Meridiani (contrary evidence is abundant, including a lack of young clays, and fresh olivine on the surface). We can imagine earliest Mars to be whatever we like (e.g., with the beautiful Venus jungle maidens so much in vogue when I started reading science fiction), inasmuch as any evidence was pretty much wiped out by the LHB. (Personally, I imagine pre-LHB Mars, which probably existed from 4.5 to at least 4.0 by, as considerably wetter, but not necessarily a whole lot warmer, than present-day Mars.) Owing to the LHB, it really doesn't matter. Mars history, like Earth history, pretty much started with a clean slate at about 3.8 billion years ago - think of Mars at that time as "Post-War ruins". And of course, I think that many of the layered sediments of the highlands, including Meridiani, could be remaining wartime debris. (Without the contained spherules, and predominance of low-angle cross-beds, and other bedding features, I might say they could be wind-deposited instead. In either case, they couldn't have been soaked in liquid water.)

--Don

Posted by: dburt Jun 29 2007, 06:35 AM

massive inline quote removed. - Doug.

Before these great questions get lost...

I hesitate (but obviously not very long smile.gif ) to respond about the MER team's hypothesis, because it makes little sense to me either and I may be just a wee bit biased (so please feel free to correct me, as always in my posts here). Meridiani is not much of a topographic basin, and there are no early drainage networks or other signs of liquid water leading towards it or away from it (e.g., no alluvial fans or deltas near its edge, no exit channels) so they had to assume (at least in their second iteration) that acid, salty waters mysteriously rose out of the ground, forming an enclosed playa lake (now mysteriously vanished, although they seem to see no logic problems with having it still somewhere underneath - see my other post) that then evaporated to precipitate abundant salts at the surface, both highly soluble and nearly insoluble, and neutral and acid (jarosite). In evaporation of any real playa lake, the salts would form bathtub rings according to solubility, with the least soluble ones on the outside, but this problem was not explicitly considered, I believe. These salts were then mysteriously mixed with each other and with with some type of amorphous particle (not crystalline clays) to produce granular little "mudballs" which the wind picked up and deposited at Meridiani as cross-bedded dunes (evidence: there's a large, high-angle cross-bed exposed at the base of Burns Cliff, the so-called Lower Unit). The mysterious brine rose again, but this time it arrived perfectly saturated with all the salts involved, and with the correct acidity, so as not to dissolve anything (fascinating, but why didn't anything recrystallize?). While rising, these waters somehow penetrated the impermable bottom of the vanished old playa lake, if it indeed lay beneath the cross-bedded dune deposits. The acid, saturated brine then established a new, higher-level water table, and wind eroded any non-wet granules on top leaving a planar surface (called the Wellington Contact in publications; a general term in sedimentology literature is Stokes surface, named after the geologist who first described such planar surfaces in dune-derived sandstones). Mysteriously, this "Wellington Contact" is actually not planar, and has a big trough or scour cut out of it (I think ignored in publications) and, unlike in an actual Stokes surface, no muds were locally deposited in low, wet areas. Next, wind, in a fashion that's completely mysterious to me, brought in more salty "mudballs" from this vanished playa, which by now should have been deeply buried beneath the earlier dune deposits, only this time the wind deposited exclusively a relatively thick sequence of low-angle cross beds ("sand sheets") called the Middle Unit and bottom of the Upper Unit. Next, the mysterious, chemically convenient brine rose again, and sat until it had discolored the top of the middle beds at what was called the Whatanga Contact. This is claimed to be the capillary fringe of subsurface evaporation just above the water table (no such capillary fringe is evident at the lower Wellington Contact - I guess it's supposed to have eroded off).

Then the ever-mysterious brine, without dissolving or recrystallizing away the earlier capillary fringe, rose to the flat surface and flowed ankle- to waist-deep across it, making current ripples (the record of which is allegedly seen in cross section as "festoon"-type cross-laminations, little troughs). The fact that this mysterious brine, still saturated in all the respective salts so as not to dissolve any, would possibly have had the viscosity of syrup, is ignored. The latest iteration of the model (an abstract at the shortly upcoming Mars meeting in Pasadena) refers to "gravity driven, possibly unchannelized flows resulting from the flooding of inderdune/playa surfaces". Where this alleged flood originated from, where it went, how it flowed across a flat surface, how it joined isolated interdune areas without leaving channels, where the playa was, what happened after it stopped flowing, and so on are unspecified details. It must have immediately sunk mysteriously right back into the ground, else it might have formed shales or mud cracks or something.

Next a new brine arrived, differing in acidity or iron content from the previous ones, but still saturated in all the relevant neutral salts. This somehow mixed uniformly with any previous brines to make disseminated jarosite concretions uniformly throughout the entire section without leaving any other trace of its passage. All "concretions" were mysteriously the same shape (perfect spheres), were strongly size-limited, and never clumped together as nodular masses (as discussed in previous posts).

Then yet another brine arrived, less acid and more dilute, and uniformly mixed throughout the aquifer over an area the size of Oklahoma (this is impossible, BTW), altering the jarosite concretions to hematite (mysteriously, the blue-gray shiny or "specular" high temperature form, not explained), but leaving the jarosite in the groundmass unaffected, so that Opportunity could detect it. This new brine, or perhaps a different one (I've long since lost count, to be frank), dissolved away some of the larger salt crystals, leaving crystal-shaped hollows in the rock, but still not recrystallizing or dissolving any other salts. Then everything ended. Whew!.

I admit I haven't completely reread the jargon-packed original papers in making this off-the cuff summary of the published stratigraphic section (doing so makes me too dizzy), or the latest modifications, so I may have minor details horribly wrong, but perhaps you get the general idea. Possible perhaps, but not terribly plausible. It does make quite a detailed, elegant, and magnificent story, though - and it's all based on just 3 meters or so of sandy, salty, spherule-bearing, cross-bedded section in a single outcrop in Burns Cliff (plus the even thinner exposure in Eagle Crater). Remember that there are 800 meters or so of layered rock lying beneath these surface rocks. What other incredibly complex, magnificent stories lie in wait?


Back to impact surge, the gaseous-particulate turbulent mixture is a fluid, not unlike water or wind, but travelling at many 100's of km/hr velocity (at least initially). Owing to shear and steam condensation, it can deposit great thicknesses of finely laminated sediments in a very short time, as covered in a recent post (after your question). You don't need a separate impact crater for each layer in a surge deposit, any more than you need a separate windstorm for each laminar layer in a dune, or a separate flooding event for each layer in a stream deposit. All that's needed is turbulence and flow. I'll repeat this as many times as I have to. smile.gif (Although I'll also repeat that I'm not a sedimentologist.) Regarding the lack of tiny impact craters for each tiny spherule, I already covered that in a recent post too. Picture injecting a bunch of BB's and sand directly into the turbulent exhaust of a roaring jet engine. Are the BB's going to fall straight down, or go with the flow?

I'm not sure what you're referring to w.r.t. "piles of dusty materials" in Gusev. From posted images alone, most of the rocks of current intense interest over there (subsurface sulfates, high-silica rock fragments, etc.) seem to be sitting on top of (not to be a part of) the layered surge deposits of Home Plate. What they signify is an open question, perhaps irrelevant to the origin of Home Plate and nearby layers and spherules.

All for now. Thanks much for your questions.

--Don

Posted by: Shaka Jun 29 2007, 09:52 PM

Re post #86
Prof Don,
At the risk of inflicting on you a horrible typist's RSI, I will ask you for a little more specific detail regarding the deposits left by impact surges (your paragraph #6). Though I have delved extensively into the impact literature, I am not familiar with the "finely laminated sediments" produced by "shear and steam condensation", and I wonder if you can provide me with some paper references that describe these sediments, preferably with photographs, so that I can compare them with the Burns Formation. Thank you,
Cheers,
Shaka

Posted by: dburt Jun 30 2007, 12:18 AM

QUOTE (Shaka @ Jun 29 2007, 02:52 PM) *
Re post #86
Prof Don,
At the risk of inflicting on you a horrible typist's RSI, I will ask you for a little more specific detail regarding the deposits left by impact surges (your paragraph #6). Though I have delved extensively into the impact literature, I am not familiar with the "finely laminated sediments" produced by "shear and steam condensation", and I wonder if you can provide me with some paper references that describe these sediments, preferably with photographs, so that I can compare them with the Burns Formation. Thank you,
Cheers,
Shaka


Shaka,

Here's a basic reference on volcanic and nuclear explosion surges, by one of my co-authors, Ken Wohletz:
http://www.ees1.lanl.gov/Wohletz/Pyroclastic%20Surges.pdf
A bit technical, I'm afraid, and not the best quality reproduction, but plenty of classic references and diagrams (see, e.g., the sand wave variations on p. 259). If you locate any good references on terrestrial impact surges, please let me know, because they are virtually never preserved on land, and the ones deposited in the sea are altered and reworked, including the spherules (so we are working by analogy from volcanic deposits, mainly). As stated in previous posts, there are plenty of reasons to suspect that Mars may be the best place to study impact surge deposits in the Solar System, and that the two rovers may have been imaging such deposits all along (including exposures in Victoria).

Ken's publications page, here:
http://www.ees1.lanl.gov/Wohletz/Publications.htm
has links to the above paper and many others, including the Wohletz and Sheridan 1983 paper in Icarus that first proposed that rampart crater deposits resulted from surges. I also attach a pdf of our 2005 Nature paper, which has some photos in addition to more discussion. Let me know if you need anything more.

--Don

 Knauthnature04383.pdf ( 529.75K ) : 666
 

Posted by: centsworth_II Jun 30 2007, 04:51 PM

QUOTE (dburt @ Jun 29 2007, 08:18 PM) *
Here's a basic reference on volcanic and nuclear explosion surges, by one of my co-authors, Ken Wohletz:
http://www.ees1.lanl.gov/Wohletz/Pyroclastic%20Surges.pdf

I'm struck by the pictures and diagrams that do look similar to what the MERs have seen.
I hadn't fully appreciated that this sort of material existed prior to the MER mission. It
gives the whole base surge theory a kind of predictive quality as opposed to reactive.

The picture on page 292 really struck me. The first I had ever heard of a volcanic "bomb" was
when the one at Home Plate was described. This picture looks like my second exposure to
a "bomb". Strangely though, I don't see specific mention of it in the text.

Here is the picture (top) with it's caption. The Home Plate image is below (not to same scale).

"A typical wet-surge
outcrop exposure described
by Sohn and Chough (1992)
showing irregular and scourfill
deposits and massive
bedded deposits. Photograph
from Sohn and Chough"

Posted by: CosmicRocker Jul 2 2007, 03:35 AM

Would someone please tell me where the "Festoons in cliff at Cape St. Mary?" thread went. I wanted to comment, but I can't find it. Was it merged with another discussion? blink.gif

Posted by: dburt Jul 2 2007, 04:00 AM

QUOTE (CosmicRocker @ Jul 1 2007, 08:35 PM) *
Would someone please tell me where the "Festoons in cliff at Cape St. Mary?" thread went. I wanted to comment, but I can't find it. Was it merged with another discussion? blink.gif


Yes. Doug moved it over to the "brine splat" thread in Mars, General, because it seemed to be casting doubt on prior interpretations of the intricate cross-bedding in the cliff. Please do comment.

--Don

Posted by: CosmicRocker Jul 2 2007, 05:37 AM

Thanks, Doc. smile.gif Doug does a great job managing this crazy place, but I wouldn't have moved those few comments into the brine splat discussion. I see small scale sedimentary structures in Cape St. Mary, and maybe some festoons.

I've been staying out of that brine splat fray because I would have to post tens of comments, but I have noticed that you are fighting an epic battle there. I don't know where you find the energy, but you do seem to be teaching a few folks that it is not easy to define the geologic environment of rocks that were formed on another planet several billions of years ago. wink.gif

I'm really having a difficult time fitting the impact surge concept to Meridiani, but I do agree that impact surge deposits should be relatively common in Martian rocks.

Posted by: don Jul 2 2007, 03:56 PM

Don - as a graduate of the ASU Geology Dept. (82) and former student of yours it's great to see Arizona State mentioned in the many recent contributions and discussions of mars. With Greeley as my advisor and the likes of Christensen roaming the halls, its hard not to look back and be proud of the accomplishments. I've sat in on a few of your presentations (and posters) over the last few years at meetings such as GSA and its humerous to see how fast you can raise the hackles of some of the MER team members. Your "mine dump" talk in Phily last year for GSA was especially interesting, Grotzinger if a remember correctly had a few "issues" to deal with. The mine dump analogy, while sounding off-beat, is right on in my opinion (but where is the sulfide). If anyone can think "out of the box" its Knauth and yourself, good luck with this idea. Personally, I'm more main stream, but I do have problems explaining the blended salts of Endurance.

Posted by: dburt Jul 2 2007, 08:55 PM

QUOTE (centsworth_II @ Jun 30 2007, 09:51 AM) *
I'm struck by the pictures and diagrams that do look similar to what the MERs have seen.
I hadn't fully appreciated that this sort of material existed prior to the MER mission. It
gives the whole base surge theory a kind of predictive quality as opposed to reactive.

The picture on page 292 really struck me. The first I had ever heard of a volcanic "bomb" was
when the one at Home Plate was described. This picture looks like my second exposure to
a "bomb". Strangely though, I don't see specific mention of it in the text.


Thanks for your comment on"reactive" vs. "predictive". Yes, the impact surge hypothesis predicts that spherule-containing, salty, cross-bedded deposits similar to those at Meridiani should be common on Mars, given that impacts (plus wind) have for the past 3.8 billion years or so been the only active geologic processes on Mars that could affect any area at random. In addition there were local major inputs from basaltic volcanism, a process that waned rapidly, but probably continues, brine flow at low elevations (outflow channels), a process that likewise seems to be continuing, at least at a very local scale (=young gullies - we predicted these should be highly enriched in chloride salts in 2002 and 2003), and glaciation (rock glaciers, especially), and perhaps others. More speculatively, if you accept the late heavy bombardment (LHB) scenario, the impact surge hypothesis also predicts that the kilometer or so of sediments beneath Meridiani might contain part or all of the sedimentary history (geologic record) of the near-destruction of a water-rich planet, including a record of impact-derived planet-wide rainstorms or snowstorms, if they occurred. The complex MER team hypothesis predicts little, inasmuch it appears to have been entirely reactive, applied only to that specific area and horizon, and required a sort of localized "Death Dalley Days on Mars" wet, warm scenario. (Of course, strictly speaking, the impact hypothesis was inspired by, and depended on rover images of those same horizons.)

Regarding vocanic bombs and bomb sags - they are highly typical of a certain type of surge deposit, which is perhaps why the bomb sag in the photo wasn't specifically mentioned. This type of "hydrovolcanic" deposit is caused by molten basaltic magma explosively meeting subsurface or surface water, and the volcano involved will usually toss out, via steam explosions, numerous solid blocks and blebs of molten lava (which blebs harden in the air to form a streamlined "bomb") at the same time it is making the surge deposit. If the particles are particularly wet and sticky, owing to an excess of water, the resulting surge deposit forms a distinctive conical "tuff cone," of which Diamond Head in Honolulu, Hawaii, is a fine example (the water involved was sea water). If ground water is less abundant, the steam typically just blows a crater ("maar") in the ground, surrounded by a more diffuse "tuff ring." Kilbourne Hole, New Mexico is a good example of this type of deposit. What puzzles me about the MER team calling "Home Plate" a tuff ring is that there appears to be no associated maar (i.e., no explosion crater) nor any tuff cone either. Also, if you see one bomb sag, you commonly see a dozen others nearby (whereas only one has yet been imaged). The "maar" type of surge deposit is usually quite limited in extent (a few kilometers across) with a rapid decrease in grain size from meter-sized blocks down to sand-sized particles as the distance to the volcano increases. The uniformly fine grain size of the Home Plate surge deposit suggests either that it all formed rather distant (meaning a few km) from the volcano, or it may be a different type of deposit. We suggest, of course, that it might be the erosional remnant of another impact surge deposit, with the single apparent bomb sag representing a hit by a piece of ballistic ejecta from an impact. Hopefully Spirit will last long enough to clear up that mystery, mentioned also in an earlier post.

Posted by: dburt Jul 2 2007, 11:44 PM

QUOTE (don @ Jul 2 2007, 08:56 AM) *
Don - as a graduate of the ASU Geology Dept. (82) and former student of yours it's great to see Arizona State mentioned in the many recent contributions and discussions of mars. With Greeley as my advisor and the likes of Christensen roaming the halls, its hard not to look back and be proud of the accomplishments. I've sat in on a few of your presentations (and posters) over the last few years at meetings such as GSA and its humerous to see how fast you can raise the hackles of some of the MER team members. Your "mine dump" talk in Phily last year for GSA was especially interesting, Grotzinger if a remember correctly had a few "issues" to deal with. The mine dump analogy, while sounding off-beat, is right on in my opinion (but where is the sulfide). If anyone can think "out of the box" its Knauth and yourself, good luck with this idea. Personally, I'm more main stream, but I do have problems explaining the blended salts of Endurance.


Other Don - Thanks for the minor vote of confidence. I'm certainly not trying to raise anyone's hackles, just get a word in edgewise with an alternative, more logical, and possibly more useful interpretation of the very same data. Your question "Where are the sulfides?" (to form jarosite) is an excellent one and I'd rank it right up there with Shaka's "Where are the coarse ejecta?" (as you might guess, we've asked ourselves the same questions). Some of the possible answers I've come up with include the following: 1) Mine dump-type damp, oxidative weathering can dispose of most iron sulfides within 50-100 years or less (usually with help from microbes); Mars has had nearly 4 billion years to get rid of sulfides at the surface. 2) Minor sulfides have been found both in Mars-derived meteorites and, I believe I've read, by the Spirit rover. 3) Roger Burns suggested that the sulfides would be magmatically concentrated in massive deposits of Fe,Ni sulfide at the base of lava flows or in magma chambers; impact would shatter or melt or vaporize these, so that survival in the surge deposits would be unlikely. 4) Rather than the little cubes that pyrite (fool's gold, FeS2) leaves on many terrestrial mine dumps, the main sulfide mineral involved on Mars would probably be pyrrhotite-pentlandite or (Fe,Ni)S, which phase generally does not form well-shaped crystals. Weathered-out pyrrhotite blebs in lava might be easy to mistake for gas-bubble type holes in lava. 5) The jarosite reported from Meridiani could previously have been reworked multiple times via multiple impacts, after moist oxidative weathering formed it - so that all signs of its parentage have been lost. 6) Jarosite could also form from oxidized sulfur species (mainly SO2) in the damp impact surge cloud - it need not have a sulfide precursor, except perhaps at the impact site. In presuming sulfide weathering, we were merely following the original "gossan hypothesis" of Roger Burns, as modified for impact. Leave the sulfides out, if you prefer - the impact surge hypothesis does not depend on them.

There! Is that enough sulfide excuses for you? laugh.gif

Regarding my "mine dump" talk at the Geological Society of America Meeting in Philadelphia last fall, the MER team member in question stood up at the end, in front of a large number of witnesses from the Planetary Geology Division, and tried to heckle me, by loudly proclaiming that he and SS had never stated that there was a shallow sea or lake at Meridiani, and that I should "stick to what was published in peer-reviewed literature". I mildly replied that I thought I had. After getting back to Tempe I naturally looked up the original 2004 Science article by Squyres, Grotzinger, et al. and on p. 1714 I found "the area on which these aqueous sedimentary and diagenetic processes operated was at least tens of thousands of square kilometers in size" and "Terrestrial analogs...include...playa lakes and sabkhas adjacent to marginal seaways." If that isn't an extremely strong implication (if not direct statement) of shallow seas or large lakes, I don't know what is. Therefore, one can hardly blame Science reporter Richard Kerr (who at the same meeting had just won the GSA Public Service Award for his excellence and accuracy in science reporting) for inferring only two weeks after the original publication (Science, 2004, p. 2010) that they were talking about "the salty, rippled sediments of a huge shallow sea" when Science Magazine declared this "discovery" to be its 2004 Breakthrough of the Year. Did Grotzinger mean to imply that reporter Kerr and the distinguished editors of Science Magazine were utterly mistaken? If so, he did not correct them. Of course his outburst was irrelevant to the main point of my talk, that no reservoir of liquid sulfuric acid of any kind was likely on a basalt-dominated planet (simply because bases neutralize acids in aqueous solution).

This initial 2004 "by the seaside" (or lakeside) iteration of the Meridiani hypothesis in Science was by 2005 replaced by the familiar "bouncing aquifer" version in Earth and Planetary Science Letters, in which the unlikely salt mixture had been wind transported from an original vanished playa or sabkha and then various brines conveniently rose in stages from underground, flowed vigorously across the horizontal sandy surface, and sank immediately back out of sight, meanwhile mixing freely, as required, with various other brines underground to make concretions and dissolve larger crystals (or at least that's my possibly faulty understanding of the basics of the current hypothesis, as summarized in my earlier post). Hey, if the initial interpretation was refined as new data became available, why was that something to deny at GSA?

Posted by: CosmicRocker Jul 3 2007, 05:08 AM

Ok, I didn't want to get into this debate just yet, but I suppose I was asking for it by posting that relocated comment in the wrong thread. I'll start out by asking "why would the suggestion of festoon cross laminations observed in Cape St. Mary contribute to this argument?" It seems to me that it would be more difficult to explain such small scale sedimentary structures embedded within larger scale sedimentary structures with a surge model. My apologies, if I forgot something discussed earlier.

Posted by: MarsIsImportant Jul 3 2007, 06:25 AM

I agree with CosmicRocker.

Although I can see how evidence of Impact surge could be common on Mars, I hardly see it as the only one. IMHO the impact model doesn't fit well with Meridiani--particularly in isolation. There are simply too many signs of both wind and water type erosion and deposition on the these plains. The lack of course material and sulfides cannot be discribed as minor problems. The fact that high rates of oxidation would be required for the surge process to explain what has been observed suggests massive changes in the Marsian environment every bit as complex and messy as anything that the MER team has proposed.

Let's face it. The Marsian environment has changed dramatically. The question is how. IMHO, the fact that massive amounts of water ice have been discovered in the subsurface and polar regions of Mars requires that when the KISS principle is used water in some form or another must have actively participated in the geology of part of the Marsian surface at sometime when the atmosphere was likely much thicker. IMHO, denying the impact of water based processes on early Mars would be a stretch of the imaginiation. There is simply too much of it.

With so many visible impact craters, it is also hard to deny the likely impact of surge processes over large parts of the surface. I just don't think one model alone can explain all the observations...when the evidence to supposrt any one model is marginal at best. All this combined highly suggests that complexity is closer to the truth. So in this case, the KISS principle when properly applied is not nearly as simple as we might want it to be.

Posted by: don Jul 3 2007, 03:04 PM

dburt - not that I’m a “brine splat” or “mine dump” groupie or anything like that but I do recall a question you asked following a MER member presentation at GSA in Salt Lake City a few years ago that raised some reflexive hackles. The question you asked was reasonable and the presenter responded quite persuasively with an explanation singing praises for eutectic brines (or something like that). Yet when you responded by the way (I paraphrase) I’m the one that introduced the concept of eutectic brines to mars the presenter realized who you were and immediately became defensive and curt. That moment for me stood out because it became evident (to no surprise) that it’s difficult being outside looking in when it comes to the MER project, if you don’t tow the party line you can be viewed as a non-friendly.

Regarding sulfide - in the recent (2007) Sqyures et al “Pyroclastic Activity at Home Plate in Gusev Crater Mars”, it’s mentioned that the rock “Fuzzy Smith” had a unique MB Fe mineralogy that’s consistent with a Fe sulfide such as pyrite or marcasite (evidently not detected in any other martian rock). Unfortunately the composition or oxidation state of the Fe was not determined and a sulfide confirmation could not be made. An interesting remark nonetheless.

the other don

Posted by: Kye Goodwin Jul 3 2007, 04:03 PM

Doctor Burt, Thanks very much for doing this. I have been defending the impact-surge explanation of Meridiani since late 2004 on another Mars forum. I have never been able to find out enough about volcanic surge from references on the net. That big technical paper of Ken Wolletz that you linked here adds much to what I have been able read on the subject but doesn't answer the following question.

In the Mer team Science publications of Dec 2004 single-particle layers were identified in the strata of Eagle Crater. I think that these were explained as an aeolian phenomenon affected by moisture. I have never been certain of this, but in some images of layered surge exposures that I have seen, it appears that single-particle layers are fairly common. I have never read anything that explicitly confirms this. Are single-particle layers a feature, maybe even a distinctive feature, of surge lamination?

Posted by: centsworth_II Jul 3 2007, 04:24 PM

QUOTE (don @ Jul 3 2007, 11:04 AM) *
...it’s mentioned that the rock “Fuzzy Smith” had a unique MB Fe mineralogy that’s consistent with
a Fe sulfide such as pyrite or marcasite (evidently not detected in any other martian rock)....

I remember that Steve Squyres expressed an interest in going back to Fuzzy Smith
when Spirit got back to Home Plate after the winter. But he specifically referred to
high silica content as the reason. This was before the discovery of "silica valley" so
I wonder if they would still make a point of going back.

Posted by: dvandorn Jul 3 2007, 04:54 PM

I was just thumbing through Squyres' "Roving Mars" again recently, and ran across something that I had thought I remembered.

For quite a good time (several weeks), Steve himself kept holding on to the notion that the layered rocks in the walls of Eagle crater were some type of welded tuff. As I understand it, Don is basically proposing that these rocks are, in fact, a form of welded tuff.

The vugs and especially the formation of concretions within the rock layers (as opposed to disturbing or displacing the rock layers) were the factors that changed Squyres' mind. That and the fact that the blueberries were of rather different composition (i.e., hematitic) than the rock in which they were embedded; the question that begs an answer is why *any* basal surge (volcanic or impact) would deposit simultaneously two populations of materials, each very different from the other. The compositional differences were sort of the nail in the coffin as far as Squyres was concerned.

Don, I don't think I've yet seen you address the question of why the blueberries would be so well distributed within the fine suplhate-rich layers and yet be of such different composition from them if these rocks were laid down by the same surge process. Wouldn't the mixing that occurs within the surge cloud, and the tendency for items of like mass to travel like distances (and of unlike mass to travel unlike distances) tend to sort out the gravels from the fines? An atmosphere would only tend to accentuate such sorting, I would think.

I just don't think we're seeing the kind of sorting one would expect between the heavy hematite-rich ferrous gravel and the sulphate-rich salt fines.

Also, how does the impact surge theory account for the apparent "feeder" formations into blueberries still in place -- small stalks of blueberry-like material leading in random directions from many of the in-place berries? These make sense if you picture the berries as concretions, formed by water flow within microfractures in the salty rocks. I don't have a feel for any inherent process in a surge that would account for them.

-the other Doug

Posted by: dburt Jul 3 2007, 09:44 PM

QUOTE (CosmicRocker @ Jul 2 2007, 10:08 PM) *
Ok, I didn't want to get into this debate just yet, but I suppose I was asking for it by posting that relocated comment in the wrong thread. I'll start out by asking "why would the suggestion of festoon cross laminations observed in Cape St. Mary contribute to this argument?" It seems to me that it would be more difficult to explain such small scale sedimentary structures embedded within larger scale sedimentary structures with a surge model. My apologies, if I forgot something discussed earlier.


CosmicRocker - Thanks for joining this discussion. Well, so far 3 people, including you, have chimed in agreeing with me that those look like "festoons" in the middle of the Cape St. Mary cliff, and none have disagreed, so apparently I wasn't, in my highly biased way, just seeing things. It has been claimed by a certain member of the MER team that these are an unambiguous record of little current ripples (like tiny sand dunes) that uniquely indicate water that was locally flowing vigorously ankle- to waist-deep across the flat surface of Meridiani. We have begged to disagree about the significance of these features, and even about their actual presence. Most look much more like a topographic artifact, caused by the downward viewing angle, as discussed in a previous post: Imagine yourself standing behind a person wearing horizontally striped trousers, and looking down at their posterior - you will see perfect "festoons" every time - UU.

The MER team, as far as I am aware, has been stating for the past 6 months or so that the cross-bedding in the Victoria cliffs uniquely indicates a record of aeolian (wind) deposition. Do you possibly see a consistency problem with having "festoons" in the middle? Does it in general sound reasonable to you that water (a sort of miracle brine) came gushing out of the ground, flowed ankle-deep to waist-deep across a level sandy interdune playa (an oasis among the dunes in the desert), leaving local little current ripples and absolutely no other record, and then sank back into that same reservoir? Can you explain why this artesian water flowing across water-saturated sand didn't simply form a braided stream deposit (dozens of tiny channels branching and rejoining as they flow leisurely across a plain), which is what 99.9999% of terrestrial streams would do under the same circumstances? Sorry for answering a single good question from you with so many more from me, but then I hope the answers to my questions are obvious.

The answer to your question is, no, I seen no problem with a huge variety of features, ranging from dune-like to ripple-like, occurring in a single cliff face that exposes surge deposits. The extreme turbulence (violence even) and rapidly changing conditions (including stickiness of particles) allow for far more variety than would be expected in a simple blowing-wind- or flowing-water deposit. The Victoria cliff exposures and their intricate, inconsistent bedding patterns therefore strike me as typical surge deposits.

Those so-called festoons are the only evidence ever cited for flowing water on this part of Mars. IMHO (as mentioned in an earlier thread), it's as unlikely to have such flowing water on a horizontal surface is it is was to have a puddle at a 20 degree inclination on Burns Cliff (as discussed prior to my participation here).

In deference to the other Don who started posting here before me, I'll henceforth refer to myself as

--HDP (for Herr Doktor Professor) Don tongue.gif

Posted by: tdemko Jul 3 2007, 11:11 PM

Like Tom, I've been lurking as this excellent discussion has progressed, but I now have to comment on what Don/"HDP" wrote in his last post regarding "festoons". As I've mentioned before, I never use this term, and it really has been out of fashion in clastic sedimentology for quite a while. We have better terms that more exactly speak to the scale and geometry of cross bedding and cross lamination.

What I see in the images in question of Cape St. Mary, at this distance, are large (meter) scale trough cross beds bounded by truncation surfaces. Other views of the other capes have also shown evidence of deflation or other more regional truncation.

What I interpret as having been called "festoons" in the past are either current or oscillation ripple cross lamination that is on the centimeter scale. Without better exposures that show more dimensions of these features, it will be difficult to definitively interpret their origin. The key features that I would like to examine would point to angle of climb, preferred current direction, foreset asymmetry etc. The clotty, recrystallized nature of the rocks in close-up photos of these features also makes "remote sensing" difficult.

Don Burt has provided some good references on the theory and some of the sedimentological features of base surge deposits, which include both cross lamination and cross bedding. However, bedforms are bedforms, no matter what the fluids and particles may be (channeled scablands to mud puddles). Allen's seminal work on the signal importance of flow separation phenomena on bedforms and resultant cross stratification is required reading for any and all interested parties, and Dave Rubin's visualizations are also very educational.

I am looking forward to even higher resolution close-ups of the Victoria cliff faces. If we start seeing grain-flow tongues and grain-fall drapes at the toesets of the large-scale trough foresets, an aeolian interpretation will certainly be preferred.

Posted by: dburt Jul 3 2007, 11:45 PM

QUOTE (MarsIsImportant @ Jul 2 2007, 11:25 PM) *
There are simply too many signs of both wind and water type erosion and deposition on the these plains. The lack of course material and sulfides cannot be discribed as minor problems. The fact that high rates of oxidation would be required for the surge process to explain what has been observed suggests massive changes in the Marsian environment every bit as complex and messy as anything that the MER team has proposed.

Let's face it. The Marsian environment has changed dramatically. The question is how. IMHO, the fact that massive amounts of water ice have been discovered in the subsurface and polar regions of Mars requires that when the KISS principle is used water in some form or another must have actively participated in the geology of part of the Marsian surface at sometime when the atmosphere was likely much thicker. IMHO, denying the impact of water based processes on early Mars would be a stretch of the imaginiation. There is simply too much of it.

With so many visible impact craters, it is also hard to deny the likely impact of surge processes over large parts of the surface. I just don't think one model alone can explain all the observations...when the evidence to supposrt any one model is marginal at best. All this combined highly suggests that complexity is closer to the truth. So in this case, the KISS principle when properly applied is not nearly as simple as we might want it to be.


MarsIsImportant - Thanks for chiming in. You haven't asked a specific question, which makes me uncertain how to respond. Perhaps I'll blather a bit, like you. smile.gif First, as I stated at the very beginning of this thread, please don't confuse me with Nick Hoffman and his "white Mars" scenario. As far as I'm concerned, you can have all the wind and water and climate change you like on Mars. Just be aware that surge deposits, in their considerable variety, can mimic nearly perfectly a huge variety of features generally described as being typical of (or even unique to) wind or water. Also be aware that, since the end of heavy bombardment (late or not), Mars scientists overwhelmingly agree that the dominant Martian climate has been very similar to that which we see today (with perhaps short excursions variously attributed to obliquity variations, underground brine outflow, volcanism, or impacts). The Meridiani "oasis" thus appears to be something of an anomaly, which is why it interests so many people. (Its high-temperature or "gray" hematite signature was an anomaly from orbit, which is why Oppy landed there.)

Our impact interpretation for the Meridiani (and Home Plate and, tentatively, other salty cross-bedded) deposits implies that they need not indicate either wind or water. No one argues that the soluble salts indicate water (a brine) in the past - the only argument is over when in the past. The impact hypothesis argues that the salts could be considerably older than the deposits in which they are found. After we had pointed out that the unlikely Meridiani mixture of salts that were both soluble and insoluble, and acidic and neutral was incompatible with a simple evaporation (playa or sabkha - marine salt flat) model, the MER team modified their model to include wind transport and mixing of older salts. (Then one of them, in what could be perceived as an attempt to heckle or intimidate me, vehemently denied having done so, in front of the entire Planetary Geology Division of GSA - as brought up by an eyewitness yesterday. A year earlier SS had argued to reporters that our Nature paper was worthless because we weren't aware of - and therefore didn't address - the latest changes to their model. Whom to believe? Did they make changes to their model or not?)

I won't argue with you that Mars is complex. Occam's Razor (or the K.I.S.S. principle) is useful only in deciding among competing hypotheses (preferably physical ones involving neither biology nor biochemistry), not as a general description of natural processes. You seem to be accusing me of misusing it. I don't think I am. Nevertheless, I'll freely admit that my personal prejudice is that Mars geology is probably considerably simpler than Earth geology (and more complex than lunar geology). The problem is that we all wear terrestrial "blinders" and cannot always recognize the stark, beautiful simplicity of Mars when we see it.

--HDP Don tongue.gif

Posted by: dburt Jul 4 2007, 01:54 AM

QUOTE (don @ Jul 3 2007, 08:04 AM) *
dburt - not that I’m a “brine splat” or “mine dump” groupie or anything like that but I do recall a question you asked following a MER member presentation at GSA in Salt Lake City a few years ago that raised some reflexive hackles. The question you asked was reasonable and the presenter responded quite persuasively with an explanation singing praises for eutectic brines (or something like that). Yet when you responded by the way (I paraphrase) I’m the one that introduced the concept of eutectic brines to mars the presenter realized who you were and immediately became defensive and curt. That moment for me stood out because it became evident (to no surprise) that it’s difficult being outside looking in when it comes to the MER project, if you don’t tow the party line you can be viewed as a non-friendly.
the other don


Other don - Thanks for the exact reference to the Spirit reporting of sulfides. It sounds like you were lucky enough also to be an eyewitness to my very first scientific encounter with the MER team member you mentioned in your last post, only a year earlier. After his GSA talk (which dealt with the team's new "vanished playa" modification to its earlier "playa" model - so I was quite aware of this modification well before its publication in Earth and Planetary Science Letters, contrary to claims made afterwards by SS) I asked the speaker, quite reasonably I thought, why the possibility of brine freezing was apparently excluded from consideration, given that Mars is such a cold planet (i.e., why the "Death Valley/Persian Gulf Days on Mars" story, instead of, say, making analogs of the permanently frozen, highly saline lakes of the Antarctic Dry Valleys). He replied, as I recall, that "because the brines are eutectic, we don't need to worry about them ever freezing". I was astonished nearly speechless by this statement, inasmuch as, 1) as I blurted out, Knauth and I had co-authored the 2002 Icarus paper "Eutectic brines on Mars..." which seemed to freak him out a little - at that time we had never met, and 2) he didn't seem to have the least idea how eutectic brines actually form. As I explained to him and SS in a later e-mail, by definition, the only way to make a eutectic brine is by freezing (or melting) - it is the last tiny little bit of brine left after fractional crystallization of all the solids, including ice and various salts (hey Ma, can you tell who'd been teaching igneous and metamorphic petrology for the previous several years? laugh.gif ). For the record, no reference to "eutectic brines" has ever afterwards found its way into the Meridiani literature, not even in meeting abstracts or talks. smile.gif

Sorry about telling that story (no Ma, really rolleyes.gif ). You gave me the obvious opening, and I couldn't resist. The utter misapplication of the term "eutectic" (I think he meant to say "all-salt saturated" or some such) certainly didn't inspire confidence in his infallibility as a sedimentologic super-authority. Nevertheless, rather than dissecting personalities (to which I'm as vulnerable as the next person), I'd really much rather keep this thread devoted to a semi-scientific dissection of that horrible, awful impact surge hypothesis, if you don't mind. As a starter question, are there any observed features of Meridiani that CAN'T be explained by that horrible, awful impact surge hypothesis?

BTW, Phoenix is supposed to get up to 116 F (47 C) tomorrow, for the holiday. Does that sound a lot like Mars to anyone?

--HDP Don

Posted by: centsworth_II Jul 4 2007, 02:10 AM

HDP Don,
It sounds like you are arguing that all the layers that Opportunity
has seen, and even that the entire 1km stack of layers, are likely
created by base surge events. Do you not allow for a significant
number of these layers being wind-blown deposits?

Posted by: centsworth_II Jul 4 2007, 02:52 AM

QUOTE (dburt @ Jul 3 2007, 09:54 PM) *
...are there any observed features of Meridiani that CAN'T be explained by
that horrible, awful impact surge hypothesis?

Going back to what you say in http://www.unmannedspaceflight.com/index.php?s=&showtopic=4308&view=findpost&p=93658
"All impact spherules are caused by vapor condensation in a hot turbulent cloud.
Specular (blue-gray) hematite typically forms in steamy volcanic fumaroles by
condensation and reaction of volatile Fe-chlorides or other volatile Fe species,
and this is a very similar environment to that in a steamy surge cloud. The
Meridiani difference is that some other sticky condensate must have caused
the hematite flakes to preferentially adhere to each other and other particles,
and grow as a snowball does..."

"[S]ome other sticky condensate must have caused the hematite flakes to
preferentially adhere to each other and other particles..."
sounds vague and
wishful. Is there any candidate for this "other sticky condensate"? The
"volcanic fumeroles" example sounds like something that takes time. I still
have a hard time seeing hematite berries forming in a violent, sudden event.
Has this sort of differentiation by condensation been seen in base surge deposits
on Earth or are most or all berry-like features in Earthly base surges similar in
composition to the material surrounding them?

My problem is with seeing such an efficient differentiation of materials ocurring in
such a violent, rapid, and short-lived event. I don't have a problem with differentiation
based on size, but with that based on chemistry. How was virtually all of the hematite
removed from the sulfate materials with which it must have been thoroughly mixed
by impact and recondensed as spherules so rapidly?

Posted by: dburt Jul 4 2007, 03:59 AM

QUOTE (Kye Goodwin @ Jul 3 2007, 09:03 AM) *
Doctor Burt, Thanks very much for doing this. I have been defending the impact-surge explanation of Meridiani since late 2004 on another Mars forum. I have never been able to find out enough about volcanic surge from references on the net. That big technical paper of Ken Wolletz that you linked here adds much to what I have been able read on the subject but doesn't answer the following question.

In the Mer team Science publications of Dec 2004 single-particle layers were identified in the strata of Eagle Crater. I think that these were explained as an aeolian phenomenon affected by moisture. I have never been certain of this, but in some images of layered surge exposures that I have seen, it appears that single-particle layers are fairly common. I have never read anything that explicitly confirms this. Are single-particle layers a feature, maybe even a distinctive feature, of surge lamination?


Hi Kye,

A web search revealed you as our only defender on that other site a long time ago. Nice to meet you at last and thanks for holding the fort, although I'd be especially interested in discovering why you decided to defend our highly controversial idea at such an early date.

Regarding your specific question about "single particle layers," not being or claiming to be a sedimentologist, I'm probably not the best person to answer it (but that hasn't stopped me yet - why now?). I'll give my reply in two parts: 1) I doubt that such layers could be unambiguously be recognized on MI images of Meridiani sediments, given the amount of salt encrustation. 2) Early Meridiani papers referred, I believe, to "pinstripe lamination" as being diagnostic of eolian deposits. We therefore looked up the original 1988 paper by Fryberger and Schenk in Sedimentary Geology, v. 55, p. 1-15. This referred to pin stripe laminations as "distinctive" and concluded only that "They may prove useful in the recognition of eolian sediments" in the abstract and "may help in identifying rocks of eolian origin" in the conclusions.

Once Knauth had published his first LPSC abstract here:
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1869.pdf
in which his Fig. 3 was labelled "Pinstripe lamination and low angle cross-bedding in base surge deposits from Kilbourne Hole, NM" the MER team apparently stopped referring to "pinstripe lamination" as proving anything much at Meridiani. Note also his Fig. 2 that shows a Burns Cliff-like high-angle cross-bed (dune-like form) from a surge deposit in the Superstition Mts. about an hour out of Phoenix, and his Fig. 5 that shows Meridiani-like polygonal cracking from a bedding surface at the same locality.

A better answer about "single particle layers" could perhaps be given by Tim Demko. I'm pleased to discover, from his latest post, that we have a real honest-to-God HDP sedimentologist hiding here amongst the sheep. Baaa. Baaa. Baaa. (He doesn't seem to think much of the term "festoon" either, and agrees that cross-beds indicate scouring - something that surges are certainly capable of, far more than the wind.)

--HDP Don

Posted by: dburt Jul 4 2007, 04:33 AM

QUOTE (dvandorn @ Jul 3 2007, 09:54 AM) *
I was just thumbing through Squyres' "Roving Mars" again recently, and ran across something that I had thought I remembered.

For quite a good time (several weeks), Steve himself kept holding on to the notion that the layered rocks in the walls of Eagle crater were some type of welded tuff. As I understand it, Don is basically proposing that these rocks are, in fact, a form of welded tuff.


Other Doug,

I'm running out of time to answer all of these questions tonight (my wife just called to find out where I am), so l'll try to be brief. Some types of tuffs are welded ("ignimbrites") usually from non-basaltic types of volcanoes. You wouldn't really expect welded tuffs on Mars. Volcanic surge deposits are characteristically non-welded (else they would never be mistaken for normal sediments), and impact surge deposits on Mars, where the target was probably frozen, could be expected to be even less so. The only welding is by salts, which encrust the grains during "diagenesis" (chemical and physical changes to a sediment that occur just after deposition) - that's also when the larger chloride crystals formed, later to be leached out (perhaps by frost). This encrustation does not require being immersed in water (in which case you would grow truly large crystals and segregate salts by solubility), only moisture and capillarity.

Regarding the hematitic blueberries, they theoretically could form in a number of ways (metal condensates, later oxidized, Fe-rich glass condensates, later oxidized, or Fe-rich accretionary lapilli, later oxidized). The only method that explains why they are the blue-gray or high-temperature form of hematite is if they actually grew in the surge cloud from Fe-chloride vapors and steam, as blue-gray hematite does in fumaroles. They probably condensed and accreted in the particle-poor, gas-rich top of the cloud, not the particle-rich bottom. Once they had reached a certain size, however, they gradually worked their way down through the turbulent cloud (still travelling at perhaps 100's of km per hour) and were deposited with the sand particles as a dissemination. Sorry if that sounds unreasonable to you. Make a better suggestion. Keep in mind that the conventional concretion story absolutely fails to account for the blue-gray nature of the spherules under any circumstances (or their strict size limitation, or their shape, or their failure to clump in masses) - and the blue-gray nature of the hematite in the spherules was the ONLY reason why Meridiani was picked as a landing site (other than being flat and equatorial). As I said in a previous post, picture yourself injecting BB's and sand in the turbulent exhaust of a screaming stationary jet engine (a crude approximation of a surge at some stage in its evolution). Do you really expect them to "sort out"? Read my earlier posts on this topic, and explain why a sedimentary concretion should consist of the high-temperature, blue-gray form of hematite.

As I also said in a previous post, don't confuse salt encrustations on top of spherules, or smoothing and shaping caused by wind, for the spherules themselves.

That's all for now before I have to get a divorce. Try to get to the rest later.

--HDP Don

Posted by: Kye Goodwin Jul 4 2007, 04:40 PM

Doctor Burt, Regarding your reply 108 and my 99: Why did I decide to support your outlandish theory early on? I guess I did something that few bothered to do. I found images of base-surge exposures on the net so I could see what you were talking about. The original brine-splat was not illustrated. Years later I am still answering variations on the objection that "An explosion couldn't produce regular layering", and that objection is apparently still a problem for some on this forum. I do not know HOW surge produces regular layering, and I suspect that this is not well understood by sedimentologists, but one can have no doubt that surge does often create regular stacks of layers if they just look at the pictures.

Also, I am a big fan of Occam. Your explanation isn't just a little simpler than the MER team's, it is an order of magnitude simpler.

I was not referring to pinstripe layering in my reply 99, but to single-particle layers be they thick or thin, that is, layers largely made up of particles with diameters that match the depth of the layer. I take your point that grains may not be reliably distinguished in MIs of the Meridiani sediments, but taking the MER scientists word for it, I have tried to find out more. Single-particle layers are apparently rare in sediments, aeolian sand-sheets being one of the few examples. I suspect that base-surge sediments and perhaps turbidites also hold single-particle layers but I have yet to read anything that discusses this question. I hope that we hear from sedimentologists. Could some of the regularity in thickness in some of the planar beds be contributed by a common large grain size? Are the layers shearing against each other at some time during deposition and being reduced to the minimum thickness that can hold the larger grains? It is a minor question perhaps with so much else to talk about, but the mechanism of surge deposition continues to intrigue me.

Posted by: dburt Jul 5 2007, 01:48 AM

QUOTE (centsworth_II @ Jul 3 2007, 07:10 PM) *
HDP Don,
It sounds like you are arguing that all the layers that Opportunity
has seen, and even that the entire 1km stack of layers, are likely
created by base surge events. Do you not allow for a significant
number of these layers being wind-blown deposits?


Centsworth - Thanks for the excellent question, which allows me to expound a little. No, I have no prejudice against eolian sandstones. In fact, some of my best friends are eolian sandstones. I've made their acquaintance in the Page area, AZ, over the past 3 years, and their names are the Page Sandstone and the lower down Navajo Sandstone. I've learned a lot from those friends, but not what the MER team claimed I might. See previous posts for some of what I've discovered about hematitic concretions, old water tables, flowing water, interdune playas, and so on.

On dry, cold Mars, as I see it, eolian sandstones have had a minor problem for the past 3.8 billion years at least. That problem is that it seems nearly impossible to form them. The basaltic sand forms with no problem (probably some or most of it was rock originally pulverized by impacts) but cementing it into a solid rock is the problem. That requires a long immersion in liquid water. Without that liquid water, the sand grains just blow around and and around, getting a little rounder in shape with each bounce, forming nice dunes, and filling craters such as Endeavor and Victoria partly or completely. The rounded grains act like little ball bearings (I credit Ron Greeley for this idea), making it easier for Oppy to get stuck, as already happened in Purgatory Dune and may happen shortly in Victoria (let's all hope not). If the sand gets buried deeply enough, or arrives near the poles, it may be incorporated into permafrost, but this sandy ice hardly a rock by conventional definitions - an hour in the lab and you'd have a pile of wet sand. Inasmuch as this is my own hypothesis, you will note that I am excluding from consideration the anomalous "Sahara desert oasis" hypothesized by the MER team for giant Meridiani (too many problems).

Well, you say, how do we make a sandstone then? Boom! of course. A big impact will dig up salts and vaporize ice, sending a super-hurricane force surge cloud out radially (with local little tornadoes leaving radial grooves, as described by Sue Kieffer and others for volcanic deposits). The cloud will efficiently scour away any sand or dust it encounters and incorporate it into the cloud - probably until the cloud eventually consists dominantly of such particles. The cloud will override mountains, efficiently scouring the highlands, and will eventually "pond" in a lowland, such as Meridiani or perhaps Gusev Crater, as it loses steam, literally. As salts and then steam condense the sticky sands are deposited (perhaps along with contained condensation-related spherules), and after a few post-depositional changes involving moisture and salts, voila, instant rock. The salt cement would never meet terrestrial construction standards - a little rain or snowmelt and it would rapidly fall apart, as happens to terrestrial impact deposits. On dry cold Mars these rocks seem to last for billions of years, however. In this regard, the famous Mars rampart craters were hypothesized to be erosion-resistant examples of abrupt steam condensation in relatively small and wet surge clouds by Wohletz and Sheridan (1983). The surge hypothesis thus accounts for the rounded sand grains imaged by Spirit's MI in the upper beds of Home Plate without requiring a separate eolian episode (mistaking surge for eolian deposits was the mistake made by Gene Shoemaker at Kilbourne Hole and other volcanic surge deposits in the late 1950's, before he had mapped Meteor Crater for his Ph.D. thesis at Princeton). The surge hypothesis also accounts for the many layered, salty deposits that fill old craters to above their rims (something seemingly impossible with water deposition).

I'm not saying that water- or wind-deposited sandstones might not occur in the lower levels of Meridiani (or in the Northern Plains) - I have no idea what torrential rainstorms or blizzards might have been condensing during the Late or other Heavy Bombardment, or what the transient weather might have been like. I'm just stating that in the 3.8 billion or so cold dry years afterwards, over the long term impact seems to me to be the only process capable of routinely depositing sandstones at higher elevations (absent drainage networks and outflow channels, that is, as at Meridiani).

I eagerly await HDP Demko telling me that there are a dozen other ways to make martian sandstones that I haven't considered. Please go easy on the technical vocabulary though - remember the audience.

BTW, Centsworth, why don't you tell your shy, insecure Australian buddy Jon Clarke to stop singing my praises on that other obscure site and get his two festoons ( UU ) over here ASAP (unless his enthusiasm has already caused him to be banned from this site). We HDP's have enormous egos that require constant stroking and I look forward to basking in his adulation. wink.gif Tell him I'll give him a penny for his thoughts. biggrin.gif

--HDP Don

Posted by: centsworth_II Jul 5 2007, 02:57 AM

HDP Don,
Tell me again why you're having trouble making friends
and influencing people in the scientific establishment? biggrin.gif

Posted by: Bill Harris Jul 5 2007, 03:54 AM

You're still wrong; in fact, so wrong that trying to convince otherwise is a wasted effort.

Posted by: CosmicRocker Jul 5 2007, 05:20 AM

I think some of you are being way too antagonistic. Do you not realize that we all have a special opportunity here to have a conversation with a scientist who publishes in major journals, and who is smack dab in the middle of a major planetary debate? How many other such researchers do you see coming out into the open, to publicly discuss their ideas so openly?

We are very fortunate that this forum encourages such communication. Personally, I disagree with a number of Dr. Burt's ideas regarding Meridiani, but others of his thoughts ring a bell with me. I think I will continue to sit in the back row and listen.

Posted by: nprev Jul 5 2007, 05:33 AM

Agreed, CR. While I am nowhere near knowledgable enough to participate in this debate, I treasure the fact that UMSF is a forum of choice for this dialogue.

And, just to reset the baseline here, let's not forget that Mars is an alien planet--not Earth--and alternative hypotheses to explain our obviously biased early observations should therefore be explored to the fullest. (Come to that, look at the full spectrum of gradual vs. catastrophic hydrological/stratigraphic events in Earth's geological record...who's to say that Mars' history is any less complex? Definitely insufficient data at this time to state otherwise.)

Viva free thinking, viva free exchange of opinions! Maybe it's just the US 4 July spirit speaking here (or other spirits, I confess... rolleyes.gif ), but, boy, is it great to see this sort of debate free of meetings, inevitable personal grandstanding/filibusters & ancilliary agendas. After all, what does Prof. B have to fear from all us Internet ghosts in terms of professional issues? Press on, gentlemen, press on! smile.gif

Posted by: Shaka Jul 5 2007, 07:04 AM

Whoa!! Careful, Bill. You're getting positively verbose! Sixteen words of dismissal, instead of just three. Next time you might even include an argument or two!
cool.gif

Posted by: Bill Harris Jul 5 2007, 07:12 AM

OK wink.gif

--Bill

Posted by: MarsIsImportant Jul 5 2007, 08:30 AM

QUOTE (dburt @ Jul 4 2007, 08:48 PM) *
Well, you say, how do we make a sandstone then? Boom! of course. A big impact will dig up salts and vaporize ice, sending a super-hurricane force surge cloud out radially (with local little tornadoes leaving radial grooves, as described by Sue Kieffer and others for volcanic deposits). The cloud will efficiently scour away any sand or dust it encounters and incorporate it into the cloud - probably until the cloud eventually consists dominantly of such particles. The cloud will override mountains, efficiently scouring the highlands, and will eventually "pond" in a lowland, such as Meridiani or perhaps Gusev Crater, as it loses steam, literally. As salts and then steam condense the sticky sands are deposited (perhaps along with contained condensation-related spherules), and after a few post-depositional changes involving moisture and salts, voila, instant rock. The salt cement would never meet terrestrial construction standards - a little rain or snowmelt and it would rapidly fall apart, as happens to terrestrial impact deposits. On dry cold Mars these rocks seem to last for billions of years, however....

...I'm not saying that water- or wind-deposited sandstones might not occur in the lower levels of Meridiani (or in the Northern Plains) - I have no idea what torrential rainstorms or blizzards might have been condensing during the Late or other Heavy Bombardment, or what the transient weather might have been like. I'm just stating that in the 3.8 billion or so cold dry years afterwards, over the long term impact seems to me to be the only process capable of routinely depositing sandstones at higher elevations (absent drainage networks and outflow channels, that is, as at Meridiani).


First, I like some of your ideas; but in the case of Meridiani, the evidence so far does not support your hypothesis. Another major problem is that the sandstones at Meridiani are MUCH harder deposits than what you claim would be created by an impact surge. The rover is fairly heavy. It has driven over these sandstone deposits many times. If they were as soft as you claim, then they would have crumbled. The only time the rover makes track marks is when it drives over loose or dune like crusty soil. The hard stuff underneath is a layered deposit that is not marked up unless the MER team uses the RAT tool. Your hypothesis does not account for its observed durability. If it were made as you suggest, then the RAT tool would have sliced through it like butter. The only possibility is that these hard layers were wet at some point.

In the second part that I quoted, you seem to be indirectly contradicting yourself slightly. If torrential rainstorms were possible, then why not directly at Meridiani? The Mars crust has shown through computer models to have significantly deformed with the shifting of the poles.

Low areas could easily gain altitude over the billions of years that passed. And if there was a lot of water, then capillary action could easily extend these dune like formations as they captured the blowing dust. Eventually the process would end and the formation of normal dunes on the surface would occur. Meters below the surface, the groundwater could easily morph the rocks further. Eventually the groundwater itself would either recede or freeze. With the water no longer in contact with the surface atmosphere, different types of brine could easily form over time depending on the circumstances. So far, we have an incomplete water record. We cannot be sure of all the circumstances. That's why it is so important for Opportunity to descend into Victoria as deep as possible. The best record should be revealed within days or weeks.

It's possible that that record will support your hypothesis; I just doubt it considering all that has been discovered up to now. I am willing to keep an open mind.

To change my mind, there must be a number of critical discoveries inside Victoria. The Pans of the inside of the crater suggests a similar story as the MER team has pictured. The story will likely change again slightly. But that is not a problem.

The MER team never stated how much water was on the surface. During interviews they stated the parameters were wide. When asked whether this body of water could have been a sea, they said it was possible but they didn't know. The press ran with the story that they found evidence of seas. Recently they simply narrowed the parameters. Their basic idea has not changed. You suggested that it had. That's why you got the confrontation. You seem to suggest that the MER team has not seriously considered the type of morphology that you currently propose. I would argue that they have and ruled it out. At times when discussing here you seem to have belittled their arguments--although I'm sure that was not your intent.

I appreciate your coming to this forum to discuss alternatives. Even if the evidence does not fit here at Meridiani, these ideas are still relevant. I particularly see possible evidence of what you are talking about at Gusev. The missing piece is Spirit finding a lot more examples of sulfides. Yet, even observed evidence at Gusev suggests further alteration after what appears Could have been impact surge.

Like I said, the story is complex. I personally don't think everything shut down after bombardment. I believe that Mars is dynamic even today. It is just not nearly as dynamic as Earth. Very recently and not necessary published, we are currently seeing the dynamic nature of Mars...the dust storms, the sudden change in the tracks with the sudden increase in wind (never before seen, until just days ago), the massive observed changes at Gusev with the impact of dust devils. Stuff moves around Mars a lot more quickly then we first thought. It just appears to happen in bursts.

Posted by: centsworth_II Jul 5 2007, 02:56 PM

QUOTE (Bill Harris @ Jul 4 2007, 11:54 PM) *
You're still wrong; in fact, so wrong that trying to convince otherwise is a wasted effort.

It would be helpful to the rest of us if you would pick a point that the professor has made,
either to disprove the MER team theory or support his own, and make your case against
it. HDP Burt may not be convinced, but the purpose of this type of forum is to educate and
convince the rest of us.

Posted by: djellison Jul 5 2007, 03:27 PM

QUOTE (MarsIsImportant @ Jul 5 2007, 09:30 AM) *
At times when discussing here you seem to have belittled their arguments--although I'm sure that was not your intent.


Unfortunately, despite all the science, it is this which stands out the most. Going on to belittle this place and those that visit it and run it was also totally unnecessary. It is a pity HDP feels the need to pitch his hypothesis this way, whatever its merits might be.

Doug

Posted by: ngunn Jul 5 2007, 09:29 PM

I've been watching this with interest but in silence (almost) so far. Doug, I understand why you are concerned - the discourse is rather one way. I would like to ask dburt (no fancy handles here) if anything at all has been gained by taking your ideas out for a spin on this forum? Have you heard it all before? If so, I think you should do us the kindness of withdrawing. We are not just here as hired devil's advocates.

BUT (and I hope this is the case) if in your view the discussion has been productive, i.e. has thrown up some new ideas, then I'd like to hear that. We are here I believe an open-minded and at the same time sceptical community, and I'd like to think we don't exclude ideas that challenge the consensus of the day unless we ourselves have the refutation to hand (as in the case of the water puddles). We don't just accept 'authority' - this is a separate court to the court of peer review, but I think it deserves respect in its own right.

Hope I'm not speaking out of turn . . .

Posted by: djellison Jul 5 2007, 09:35 PM

I'd agree with everything you've said there Nigel.

Doug

Posted by: dburt Jul 6 2007, 12:12 AM

QUOTE (djellison @ Jul 5 2007, 08:27 AM) *
Unfortunately, despite all the science, it is this which stands out the most. Going on to belittle this place and those that visit it and run it was also totally unnecessary. It is a pity HDP feels the need to pitch his hypothesis this way, whatever its merits might be.

Doug


Doug - I much regret if I have been giving the wrong impression. I have nothing but the highest respect for this forum, its outspoken members, and you as an exceptionally gifted and successful moderator. I've been reading this forum for years and I have always admired its free-wheeling debate on the merits and significance of various observations and ideas, including my own. I also have nothing but the highest respect for the MER team and all of its individual members, as highly trained, professionally distinguished scientists (else they never would have been chosen by NASA to be members of the team). If the MER team developed an unforseen problem, it was only that some of its members were perhaps TOO distinguished in their chosen fields (i.e., they may have been real HDPs, not total phonies like me). Nevertheless, they more than compensated, in my eyes, by placing all of the MER images and preliminary data interepretations on the web, thereby allowing all of us to see what we see and do what we do in close to real time. "Letting it all hang out" as they have been willing to do is perhaps the greatest breakthrough in planetary science ever, and I cannot praise it highly enough. I just cannot.

That's all besides the point though. My main point, as made in previous posts, and as some of you have politely made to me, is that when it comes to Mars, we all arrive wearing huge blinders. That is, we all have our biases and blind spots, derived from our professional and personal experiences, all of them so far on this planet, not Mars. My co-author Paul Knauth likes to say that Mars is nothing but a giant Rorschach ink blot, and that we all reveal ourselves when describing it. My biases are obviously drastically different from those of anyone on the MER team, owing to my background with volcanic surge deposits, and a long period of hopeless contamination with the ideas of ASU's late Robert F. Dietz, an iconoclast who spent the latter part of his life (once his ideas on plate tectonics had become scientifically acceptable) trying to convince other geologists of the importance of occasional large meteorite impacts in Earth history. My research specialties, other than the scientific study of mineral deposits, relate to the joys of exceedingly complex phase equilibria and crystal chemical interactions among minerals, so when it comes to Mars, many "pros" choose to dismiss me as an amateur, comparable to most of you. (And yes, I do have a mineral named after me.)

One other apology - science making, like sausage making, law making, and family feuding, is an extremely rough and tumble business, very different from its depiction in press releases, news stories, and freshman textbooks. It's also incredible fun, if you let it be. The way I have been speaking to you is no different (actually, far nicer - no use of "idiot" or "moron" for example) than the way we all speak to and of each other in the hallways of scientific meetings. I am deeply sorry if I have offended anyone with my unedited remarks or ironic sense of humor, or sounded patronizing, because that was not my intent. In compensation, I hope you have enjoyed this unique opportunity to witness and perhaps participate in a little of the real rough and tumble (and humor) of science. If you never think about a scientific press release or news headline in the same way again (e.g., "Scientists find cure for cancer"), then this little experiment in scientific communication will have succeeded. (Now in unison, class, all shout, "Show me the evidence!")

If I am allowed to continue on this forum, perhaps through mutual blinder removal we can arrive at original insights about what once happened on that utterly alien little planet, and have some fun doing it. Amateurs have always had an essential role to play in scientific discovery, and the modern science of geology itself is usually said to have been started by an amateur (Hutton, a Scottish physician). If not, it's been a real pleasure, and you all have inspired me to tremendous insights already. Thanks to you all, and thanks especially Doug for the chance (I was going to say opportunity, but ... smile.gif ).

--HDP Don

Posted by: dburt Jul 6 2007, 02:42 AM

QUOTE (centsworth_II @ Jul 3 2007, 07:52 PM) *
"[S]ome other sticky condensate must have caused the hematite flakes to
preferentially adhere to each other and other particles..."
sounds vague and
wishful. Is there any candidate for this "other sticky condensate"? The
"volcanic fumeroles" example sounds like something that takes time. I still
have a hard time seeing hematite berries forming in a violent, sudden event.
Has this sort of differentiation by condensation been seen in base surge deposits
on Earth or are most or all berry-like features in Earthly base surges similar in
composition to the material surrounding them?

My problem is with seeing such an efficient differentiation of materials ocurring in
such a violent, rapid, and short-lived event. I don't have a problem with differentiation
based on size, but with that based on chemistry. How was virtually all of the hematite
removed from the sulfate materials with which it must have been thoroughly mixed
by impact and recondensed as spherules so rapidly?


Centsworth - Vague and wishful it is, you got me. I wasn't there. We're just observing the possible results, and trying to explain them (we don't get to do this experiment in the lab). My candidate for "other sticky condensate" would probably be some sort of early-condensing salt or concentrated brine, but I'm open to suggestion. A large variety of spherically-shaped condensates and accretionary lapilli characterize both impact events and volcanic surge deposits, and they all are believed to form in a manner similar to hailstones in a thunderstorm - that is, by condensation. They aren't necessarily the same composition as the rock around them. Tiny native iron spheroids (condensates) surround Meteor Crater, AZ, for example, and that wasn't even close to the size or potential chemical variety of a good-sized Mars impact. What may or may not have happened at Meridiani is still open to debate, as you know. My "innocent" starting point was that those suckers sure don't look anything like real concretions, but they do look an awful lot like tiny hailstones (i.e., condensates).

Most people, including me for years, have real problems with surge deposition doing so much work in such a short time. Our geological training biases us in exactly the opposite direction (processes that take place slowly over millions of years). Nevertheless, high temperature gas-phase processes can occur extremely rapidly, and condensation is one of those processes. Volcanic fumaroles can develop and change extremely rapidly too (they are basically roaring steam jets). To separate the tiny hematite flakes from the rest of the solids, an earlier post hypothesized that hematite condensation occurred in the hotter, gas-rich upper part of the cloud, and that the "hematite hailstones" worked their way down to join the rest of the solids once they had reached a large enough size. Also, condensation really only had to happen in one narrow zone of the expanding, cooling cloud, and after that hurricane-force movement could scatter spherules over the whole of Meridiani. But again, I wasn't there, and am open to suggestion.

Great questions, as usual.

--HDP Don

Posted by: dburt Jul 6 2007, 03:01 AM

QUOTE (Kye Goodwin @ Jul 4 2007, 09:40 AM) *
Doctor Burt, Regarding your reply 108 and my 99: Why did I decide to support your outlandish theory early on? I guess I did something that few bothered to do. I found images of base-surge exposures on the net so I could see what you were talking about. The original brine-splat was not illustrated. Years later I am still answering variations on the objection that "An explosion couldn't produce regular layering", and that objection is apparently still a problem for some on this forum. I do not know HOW surge produces regular layering, and I suspect that this is not well understood by sedimentologists, but one can have no doubt that surge does often create regular stacks of layers if they just look at the pictures.

Also, I am a big fan of Occam. Your explanation isn't just a little simpler than the MER team's, it is an order of magnitude simpler.

I was not referring to pinstripe layering in my reply 99, but to single-particle layers be they thick or thin, that is, layers largely made up of particles with diameters that match the depth of the layer. I take your point that grains may not be reliably distinguished in MIs of the Meridiani sediments, but taking the MER scientists word for it, I have tried to find out more. Single-particle layers are apparently rare in sediments, aeolian sand-sheets being one of the few examples. I suspect that base-surge sediments and perhaps turbidites also hold single-particle layers but I have yet to read anything that discusses this question. I hope that we hear from sedimentologists. Could some of the regularity in thickness in some of the planar beds be contributed by a common large grain size? Are the layers shearing against each other at some time during deposition and being reduced to the minimum thickness that can hold the larger grains? It is a minor question perhaps with so much else to talk about, but the mechanism of surge deposition continues to intrigue me.


Kye - I appreciate your doing your own investigation of surges. Also I'm always glad to meet another fan of Occam. Regarding single particle layers, still not my field, sorry. Perhaps Prof. Demko can enlighten us? If not, I doubt if such claims for Meridiani are important to the big picture. (When all is said and done, those wonderful MER machines are still somewhat limited investigative tools. For example, their Pancams can't bend down to look at things sideways...)

--HDP Don

Posted by: dburt Jul 6 2007, 05:13 AM

QUOTE (MarsIsImportant @ Jul 5 2007, 01:30 AM) *
First, I like some of your ideas; but in the case of Meridiani, the evidence so far does not support your hypothesis. Another major problem is that the sandstones at Meridiani are MUCH harder deposits than what you claim would be created by an impact surge. The rover is fairly heavy. It has driven over these sandstone deposits many times. If they were as soft as you claim, then they would have crumbled. The only time the rover makes track marks is when it drives over loose or dune like crusty soil. The hard stuff underneath is a layered deposit that is not marked up unless the MER team uses the RAT tool. Your hypothesis does not account for its observed durability. If it were made as you suggest, then the RAT tool would have sliced through it like butter. The only possibility is that these hard layers were wet at some point.

In the second part that I quoted, you seem to be indirectly contradicting yourself slightly. If torrential rainstorms were possible, then why not directly at Meridiani? The Mars crust has shown through computer models to have significantly deformed with the shifting of the poles.

Low areas could easily gain altitude over the billions of years that passed. And if there was a lot of water, then capillary action could easily extend these dune like formations as they captured the blowing dust. Eventually the process would end and the formation of normal dunes on the surface would occur. Meters below the surface, the groundwater could easily morph the rocks further. Eventually the groundwater itself would either recede or freeze. With the water no longer in contact with the surface atmosphere, different types of brine could easily form over time depending on the circumstances. So far, we have an incomplete water record. We cannot be sure of all the circumstances. That's why it is so important for Opportunity to descend into Victoria as deep as possible. The best record should be revealed within days or weeks.

It's possible that that record will support your hypothesis; I just doubt it considering all that has been discovered up to now. I am willing to keep an open mind.

To change my mind, there must be a number of critical discoveries inside Victoria. The Pans of the inside of the crater suggests a similar story as the MER team has pictured. The story will likely change again slightly. But that is not a problem.

The MER team never stated how much water was on the surface. During interviews they stated the parameters were wide. When asked whether this body of water could have been a sea, they said it was possible but they didn't know. The press ran with the story that they found evidence of seas. Recently they simply narrowed the parameters. Their basic idea has not changed. You suggested that it had. That's why you got the confrontation. You seem to suggest that the MER team has not seriously considered the type of morphology that you currently propose. I would argue that they have and ruled it out. At times when discussing here you seem to have belittled their arguments--although I'm sure that was not your intent.

I appreciate your coming to this forum to discuss alternatives. Even if the evidence does not fit here at Meridiani, these ideas are still relevant. I particularly see possible evidence of what you are talking about at Gusev. The missing piece is Spirit finding a lot more examples of sulfides. Yet, even observed evidence at Gusev suggests further alteration after what appears Could have been impact surge.

Like I said, the story is complex. I personally don't think everything shut down after bombardment. I believe that Mars is dynamic even today. It is just not nearly as dynamic as Earth. Very recently and not necessary published, we are currently seeing the dynamic nature of Mars...the dust storms, the sudden change in the tracks with the sudden increase in wind (never before seen, until just days ago), the massive observed changes at Gusev with the impact of dust devils. Stuff moves around Mars a lot more quickly then we first thought. It just appears to happen in bursts.


MarsisImportant - That's a quite long quote, and perhaps it should get edited out, but I wasn't sure where to begin - you have a lot of interesting comments to make. Regarding the apparent hardness of the Meridiani rocks, remember that Mars gravity is weak, the Meridani cliffs are visibly crumbling, and the wind appears to have carved them like a knife. So they can't be all that hard. The RAT isn't necessarily a good indicator, because it's going to be stopped by the hard sand, not the soft cement (would you want to rub your face with butter-cemented sand, as opposed to butter?) Also, I've walked across plenty of volcanic surge deposits that formed in the proposed manner (steam condensation), and they were all about as hard. For strength, the rock cement, in addition to the salt mixture, probably contains much of the dust in the cloud. That makes it relatively strong, so long as you don't add much liquid water. Remember that - almost no liquid water since it formed. (Magnesium sulfate, apparently the dominant salt at Meridiani, is the most water soluble of all the common sulfates.) By our surge hypothesis, everything was once moist (or "wet" if you will), but never more than that - it never saw large quantities of liquid water, or it would have fallen apart. The MER team gets around this objection by special assuming that all of their hypothesized brines fortuitously were saturated in all of the salts present, but they apparently forget that even then, all of the soluble salts should recrystallize into large crystals (put some fine table salt in jars, add various amounts of water, and come back in a month - let me know what you see). I may have mentioned this in a previous post - I'm losing track now...

Regarding self-contradiction, in terms of the possiblity of torrential rains or blizzards, I was talking about the height of the great bombardment, that could be sampled very deep in the section, not the very tail end, that has perhaps been sampled at Meridiani at the top. (Because layered rocks are always deposited from the bottom up.) By then I think Mars had largely reached its present cold, dry state, as mentioned previously.

On Earth, low areas can easily gain great elevation, owing to plate tectonic processes, but on Mars, I doubt it, unless you intruded a huge body of molten rock underneath, and rafted things up. There is little evidence of such a process. You can erode off the top, to a certain extent, and fill in low spots, and build extremely tall basaltic volcanoes, which need to be gravitationally compensated via extemely broad and gentle warping elsewhere, and accumulate polar ice caps, but that's about it offhand (I'm probably leaving something important out, although I'm including glaciers and outflow channels in the above).

Capillary action of migrating salts combined with dune accretion on sticky surfaces might indeed eventually form and preserve sandstones - a thoughtful suggestion - but they would not contain spherules. It was the spherules that first made us think of impact. Also, in terms of "incomplete water record" I would instead argue at this point that we have "no water record" at all in terms of liquid water - and I have spent much of my professional life looking for indications of the passage of liquid water in mineral deposits. I agree that exposures deep in Victoria may change that, but I'm not optimistic.

The critical way that the MER team changed their story between 2004 and 2005, apparently in response to our impact hypothesis, was to admit that the highly improbable (in terms of evaporation) mixture of salts must have been transported from somewhere else. Why did one of them publicly deny that change in 2006? I don't know. Perhaps because the putative "playa" had by then logically lost its home at huge Meridiani, unless the depths of Victoria reveal some highly distinctive lake beds, not seen in any ejecta. In terms of what they originally considered, I have been led to believe, possibly erroneously, that they considered only volcanic surge, not impact surge, as a possibility for the cross-bedding and spherules (in part because a person they consulted was my co-author Ken Wohletz). I freely admit that I am trying to poke holes in (or "belittling") their arguments - that's the only way science can advance. Please feel free to belittle mine - that's what I'm here for. I won't take it personally. (And even if I did, what could I do about it except get banned from this forum?)

I fully agree with you that today's Mars is dynamic and geologically active. That's part of its excitement. My personal prejudice, which I have certainly made no secret of biggrin.gif , is that most of the really "heavy lifting" got done billions of years ago by impacts. Most Mars scientists agree that impacts and wind are the dominant processes affecting the entire surface today, and seem to have been for a very long time. And impacts may provide the real "bursts" to which you refer in terms of active processes.

Thanks for helping me clarify some of my ideas. I much appreciate it.

--HDP Don

Posted by: hendric Jul 6 2007, 05:34 AM

Dburt,
I've had a few nagging questions on the impact surge hypothesis:

1. How can an impact surge explain berry multiples where the berries are not the same size? See, eg

http://marsrovers.nasa.gov/gallery/press/opportunity/20040312a.html

My thoughts are that if the berries meld together on the ground, then they should have all fallen at about the same time, and therefore should be the same size.

If the berries melded together in the air, they should also be the same size, for the above reason, except moreso.

Also, the chance of them forming a straight line is very slim by impacting one another in a cloud or on the ground.

2. The ground is currently covered in blueberries, at least around Eagle and Endurance. If the berries were caused by multiple impact surges, where is the record of the previous lag deposits? IE, there should be occasional layers of berries in the outcrop, corresponding with time between impacts where erosion extracted them from the deposits, yet we don't see any.

Posted by: dvandorn Jul 6 2007, 06:04 AM

QUOTE (dburt @ Jul 6 2007, 12:13 AM) *
Regarding the apparent hardness of the Meridiani rocks, remember that Mars gravity is weak, the Meridani cliffs are visibly crumbling, and the wind appears to have carved them like a knife. So they can't be all that hard.

Yes, but... the rocks at Gusev are all dense basalts (as can be observed empirically and also inferred from dozens of different sensor measurements), and *they* have also been carved by the wind, like a knife through butter.

Doesn't matter how hard the rocks are or how thin the air is -- if you blow on rocks with wind for long enough, you get aeolian erosion. Doesn't matter how dense or light the rocks are.

-the other Doug

Posted by: MarsIsImportant Jul 6 2007, 03:16 PM

Good point "the other Doug".

I'd also extend this idea to point out that the cliffs at Victoria are still there after billions of years. The mere fact that they are still there is a good indication that these layers are hard indeed.

The point that the Professor made about not being able to tell the hardness from the RAT tool is not accurate. Yes, you can determine the relative hardness from the rate of the RAT digging into the rock (at least to within a certain parameter, not exact but we don't need exact--just relative). And the MER team can determine a relative standard of comparison from Gusev. Spirit has found a variety of hard and soft rocks. The soft rocks at Gusev may correspond well with what the Professor has talked about; but the layered rocks at Meridiani are much harder than those soft rocks at Gusev.

As for the weight of the rover on Mars being a lot less because of less gravity, that point is well taken. But I had accounted for the less gravity already. The rover is still relatively heavy and should have made some kind of mark on the underlying layered deposits, if they are as soft as he suggests. Given the uncertainty factor, I pointed out the RAT tool evidence as confirmation. But if that was not enough, then the view of Victoria crater should be. Either the soft rocks are much younger and Victoria is NOT billions of years old; or the relatively HARD rocks are old and Victoria is billions of years old. You cannot have it both ways. If the layered rocks were soft, then billions of years should have eroded the crater to look more like Erebus. The possibility that the rocks are soft and Victoria is relatively young has drastic implications that destroy many of the assumptions that the Professor holds dearly. For that matter, it would also destroy many of the assumptions that the MER team has operated with too. My point is that I don't think any of us "want to go there".

Posted by: don Jul 6 2007, 03:55 PM

dburt - A repentant Prof Burt !! A tear just rolled down my cheek. Where was this quality when you were grading Igneous Petrology papers back in our youth ? biggrin.gif

I agree with your statement about personal bias, you’ll see what your comfort level allows you to see. For me the bias is groundwater/aquifer geochemistry. So from a 50,000 foot view the MER team account of a paleo-regional groundwater system at meridiani with an extended diagenetic history has some merit. Obviously the story gets complicated as the resolution increases but that may be a hindrance at this time - we see only the tree in the proverbial forest in terms of rock geochemsitry. Granted, the devil is in the detail, but given our inexperience with >3 byr old terrain, I suspect we have overlooked a detail or two.

If water was retained within the sediments for even a fraction of the rocks proposed age ( >3 byrs) the potential for diagentic alteration is endless - interaction or mixing of different aquifers, dewatering of the aquifer, aquifer recharge with different water type, volcanic gas flux, impact, surficial water infiltration, etc. In other words, throw out those mass balance models for now and you’ll sleep better at night. Finally, the geographic coverage of meridiani is great but certainly in line with the areal extent of the High Plains aquifer that underlies parts of eight western U.S. states. Size alone should not an obstacle for an exhumed aquifer at meridiani.

Posted by: Kye Goodwin Jul 6 2007, 04:03 PM

Details, details. A major reason why I have become convinced that the impact-surge hypothesis is realistic is that the rough fit with Mars is so excellent. Huge impact craters are the single most prominent feature of the Southern Highlands from space. They are clearly ancient and yet have been preserved, a fact that makes it very likely that the inter-crater plains are still covered by their ejecta. Land in the highlands and you are very likely to see ejecta. Outside the volcanic areas impact ejecta should be the commonest sort of material. Mars craters over a certain size (roughly 5 km diameter) often produce a continuous ejecta blanket that suggests fluidized emplacement, and the indications of fluidization generally increase with crater diameter as does the trend to produce double and multiple layers of ejecta.

The large-scale regularly-layered landscapes visible from orbit have been especially difficult to understand. Really there has never before been an explantion that seemed better than barely possible. The brine-splat authors have made this connection, but only in the most general way. I am glad to read that Doctor Burt is not shy about conjecturing and I am hoping that he will be willing to write something more for us about how impact-surge might explain the widespread large-scale layers.

Posted by: MarsIsImportant Jul 6 2007, 04:40 PM

Well, since conjecturing is in play. Another possibility is that the Late Heavy Bombardment is not the only evident heavy bombardment that occurred. Just conjecturing and brain storming but (and I have my doubts about this) maybe Mars records multiple and even later bombardments which we have not accounted for yet. Perhaps our solar system was relatively recently much more like Tau Ceti is now. Then the question becomes what event changed things here. It's a huge "can of worms" that crosses many disciplines.

Perhaps instead, many craters were secondary and tertiary products from a late planetary type impact. Or possibly the large Volcanoes on Mars created such large explosions that many projectiles created crater impacts all over the planet. If that is the case, then terrain that seems very old may not be nearly as old as it first appears. Again, 'a monkey wrench' is thrown into our original thought processes. And again, I have my doubts about these issues I'm bring up in this post.

Posted by: dvandorn Jul 6 2007, 05:55 PM

The problem with positing a series of heavy bombardments, dating up until fairly recent times, is that we don't see a record for such a bombardment on Earth or Luna. While it is possible, I suppose, for bombardments to be set into motion that only affect a certain portion of the local neighborhood, I'd imagine that a heavy bombardment which would affect Mars would also affect Earth/Luna, and probably Venus and Mercury as well.

There have indeed been models put forth to explain the LHB in terms of migration of major outer planets -- the one I can remember best suggests that Jupiter originally formed farther from the Sun than Saturn did, and that as it migrated closer to our star it tossed Saturn further out and disrupted whatever rocky body (or bodies) occupied the orbital neighborhood that now lies between Mars and Jupiter. This disruption caused a great deal of the mass located in what is now the Asteroid Belt to fall towards the inner system... and smash into any inner rocky planet or moon that stood in its path.

Yes, there could have been other less major disruptions that could have caused a lot of the debris in the current Asteroid Belt to have meandered in towards Mars' orbit. But even without detailed mathematical calculations, my gut feeling is that anything that would have caused a major bombardment on Mars should also extend itself in towards the rest of the inner system. And the problem with that is that the most recent of Luna's large craters seems to be on the order of 100 million years, and those are very scarce. The shoulder-to-shoulder large crater structures on Luna are all of an age, and that age is somewhere around 3by ago.

Remember, the LHB resurfaced much of Luna, and from the looks of it, resurfaced much of Mars, as well. The same thing happened on Earth, of course, but Terra has effectively resurfaced itself many times since then and the crater remnants of the LHB are almost all gone by now.

I just don't see any way for a major disruption to pull enough mass in towards Mars to create a major bombardment and yet not toss enough of that mass in to the inner system to leave a record on Luna. I guess I'd say it's possible but extremely unlikely.

-the other Doug

Posted by: MarsIsImportant Jul 6 2007, 06:18 PM

That's why a more local event particular to Mars is more probable, such as one huge planetary impact. Debris could have been thrown into orbit and it fell to the surface much later. Perhaps the moons of Mars are remnants of such an impact.

One more big 'monkey wrench' that is not conjecture has been reported in the last couple of days. Mars Express has found a lot of clays on Mars that could Not form on the surface with much CO2 in the atmosphere. That highly suggests that the ancient Mars atmosphere was far different than anything we so far assumed.

http://space.newscientist.com/article/dn12202-more-doubt-cast-on-warm-wet-early-mars.html

The headline of the article makes an assumption. And that assumption is one of many possibilities. First of all, these clays were made. And they must have been made in the presence of water without CO2. So some major event or events changed things substancially on Mars.

Posted by: dburt Jul 6 2007, 06:45 PM

QUOTE (centsworth_II @ Jul 4 2007, 07:57 PM) *
HDP Don,
Tell me again why you're having trouble making friends
and influencing people in the scientific establishment? biggrin.gif


Hey, along with a childlike curiosity about the wonders of the universe goes a childlike tendency to mock any authority that is perceived as foolish or pretentious. Call it a dangerous occupational hazard of scientists. In any case, feel free to mock my ideas all you want. smile.gif

--HDP Don

Posted by: ElkGroveDan Jul 6 2007, 07:06 PM

QUOTE (dburt @ Jul 6 2007, 10:45 AM) *
Hey, along with a childlike curiosity about the wonders of the universe goes a childlike tendency to mock any authority that is perceived as foolish or pretentious.


Remember they laughed at Galileo, they laughed at Albert Einstein and they laughed at Bob Hope.

Posted by: dburt Jul 6 2007, 07:17 PM

QUOTE (hendric @ Jul 5 2007, 10:34 PM) *
Dburt,
1. How can an impact surge explain berry multiples where the berries are not the same size?

My thoughts are that if the berries meld together on the ground, then they should have all fallen at about the same time, and therefore should be the same size.

If the berries melded together in the air, they should also be the same size, for the above reason, except moreso.

Also, the chance of them forming a straight line is very slim by impacting one another in a cloud or on the ground.

2. The ground is currently covered in blueberries, at least around Eagle and Endurance. If the berries were caused by multiple impact surges, where is the record of the previous lag deposits? IE, there should be occasional layers of berries in the outcrop, corresponding with time between impacts where erosion extracted them from the deposits, yet we don't see any.


Good questions. 1) Growth in a turbulent cloud does not mean they all have to be the same size - they just should not exceed a certain size (more mass than the cloud can support). If three spherules happen to stick together during growth, and are spinning about a common center of gravity, then they should tend to line up, and also be smaller than the largest spherules (so that their combined mass does not exceed what the cloud can support). That seems to be the case here. (BTW, can you imagine how tired I am of seeing that one triplet photo as "typical" of all the millions of spherules out there?) Actual concretions growing in rocks tend to merge together in nodular masses at random orientations, semi-random sizes, semi-random shapes, and random numbers of berries, up to dozens or many hundreds. I am still waiting to see such a feature (that is, wherever the spherules are densely packed together, they are still entirely separate entities). As you mention, another way to line berries up might be after deposition, if they land lined up along a pre-existing crack, and then develop salt encrustations that "glue" them together. No evidence of that here, though.

2) I have no idea at this point how many impact surges might be represented in rock exposures at Meridiani, or what the time interval was between impacts. If there were a Meridiani-like lag deposit on the ground when the second impact surge arrived, it would almost certainly be scoured away and incorporated into the new surge cloud. In that manner you could spread spherules across a much wider area that that originally covered, and that may have happened across parts of Meridiani (just look at all the spherules spread around by Victoria Crater).

Thanks for the great questions. Keep'm coming!

--HPD Don

Posted by: dburt Jul 6 2007, 07:56 PM

QUOTE (MarsIsImportant @ Jul 6 2007, 08:16 AM) *
Good point "the other Doug".

I'd also extend this idea to point out that the cliffs at Victoria are still there after billions of years. The mere fact that they are still there is a good indication that these layers are hard indeed.

The point that the Professor made about not being able to tell the hardness from the RAT tool is not accurate. Yes, you can determine the relative hardness from the rate of the RAT digging into the rock (at least to within a certain parameter, not exact but we don't need exact--just relative). And the MER team can determine a relative standard of comparison from Gusev. Spirit has found a variety of hard and soft rocks. The soft rocks at Gusev may correspond well with what the Professor has talked about; but the layered rocks at Meridiani are much harder than those soft rocks at Gusev.

As for the weight of the rover on Mars being a lot less because of less gravity, that point is well taken. But I had accounted for the less gravity already. The rover is still relatively heavy and should have made some kind of mark on the underlying layered deposits, if they are as soft as he suggests. Given the uncertainty factor, I pointed out the RAT tool evidence as confirmation. But if that was not enough, then the view of Victoria crater should be. Either the soft rocks are much younger and Victoria is NOT billions of years old; or the relatively HARD rocks are old and Victoria is billions of years old. You cannot have it both ways. If the layered rocks were soft, then billions of years should have eroded the crater to look more like Erebus. The possibility that the rocks are soft and Victoria is relatively young has drastic implications that destroy many of the assumptions that the Professor holds dearly. For that matter, it would also destroy many of the assumptions that the MER team has operated with too. My point is that I don't think any of us "want to go there".


MarsIsImportant - What can I say? I've never hammered on a Mars rock. The terrestrial surge deposits I've examined vary considerably in their hardness, but you generally need a rock hammer to break them. Nevertheless, they're softer than basalt (many are kind of like adobe). If the wind has only eroded 10 meters or so of Meridiani outcrops over 3.8 billion years, that probably has more to say about the ineffectiveness of wind erosion on near-vacuum Mars than it does about the intrinsic hardness of the rocks. Also, the impact surge hypothesis, unlike the vanished playa lake hypothesis, does not require Mars to be any different than it is today, so the topmost surge deposits could be considerably younger than 3.8 billion years, and still look the way they do. At Gusev, the various larger basalt pieces on top could well be impact ejecta of almost any age. Without any time calibration, further speculation trying to relate hardness to amount of erosion would be pointless, IMHO. Thanks for the discussion, though.

--HDP Don

Posted by: MarsIsImportant Jul 6 2007, 08:13 PM

QUOTE (dburt @ Jul 6 2007, 02:17 PM) *
2) I have no idea at this point how many impact surges might be represented in rock exposures at Meridiani, or what the time interval was between impacts. If there were a Meridiani-like lag deposit on the ground when the second impact surge arrived, it would almost certainly be scoured away and incorporated into the new surge cloud. In that manner you could spread spherules across a much wider area that that originally covered, and that may have happened across parts of Meridiani (just look at all the spherules spread around by Victoria Crater).


I appreciate your honestly. You don't know how many impact surges were needed to create Meridiani.

If the new impact surge scoured the ground and incorporated the previous deposits, then many layers at Meridiani would be missing. Also, the layers themselves should be a lot thicker than appear.

Instead, Meridiani shows thousands upon thousands of very thin layers. In my mind that suggests more like seasonal dust deposits. Doesn't it make more sense that the dust storms that we see every two years on Mars deposits the thin layers? When water was available, then the dust was cemented. That process stopped a long time ago; but the seasonal dust storms continue. If this layering process occurred over a very long time, then it is possible that surge clouds of some sort might have created the berries--I don't know. But I still think that the groundwater significantly altered these rocks.

Regardless, your hypothesis does not account for the vugs found at Eagle crater. You asked where were the crystals. But they found the cavities where crystals once were. Then, the crystals later dissolved again in solution and the salts carried away by some presumed liquid. It's possible that all the evidence is really from groundwater or brine of some sort at various times in the distant past. Perhaps aeolian processes excavated large parts of Meridiani. But that would suggest Victoria would need to be more recent of an event (I doubt it).

When we have a known process for deposition--the dust storms--why would we need another one, especially when the known one would create the fine thin layers that we see? I don't understand why we need another process when lithification of these layers through groundwater is perfectly plausable.

You point out the concretions are not what they seem to be. Ok. They might have been formed by Volcanic surges tool Couldn't they have? You stated yourself that we have no good examples of impact surges. Even you are using Volcanic surges as a standard. If memory serves me well, even the MER team has been open to the possibility of some sort of volcanic activity nearby. Perhaps the berries are not concretions but a result of periodic volcanic activity. But I don't think the dust layers are a result of the surge mechanism you propose. A series of surges would simply not make such fine layers.

Posted by: MarsIsImportant Jul 6 2007, 08:20 PM

QUOTE (dburt @ Jul 6 2007, 02:56 PM) *
MarsIsImportant - What can I say? I've never hammered on a Mars rock. The terrestrial surge deposits I've examined vary considerably in their hardness, but you generally need a rock hammer to break them. Nevertheless, they're softer than basalt (many are kind of like adobe). If the wind has only eroded 10 meters or so of Meridiani outcrops over 3.8 billion years, that probably has more to say about the ineffectiveness of wind erosion on near-vacuum Mars than it does about the intrinsic hardness of the rocks. Also, the impact surge hypothesis, unlike the vanished playa lake hypothesis, does not require Mars to be any different than it is today, so the topmost surge deposits could be considerably younger than 3.8 billion years, and still look the way they do. At Gusev, the various larger basalt pieces on top could well be impact ejecta of almost any age. Without any time calibration, further speculation trying to relate hardness to amount of erosion would be pointless, IMHO. Thanks for the discussion, though.

--HDP Don


You haven't hammered on the rocks at Meridiani; but NASA has. You are forgetting that parts of the space craft slammed into the Meridiani surface and the heat shield was examine by opportunity. The impact barely made a dent into the surface. We can easily calculate all the forces involved. In does not take much to realize that the surface rock layers are very hard. They must have been cemented together by water over a long period of time.

Posted by: dburt Jul 6 2007, 08:25 PM

QUOTE (don @ Jul 6 2007, 08:55 AM) *
dburt - A repentant Prof Burt !! A tear just rolled down my cheek. Where was this quality when you were grading Igneous Petrology papers back in our youth ? biggrin.gif

I agree with your statement about personal bias, you’ll see what your comfort level allows you to see. For me the bias is groundwater/aquifer geochemistry. So from a 50,000 foot view the MER team account of a paleo-regional groundwater system at meridiani with an extended diagenetic history has some merit. Obviously the story gets complicated as the resolution increases but that may be a hindrance at this time - we see only the tree in the proverbial forest in terms of rock geochemsitry. Granted, the devil is in the detail, but given our inexperience with >3 byr old terrain, I suspect we have overlooked a detail or two.

If water was retained within the sediments for even a fraction of the rocks proposed age ( >3 byrs) the potential for diagentic alteration is endless - interaction or mixing of different aquifers, dewatering of the aquifer, aquifer recharge with different water type, volcanic gas flux, impact, surficial water infiltration, etc. In other words, throw out those mass balance models for now and you’ll sleep better at night. Finally, the geographic coverage of meridiani is great but certainly in line with the areal extent of the High Plains aquifer that underlies parts of eight western U.S. states. Size alone should not an obstacle for an exhumed aquifer at meridiani.


Other Don - That's all well and good, but many things are theoretically possible (including little green men, perhaps). Just show me the evidence, please. More to the point, are there any features at Meridiani (or Gusev, or any of those many other salty layered deposits all around the Mars highlands) that CAN'T be accounted for by the impact surge hypothesis?

Thanks,

--HDP Don

Posted by: nprev Jul 6 2007, 08:47 PM

Forgive me if this has been asked & answered earlier, DB, but how fast would blueberries be expected to form in your scenario? I have a hard time imagining that the 'splat' conditions would persist long enough to let them form via accretional processes, and frankly they just don't look like tektites or another form of melt product to me because of their symmetry and those weird little bumps some of them have (which seem to be more common on berries in protected locations; maybe they get weathered off of the surface berries due to rolling around by the wind?) The spectrum of sizes at different locations is odd as well, and seems to argue for a more gradual formation process. Has there been any sort of detailed morphological analysis of them?

QUOTE (ElkGroveDan @ Jul 6 2007, 12:06 PM) *
Remember they laughed at Galileo, they laughed at Albert Einstein and they laughed at Bob Hope.


Yeah, but for truly enduring comedy you just can't beat Hoaxland... wink.gif...how the hell does he get out of those straightjackets so fast?

Posted by: dburt Jul 6 2007, 08:51 PM

QUOTE (MarsIsImportant @ Jul 6 2007, 01:20 PM) *
You haven't hammered on the rocks at Meridiani; but NASA has. You are forgetting that parts of the space craft slammed into the Meridiani surface and the heat shield was examine by opportunity. The impact barely made a dent into the surface. We can easily calculate all the forces involved. In does not take much to realize that the surface rock layers are very hard. They must have been cemented together by water over a long period of time.


Sorry, I have trouble quantifying "very hard" and rocks generally don't "dent" unless they're squishy mud or hit at hypervelocity, forming an impact crater. Also, if the grains were cemented together by water over a very long time, were there any cements available other than the abundant sulfate salts that we see? If not, how would that salt cement make the rocks harder than the surge hypothesis would account for? In fact, why weren't the basaltic sand grains simply altered to "soft gunk" (crystalline clays) if they were soaked for so long in liquid water? None of these problems seem to occur with "Boom!" (at least as I see it in in my admittedly biased way). Thanks for the good discussion.

--HDP Don

Posted by: dburt Jul 6 2007, 09:21 PM

QUOTE (MarsIsImportant @ Jul 6 2007, 01:13 PM) *
I appreciate your honestly. You don't know how many impact surges were needed to create Meridiani.

If the new impact surge scoured the ground and incorporated the previous deposits, then many layers at Meridiani would be missing. Also, the layers themselves should be a lot thicker than appear.

Instead, Meridiani shows thousands upon thousands of very thin layers. In my mind that suggests more like seasonal dust deposits. Doesn't it make more sense that the dust storms that we see every two years on Mars deposits the thin layers? When water was available, then the dust was cemented. That process stopped a long time ago; but the seasonal dust storms continue. If this layering process occurred over a very long time, then it is possible that surge clouds of some sort might have created the berries--I don't know. But I still think that the groundwater significantly altered these rocks.

Regardless, your hypothesis does not account for the vugs found at Eagle crater. You asked where were the crystals. But they found the cavities where crystals once were. Then, the crystals later dissolved again in solution and the salts carried away by some presumed liquid. It's possible that all the evidence is really from groundwater or brine of some sort at various times in the distant past. Perhaps aeolian processes excavated large parts of Meridiani. But that would suggest Victoria would need to be more recent of an event (I doubt it).

When we have a known process for deposition--the dust storms--why would we need another one, especially when the known one would create the fine thin layers that we see? I don't understand why we need another process when lithification of these layers through groundwater is perfectly plausable.

You point out the concretions are not what they seem to be. Ok. They might have been formed by Volcanic surges tool Couldn't they have? You stated yourself that we have no good examples of impact surges. Even you are using Volcanic surges as a standard. If memory serves me well, even the MER team has been open to the possibility of some sort of volcanic activity nearby. Perhaps the berries are not concretions but a result of periodic volcanic activity. But I don't think the dust layers are a result of the surge mechanism you propose. A series of surges would simply not make such fine layers.


MarsIsImportant - I'd really prefer it if you could give me one question per post, rather than this stream of consciousness type of questioning. Much easier for me to try to answer, and much easier for people to read. Thanks.

Regarding missing and thin layers - the exposures in Endeavor are very limited, and haven't been matched yet with exposures in Victoria. Besides, the scouring in a given area would probably be fairly uniform. Each cross-bed represents a scouring episode, but probably just owing to turbulence in a single surge cloud. Surges have no problem building up numerous fine layers in a single episode, as covered in previous posts. Also, the Meridiani material seems to be mainly sand, not dust.

Regarding the crystal-shaped vugs - the impact surge hypothesis accounts for them just fine, if they represent a former chloride mineral. Chlorides are much more soluble and also subject to frost leaching (owing to much greater freezing point depression) than the surrounding sulfates. Minor post-depositional drainage or frost leaching also accounts for why the chloride content seems to increase with depth. This was covered in our original Nature paper from 2005 (attached to a previous post).

Regarding possible volcanism - as covered in a recent post, the MER team early on dismissed volcanism as a causative agent for the cross-bedding and berries, and we have never disputed that finding (although others have).

Remember, not so many different questions per post, please. Thanks for them though.

--HDP Don

Posted by: MarsIsImportant Jul 6 2007, 09:22 PM

Ok. Hardness doesn't matter. I only keyed on that issue because you stated that the layered rocks at Meridiani were soft. So it is Not a problem for either theory or hypothesis (whatever you want to call them).

I still have a big problem with the thickness of the layers. The thin layers observed, support the MER team's hypothesis.

Posted by: dburt Jul 6 2007, 09:48 PM

QUOTE (nprev @ Jul 6 2007, 01:47 PM) *
Forgive me if this has been asked & answered earlier, DB, but how fast would blueberries be expected to form in your scenario? I have a hard time imagining that the 'splat' conditions would persist long enough to let them form via accretional processes, and frankly they just don't look like tektites or another form of melt product to me because of their symmetry and those weird little bumps some of them have (which seem to be more common on berries in protected locations; maybe they get weathered off of the surface berries due to rolling around by the wind?) The spectrum of sizes at different locations is odd as well, and seems to argue for a more gradual formation process. Has there been any sort of detailed morphological analysis of them?

Nprev - Good question, but I can't answer it. I would expect a time of something from minutes to hours, depending on the size of the impactor and where in the cloud they condensed. If they grew in a mushroom-shaped cloud directly over the impact site, that might give them longer and allow them to grow larger, but then a second nearby impact might be needed to distribute them over wide areas in a surge cloud. On the other hand, the mushroom cloud itself might eventually gravitationally collapse as it condensed and cooled in the very thin atmosphere (like a downburst in a thunderhead cloud), and form a surge deposit on top of an earlier blast surge. Pure speculation at this point, I'm afraid.

Rolling along on the ground owing to the force of the surge cloud certainly seems possible, as mentioned in a previous post. Rolling owing to the wind, not observed. For me the only key observation about the spectrum of sizes is the strict size limitation at about 5 mm. Condensation-related impact spherules are entirely different from the shaped splash droplets called tektites, as covered in a previous post. I don't offhand know of a detailed morphological analysis, but would be surprised if one had not been done, perhaps by someone in another forum.

Keep'm coming, but I may not get to them for awhile.

--Don

Posted by: dburt Jul 6 2007, 09:50 PM

QUOTE (MarsIsImportant @ Jul 6 2007, 02:22 PM) *
I still have a big problem with the thickness of the layers. The thin layers observed, support the MER team's hypothesis.


Howso?

--HDP Don

P.S.: Sorry, I'll take pity on you - I think the thinness of the layers has already been discussed in numerous previous posts, as not being particularly diagnostic of either of the suggested processes. I just wanted to see if I could actually make a one-word reply, for once smile.gif I dood it! HDP Don

Posted by: MarsIsImportant Jul 6 2007, 10:19 PM

The MER team ruled out Volcanism as a causative agent for the cross-bedding and the berries. The wording is important. This does not rule out the possibility of volcanism providing the heat necessary to have the liquid water given their hyposthesis.

One of the problems you seem to have with the MER team hyposthesis is that Mars has been a cold dry place for billions of years. Well, we now know that there was plenty of H2O around. But was it in the correct state? The current atmosphere suggests "No". But now we know that the atmosphere must have changed drastically over the billions of years, because the massive amounts of clays found by Mars Express cannot be formed with CO2 predominant in the atmosphere. The ancient atmosphere of Mars was not of CO2. As far as we know, the atmosphere could have been a lot thicker and supported liquid water on the surface at one time. We cannot be sure one way or another yet. But if we believe the MER team, the answer is highly suggested to be "Yes". Liquid water on or near the surface is the basis for their hypothesis.

From the beginning, I have not ruled out the possibility of impact surge contributing to the geology of Mars. I just don't believe it was predominant like you suggest at Meridiani. I don't know how you could convince me otherwise.

Your best argument seems to deal with the berries themselves. But their differing shapes over most of the terrain observed by Opportunity seems to be a problem (frankly, for both hypotheis). They have been completely round until we approached Victoria...yet not exactly round near Victoria. Why? How does the shape or change in shape fit with your impact surge hypothesis?

Posted by: MarsIsImportant Jul 6 2007, 10:21 PM

QUOTE (dburt @ Jul 6 2007, 04:50 PM) *
Howso?

--HDP Don


...because of the seasonal dust storms creating the mechnism for such layers. I already explained that.

Posted by: dvandorn Jul 6 2007, 10:29 PM

Just one last comment on the relative softness of the rocks on Mars:

There is one other measure of the hardness of the rocks that hasn't yet been mentioned. The RAT on Spirit wore out considerably faster than has the RAT on Opportunity. The RAT cutting edges were identical on MER-A and MER-B, so there is a quantifiable and measurable amount by which the rocks at Gusev are harder than the rocks at Meridiani. (I believe some estimate of Mohs scale was made for the various rocks that have been RATted, based on the amount of electrical power required to make the observed cuts. I don't know where I read that, though, and so I can only offer it as a piece of potential apocrypha.)

My own take on it is that the Meridiani rocks are probably pretty friable when you apply pressure cross-layer. But the way those layers have cemented give the rocks a fairly decent load-bearing strength when you apply pressure along a layer's plane. In other words, it's like plywood -- you can easily crumble off the edges, but sit on a slab of it and it won't tend so much to crack and crumble. Or, to sound like I know more than I do, the material's axis of greatest strength is planar and alined with the layers... smile.gif

The very few surviving blocks of ejecta made of this material show preferential erosion cross-layer, as well. An ejecta block with a flat, contiguous layer for much of an exposed face appears to erode selectively along its non-planar faces. This would tend to support that the material is stronger (i.e., more erosion-resistant) when force is applied perpendicular to the plane. However, the rather noticeable lack of extant ejecta blocks from this material, as well as the "ground-down" condition of what now look like flat pavement slabs at various places in this unit, also speaks to material that is soft and relatively easily eroded.

-the other Doug

Posted by: dburt Jul 6 2007, 10:34 PM

QUOTE (MarsIsImportant @ Jul 6 2007, 03:21 PM) *
...because of the seasonal dust storms creating the mechnism for such layers. I already explained that.

But the layers are not dusty, but sandy, as I explained in my reply.

--HDP Don

Posted by: dburt Jul 6 2007, 10:59 PM

QUOTE (MarsIsImportant @ Jul 6 2007, 03:19 PM) *
The MER team ruled out Volcanism as a causative agent for the cross-bedding and the berries. The wording is important. This does not rule out the possibility of volcanism providing the heat necessary to have the liquid water given their hyposthesis.

One of the problems you seem to have with the MER team hyposthesis is that Mars has been a cold dry place for billions of years. Well, we now know that there was plenty of H2O around. But was it in the correct state? The current atmosphere suggests "No". But now we know that the atmosphere must have changed drastically over the billions of years, because the massive amounts of clays found by Mars Express cannot be formed with CO2 predominant in the atmosphere. The ancient atmosphere of Mars was not of CO2. As far as we know, the atmosphere could have been a lot thicker and supported liquid water on the surface at one time. We cannot be sure one way or another yet. But if we believe the MER team, the answer is highly suggested to be "Yes". Liquid water on or near the surface is the basis for their hypothesis.

From the beginning, I have not ruled out the possibility of impact surge contributing to the geology of Mars. I just don't believe it was predominant like you suggest at Meridiani. I don't know how you could convince me otherwise.

Your best argument seems to deal with the berries themselves. But their differing shapes over most of the terrain observed by Opportunity seems to be a problem (frankly, for both hypotheis). They have been completely round until we approached Victoria...yet not exactly round near Victoria. Why? How does the shape or change in shape fit with your impact surge hypothesis?


MarsIsImportant - Regarding volcanic heat, one of the reasons the MER team rejected volcanism was that there were no signs whatever of any volcanic phenomena anywhere in the vicinity. No volcanism = no volcanic heat for melting. Also, unlike on Earth, volcanism on Mars does not ever appeared to have moved around, owing to the lack of plate tectonics. The main reason why the volcanoes are so big is that volcanism has always stayed in the same place.

Regarding crystalline clays - they seem to occur only in the very oldest, most heavily cratered areas of Mars, and are rare there. They probably have nothing to do with Meridiani itself, which appears to be much younger. They could reflect water melting or condensation that occurred at the height of the late heavy bombardment, or volcanic heating, or a different climate back then. No one knows.

I'm not trying to convince you of anything about Meridiani - just trying to open your eyes to all the possibilities, so that you can make up your own mind, based on the evidence as you understand it. And the berries to me are still pretty round near Victoria, although some of them may have been eroded a bit by the wind (everything else was, that's for sure). They also could have been affected by the Victoria-forming impact itself, during the excavation process. Thanks for the discussion.

--HDP Don

Posted by: dburt Jul 6 2007, 11:06 PM

QUOTE (dvandorn @ Jul 6 2007, 03:29 PM) *
Just one last comment on the relative softness of the rocks on Mars:

...deleted... However, the rather noticeable lack of extant ejecta blocks from this material, as well as the "ground-down" condition of what now look like flat pavement slabs at various places in this unit, also speaks to material that is soft and relatively easily eroded.

-the other Doug


Thanks for answering that far better than I did. smile.gif

--HDP Don

Posted by: tdemko Jul 7 2007, 03:33 AM

As some of you know, I don't have nearly the time to devote to thoughtful posts as I used to...but be that as it may, I see in my review of the recent flurry of posts that my name has been called upon for some sedimentological input:

- single grain (or a few grain) layer lamination: the most common occurrences of these in the terrestrial stratigraphic record are due to three processes: 1) Stokes settling, 2) upper stage/critical flow regime streaming, and 3) ballistic/translatent ripple migration. 1) and 2) are subaqueous processes and 3) is aeolian. Stokes settling is simple gravitational fall-out of material suspended in a fluid, with particles sorted by their velocity (generally grain size and density, although drag and grain Reynolds number also are important with non-spherical grains). The results are things like varves, laminated lake clays, and deep-sea oozes, with some amount of grading apparent. Upper stage/critical flow regime streaming occurs when the shear stress at the bed is such that bedforms such as ripples and dunes can not form, but is not exceeding a point at which antidunes or chutes and pools form. http://faculty.gg.uwyo.edu/heller/SedMovs/mcbridelam.htm, and as velocity wanes, a plane, flat lamination forms before dunes and ripples. There may be low relief (1-2 grains thick) stripes that form down-current due to rollers and stretched-out vortices near the boundary layer. These are expressed as parting lineation in indurated sandstones. These features are common in river, tide, and beach (swashface/foreshore) sandstones, the Tb part of Bouma successions (turbidites), and pyroclastic flows and base-surge deposits. The migration of ballistic or translatent ripples in aeolian regimes produces pinstripe lamination, with alternating finer and coarser grained layers only a grain or two thick. Foreset laminae are generally not present in these types of ripples, and cross lamination is rare in most aeolian deposits. Cross-bedding, on the other hand, is almost always present.

- formation of martian sandstones: siliciclastic sand, of course, forms from breaking up big rocks into smaller ones. Because of the upper size limit of sand (2 mm), most grains in sandstones are either mono-mineralic or are made up of 2 or 3 crystals of different minerals still stuck together by other means (igneous or metamorphic crystallization or sedimentary cementation). Chemical and physical weathering processes on earth can be quite efficient in breaking rocks down to sand and silt size, and the abundance of sandstones and siltstones is related to the distribution of crystal/grain sizes in the parent material. Induration can result from geochemical processes related to the original constituents (pressure solution, dissolution/reprecipitiation, etc.) or post-depositional additions (cement, neomorphic clays, etc.). I guess for me, the larger questions of sandstone formation on Mars are the mechanisms under which sorting to sand-sized material (to a deposit that could be preserved as a sandstone) takes place, and how deep burial (sedimentary basin formation) can occur without an obvious plate tectonic engine driving crustal deformation.

- scour surfaces in aeolian deposits (or their absence): scour surfaces are ubiquitous in aeolian deposits. Stokes surfaces, or supersurfaces, form by regional deflation to a water table. Brookfield surfaces form a hierarchy of bounding migration surfaces of dunes, draas, and larger bedform families. Changes in wind speed, direction, or sand supply can result in regional deflation, and local blow-outs form down-wind of and between dunes at zones of air flow reattachment or impingement.

Don Burt's catastrophist/non-uniformitarian ideas have also made me start to think again about the dynamic nature of Mars climate and paleoclimate. I keep having this nagging suspicion that we have yet to completely comprehend the full impact of Mars precession and obliquity cycles and how they control global volatile distribution (and state). This, plus our generally impact-poor view of surficial processes, makes us ill-prepared to, as Bill Shakespeare once said "figure the nature of the times deceased" on Mars.

Posted by: MarsIsImportant Jul 7 2007, 04:13 AM

QUOTE (dburt @ Jul 6 2007, 05:34 PM) *
But the layers are not dusty, but sandy, as I explained in my reply.

--HDP Don


The sand on Mars is like fine dust on Earth. Looking with the Micro-Imager, the dust looks sandy. The really fine dust in the high atmosphere is not what I was necessarily referring to. You can see the tracks of the rover dramatically change in appearance during the Dust storm because the wind speed dramatically increases. This allows dust or sand as you say to move and be deposited elsewhere. But really, I should not have to explain this to you. Sometimes I can be the Master of the obvious.:-)

http://qt.exploratorium.edu/mars/opportunity/micro_imager/2004-02-10/1M129692504EFF0322P2953M2M1.JPG

http://qt.exploratorium.edu/mars/opportunity/micro_imager/2004-03-15/1M132625446EFF0602P2956M2M1.JPG

You are correct. It looks sandy to me too. It looks like its made out of the same stuff. Sorry about that. I sometimes get confused when talking about the dust or rather sand on Mars.

Posted by: denis Jul 7 2007, 09:58 PM

QUOTE (dburt @ Jul 6 2007, 11:48 PM) *
For me the only key observation about the spectrum of sizes is the strict size limitation at about 5 mm. Condensation-related impact spherules are entirely different from the shaped splash droplets called tektites, as covered in a previous post. I don't offhand know of a detailed morphological analysis, but would be surprised if one had not been done, perhaps by someone in another forum.


I agree that the hard limit in size at 5-6 mm is a key observation. Also, it has been observed and discussed on another forum that the size distribution of the berries in or near the crater outcrops, or the berries which are protected from the environment in the craters, exhibit a tail towards small diameters. No Earth analogy of this feature has been proposed. This property is not clearly seen for the berries of the plains, which are generally of smaller diameters, and may have suffered weathering.
Although the implications of this asymmetry is not clear to many of us, I do think that it is not incompatible with a condensation scenario in an impact surge cloud.
Distinctive morphological details have also been discussed : dimps, seams etc.. To me an account of these features in a surge hypothesis seems much more problematic.

denis

Posted by: nprev Jul 7 2007, 10:42 PM

QUOTE (denis @ Jul 7 2007, 02:58 PM) *
Distinctive morphological details have also been discussed : dimps, seams etc.. To me an account of these features in a surge hypothesis seems much more problematic.

denis

Welcome, Denis! smile.gif Agreed, and esp. since the anomalous small-scale features you cite seem to be much more prevalent on berries that are embedded in sedimentary strata or under the soil (recall those seen in the trenches dug by Oppy early in the mission). If they are condensates rather than accretions, then I am at a loss to explain their symmetry, unless they somehow formed VERY rapidly while airborne or suspended in solution; haven't seen any 'pristine' berries with a flat side, for example.

Posted by: don Jul 8 2007, 02:11 AM

"Other Don - That's all well and good, but many things are theoretically possible (including little green men, perhaps). Just show me the evidence, please. More to the point, are there any features at Meridiani (or Gusev, or any of those many other salty layered deposits all around the Mars highlands) that CAN'T be accounted for by the impact surge hypothesis?"


HDP Burt

I agree, green men are possible right up there with impact surge- the structure of your debate on impact surge seems to include any and all features can be linked to a surge. If there was a kitchen sink observed in an outcrop I'm sure there is an explanation for it with impact surge. Do salts in a nonequallibrium condition at endurance point directly to impact surge? Of course not. Do hematite spheres? No. What is the evidence for impact surge, just show us the evidence, please! Difficulties or simply holes in the MER theory are not allowed. wink.gif

"the other Don"

Posted by: Kye Goodwin Jul 8 2007, 03:59 PM

tdemko, Thanks for your reply 154. It is good to get confirmation that single-particle layers do occur in turbidites and base-surge deposits. You seem to have included base-surge among sub-aqueous processes. Do you think of base surge as a sub-aqueous process? I have read some descriptions that make much of the presence of liquid water in creating the surge layers and other sources that do not mention liquid water at all. I resumed my net search on this topic in the last few days and found a 30 year old Wolletz and Sheridan paper that includes a few lines that spell out how the planar beds were thought to form in base-surge:

“Still further from the vent the cloud deflates to the point where inertial flow dominates and void space is generally less than 60%. Here grain collisions set up shear plains along which grains of different sizes seek their respective zones of lowest shear energy and inversely graded planar beds result.”

That reference to shearing layers has been very hard for me to find and confirms the explanation that I have been using. Unlike many layer-forming processes this one involves the simultaneous presence of a stack of unfinished layers all in motion together and interacting. Herr Doctor Burt seems a little bored with these details, but I think that they may be important in changing minds, especially in explaining impact-surge to non-scientists. Surge isn’t a magic cloud that makes layers but it does make layers in a way that is very unfamiliar to most people, that they can't hope to visualize without some help.

Here is the address of that paper. I hope it works. If not, sorry about my bad net skills on a new site and new browser.

http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1976LPICo.259..157W&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf

Posted by: dvandorn Jul 8 2007, 04:15 PM

QUOTE (Kye Goodwin @ Jul 8 2007, 10:59 AM) *
“Still further from the vent the cloud deflates to the point where inertial flow dominates and void space is generally less than 60%. Here grain collisions set up shear plains along which grains of different sizes seek their respective zones of lowest shear energy and inversely graded planar beds result.”

This statement, if it is a currently accepted postulate for how planar beds are formed during basal surges, is quite well-suited for testing in re the Meridiani deposits.

It predicts that, for each surge event, you should see inversely graded planar beds. In other words, the largest grains should make up the first beds deposited, followed by progressively smaller grains until the uppermost layers are made up of the finest grains. (At least, that's my reading of what "inversely graded" means.)

Has Oppy found such an inverse grading relationship between the beds in the units it has been able to study? Since the theory above uses as a basic theorem that the layering is entirely due to different grain sizes sorting out, there ought to be an observable change in grain sizes from layer to layer. Even if this delta is so small as to be difficult to measure from one layer to another, it ought to have been enough over the depth of the unit observed within Endurance to be able to be quantifiably observed.

So -- here's a direct test of your theory, Herr Doktor. It's even a test on which you can do a little non-rigorous work using the raw JPG images from back during the Endurance campaign (or more rigorous work using the images already released to the PDS). I have to say, I truly think that if anything of this sort had been observed at the time, we would have heard about it... but I'm prepared to be proven wrong on that if you want to try and pursue this proof.

-the other Doug

Posted by: tdemko Jul 8 2007, 07:38 PM

"Normal" grading is coarsest grain size at the base, finest at the top. Inverse grading is finest grain size at the base, coarsest at the top. Normal grading approximates what you might see from simple gravitational (Stokes) settling.

Aeolian pinstripe lamina are inversely graded due to winnowing of wind ripple crests...fines are trapped in the troughs and the coarser crests bury this material during migration. Debris and turbidity flows that accelerate rather than decelerate during deposition would also be inversely graded.

I threw in the comment about lamination in base-surge deposits as an afterthought. I think that pyroclastic and base-surge flows act differently from both subaqueous and subaerial sediment transport processes. The evolution of hot gases in the flow during transport and deposition make characterizing the hydro/aerodynamics complex and unpredictable, to say the least.

Posted by: dburt Jul 9 2007, 01:29 AM

QUOTE (nprev @ Jul 7 2007, 03:42 PM) *
Welcome, Denis! smile.gif Agreed, and esp. since the anomalous small-scale features you cite seem to be much more prevalent on berries that are embedded in sedimentary strata or under the soil (recall those seen in the trenches dug by Oppy early in the mission). If they are condensates rather than accretions, then I am at a loss to explain their symmetry, unless they somehow formed VERY rapidly while airborne or suspended in solution; haven't seen any 'pristine' berries with a flat side, for example.


Nprev (and Denis) - Been taking most of the weekend off from Mars, but have a few minutes now. Just a couple of comments: 1) There are no really comparable deposits on Earth (only volcanic surges, which are real wimps by comparison, and form under vastly different conditions. 2) I suspect that some of the features you describe formed as post-depositional coatings, affected by local bedding - I would only pay attention to the appearance of spherules after any salty coatings have been brushed off by the Rover. Even then, a symmetry (of say a belted waist) is hardly inconsistent with accretion in a cloud. 3) Unlike some people whom I won't name, we don't pretend to have all the answers. smile.gif

--HDP Don

Posted by: dburt Jul 9 2007, 01:47 AM

QUOTE (don @ Jul 7 2007, 07:11 PM) *
I agree, green men are possible right up there with impact surge- the structure of your debate on impact surge seems to include any and all features can be linked to a surge. If there was a kitchen sink observed in an outcrop I'm sure there is an explanation for it with impact surge. Do salts in a nonequallibrium condition at endurance point directly to impact surge? Of course not. Do hematite spheres? No. What is the evidence for impact surge, just show us the evidence, please! Difficulties or simply holes in the MER theory are not allowed. wink.gif

"the other Don"


I disagree with your general philosophy - there were so many inconsistencies and internal contradictions in the MER team theory that we felt compelled to come up an alternative - and this is the best we could do, given our collective backgrounds. Perhaps it's wrong - we almost certainly have some details wrong. I'm open to any and all suggestions for improvement. As for the evidence, it is all around - Mars is drowning in impact craters, of all ages and sizes, hitting any imaginable target composition. It's also drowning in layered sulfate-rich sediments. Both rovers have found almost identical-appearing features in such sediments (including spherules), currently ascribed to completely different causes. If you wish to ignore the hydrosphere (mainly a cryosphere, near the surface) and atmosphere of Mars, and think that impacts on Mars are identical in their affects to those on the Moon (ballistic ejecta only) feel free. Rampart craters, unique to Mars, suggest you would be wrong. If you think that Mars cratering never produced fines, other than a bit of dust and sand on the surface, and that these never were deposited into rocks, other than those deposited by a secondary agent (water or wind or volcanic reworking- never impact surge) feel free. Occam's razor (the simplest explanation consistent with ALL the data, in Einstein's formulation) favors only impact surge, in my admittedly biased opinion. If you think it favors the MER team explanation, or if you reject it as a general philosophy, please explain why.

That's all for now - gotto go eat.

--HDP Don

PS (just ate): Surge is perfectly capable of eroding, transporting, and depositing a kitchen sink (which is more than I can say for the wind); putting it on Mars in the first place might present be a slight problem, though. Outflow channels - no problem moving and depositing it either.

Posted by: dburt Jul 9 2007, 02:55 AM

QUOTE (dvandorn @ Jul 8 2007, 09:15 AM) *
.

So -- here's a direct test of your theory, Herr Doktor. It's even a test on which you can do a little non-rigorous work using the raw JPG images from back during the Endurance campaign (or more rigorous work using the images already released to the PDS). I have to say, I truly think that if anything of this sort had been observed at the time, we would have heard about it... but I'm prepared to be proven wrong on that if you want to try and pursue this proof.

-the other Doug


Other Doug - I'm glad Tim Demko has joined this discussion - I hope he feels free to contradict what I say. My impression from when I first learned about inverse grading in volcanic surge deposits nearly 30 years ago was that it was observable mainly in near-vent, coarse-grained deposits consisting of blocks and lapilli of many cm to many mm. In far-out deposits consisting primarily of well-sorted, sand-sized grains you would not expect to see it. No inverse grading has been observed or described from the sandy surge deposits at Home Plate, for example, and yet the MER team is calling them volcanic surge deposits (owing to the presence of a single possible "bomb sag" - there is no volcano apparent, no tear-drop-shaped lava "bombs" have been seen on the surface, and the basaltic bulk composition - and occasional ballistic ejecta sags - are to be expected for practically any impact surge deposit on Mars). So are you suggesting that they are mistaken too? If not, please explain your logic. Thanks for the good ideas, BTW.

--HDP Don

Posted by: MarsIsImportant Jul 9 2007, 04:36 PM

How do you explain the near pure silica deposits found by Spirit? How would that fit in with impact surge?

Posted by: Kye Goodwin Jul 9 2007, 06:53 PM

MarsIsImportant, Re your 165, There is no necessity for impact-surge to explain the concentrated silica found at Gusev. It is a tricky mental exercise, I know, but try to consider the evidence of the layering in isolation from the chemical evidence. A hypothesis should explain all the facts but the facts are always in various degrees of doubt. It is a really solid fact that the layered structure at Meridiani and Homeplate dates from the time when the sediments were laid down. The present chemistry at the surface of these deposits (or near them in the case of the silica) may be the product of processes that have little to do with the original deposition. I don’t think that either theory should have to account for the present-day chemistry at Meridiani or Gusev primarily by invoking ancient processes, because we do not know how old that chemistry is or how deep it goes. Endurance Crater is being considered as if it were a fresh drill core but it has probably been part of the surface weathering environment for hundreds of millions of years. The deepest RAT hole hasn’t even reached through the material that is heated diurnally by the sun. The layered structure of the rock is certainly deep but the chemistry could be that of a weathering rind centimeters to meters thick. There is likely some of the original material present as reaction products but even considerable replacement is possible at the surface, which is all that we have seen. Kilometers of chemically complex dust has settled on these surfaces over Mars history in close contact with even more frost. In high-obliquity periods the surface may be covered with a thin layer of dirty snow that comes and goes annually.

The MERs have added very little to the STRUCTURAL evidence of bulk liquid surface water or near-surface groundwater. There are the ambiguous festoons at Meridiani, and the planar layering believed by the MER team to have resulted from many similar shallow flooding events on very level ground. The evidence of water CHEMISTRY, on the other hand, is overwhelming but the form in which the water acted is unknown as is the time period when the chemicals formed. I think that slow processes involving ice, vapor, adsorbed films, water of hydration and even possibly fleeting liquid capillary water from melting frost, might account for the chemical alterations. Without the chemical evidence, the structural evidence of persistent surface water would be completely unconvincing, even to the MER team I would guess. The two kinds of evidence should be considered separately because they are not equally reliable. The structural evidence of the layering tells us something about the process of deposition at Meridiani and Homeplate. The chemical evidence from the present-day surface may not tell us much at all about the time when the deposits formed.

Posted by: MarsIsImportant Jul 9 2007, 10:08 PM

Kye that was a good reasoned response. That fact is that we don't know all the circumstances in which this near surface water chemistry took place. We don't know for sure (not 100%) whether this was a very local occurrence or evidence of water chemistry in bulk. But the mere fact that we found this evidence within a few kilometers from the landing site suggests that it is rather common on the surface of Mars.

It certainly does not rule out impact surge as an explaination; but it certainly is not helpful to that hypothesis either. It proves that additional processes have altered parts of the surface since these layers were laid down. It certainly gives me confidence in what the MER team has suggested as the explanation at Meridiani too, simply by implication.

Yes, much of the MER team's evidence for their hypothesis is circumstantial. Yet, the circumstantial evidence keeps building. To rule out impact surge or confirm it, we need a prediction that can be tested by the rovers. I know science is not exactly a court of law; but many people are convicted upon mere circumstantial evidence. If the circumstantial evidence has substantial weight, then chances of error become very low. When circumstantial evidence is backed up by empirical evidence, it becomes very strong of a case indeed! In my eyes, the evidence of some sort of water chemistry occurring on or near the surface combined with the circumstantial found so far makes the case almost conclusive. At this point, I see no reason to doubt the MER teams's conclusions.

In my opinion, the impact surge or brine splat hypothesis maybe a contributing factor to the complexity of the geology on Mars. I don't doubt that, given the enormous number of visible craters on the surface. I do doubt the impact surge hypothesis as an explanation of the evidence found at Meridiani so far. Although very thin deposits would be possible with an impact surge, many are not that thin. In fact, we should have already seen evidence of some thick layers at Meridiani, if the impact surge explanation was even plausible. At this point even if we find thick layers laid down much deeper, it still will not rule out the current MER team consensus. It will only place constraints upon time frames for the various processes involved.

Posted by: dburt Jul 9 2007, 10:10 PM

QUOTE (MarsIsImportant @ Jul 9 2007, 09:36 AM) *
How do you explain the near pure silica deposits found by Spirit? How would that fit in with impact surge?

Kye - Thanks for your thoughtful and philosophical reply to this post. Let me try to answer it much more directly (although I may have already stated this in a previous post): As far as I can tell from the images, the silica-rich rocks are loose pieces sitting on top of the surge deposits, along with various chunks of highly vesicular (gas bubble-filled) and totally non-vesicular (bubble-free) rock. Therefore they need have nothing to do with the surge deposits. They and the other loose surface rocks most likely are random pieces of impact ejecta, of unknown ages, from unknown sources. The silica-rich rock presumably indicates some sort of hydrothermal activity, but whether associated with water (or ice) interacting with a volcano or associated with water/ice interaction with impact melt, would be impossible to say. The silica-rich rock, as another conceptual possibility, might have formed at low temperature by silicate rock reaction with sulfuric acid formed during sulfide weathering (my mine dump model), as a result of acid leaching of the more basic constituents (MgO, CaO, etc.). Again, not necessarily anything to do with the surge process. If a hydrothermal system had interacted with the surge deposits themselves, they would all most likely have been turned almost instantly into clay-rich goo, owing to their highly reactive and porous and permeable nature. Good question - I hope this was a good answer. smile.gif

--HDP Don

Posted by: MarsIsImportant Jul 9 2007, 10:24 PM

Yes, that was a good answer Professor Burt. But much of these silica deposits are in the form of sand. So they cannot be ejecta pieces. A few silica rocks indeed have been found and could correspond to what you just stated. But the sand or dust like 90% pure silica require a longer term water based solution in my eyes.

I supposed it could simply be local because of hydrothermal activity; but that is similar to what the MER team has stated.

Your answer was helpful however. Thank you.

Posted by: dburt Jul 10 2007, 12:02 AM

This thread seems to be decaying into the same non-specific objections by just a few people. Does this mean that everyone else reading this agrees with the reasonableness impact surge hypothesis, in light of Occam's Razor? In hopes of providing some fresh material for discussion, I attach, from March 2006, a detailed critique by Squyres et al. of our original 2005 Nature paper, and our point-by-point attempted rebuttal of that criticism. After sending the critique and our response out to two reviewers, Nature decided not to publish it (although they did publish a critique of the competing volcanic surge model). I therefore feel justified in "publishing" it here, as an attachment. This is particularly so because the Squyres critique (but never our response) was for a long time published on the Cornell website, here: http://www.astro.cornell.edu/~banfield/nature2.pdf (link since removed), without giving us any ability to respond. Also, the MER team has repeatedly used these highly dubious points (e.g. the spurious idea that Fe/Ni ratios in iron meteorites must match those in the spherules) in allegedly "refuting" the impact surge hypothesis in publications, even though, IMHO, we demonstrated these objections to be utterly without merit well over a year ago. Note: be aware that this pdf file (short and hopefully not too technical) is a time capsule from over a year ago. Our insights have evolved since then, in part owing to my past several weeks of highly useful discussions here.

One example of an insight not mentioned in the file is the simple fact that all the Meridiani spherules consist uniquely of the high temperature form of hematite - the blue/gray or "specular" (shiny) form. This, the main reason why Oppy landed in Meridiani, appears to provide unambiguous evidence against the low-temperature concretion hypothesis of the MER team. Although this point was as plain as the nose on my face, looking through my own eyes, I didn't see it for years, until I had discussed things on this forum (a form of mirror). Thanks.

Please enjoy or feel free to mock.

--HDP Don

 1_reviewer_attachment_2_1143837763.pdf ( 41.2K ) : 259
 

Posted by: dburt Jul 10 2007, 12:25 AM

QUOTE (MarsIsImportant @ Jul 9 2007, 03:24 PM) *
But much of these silica deposits are in the form of sand. So they cannot be ejecta pieces. A few silica rocks indeed have been found and could correspond to what you just stated. But the sand or dust like 90% pure silica require a longer term water based solution in my eyes.


Um, to what sand or dust of 90% pure silica are you referring? All I recall seeing in images are broken rocks (some of them quite tiny pieces, but no more than you would expect from breaking a weak piece of impact ejecta as it landed or grinding it under the rover wheels). None of the high-silica rock seems to be "in place." Thanks (and all for now).

--HDP Don

Posted by: MarsIsImportant Jul 10 2007, 12:54 AM

...Very interesting arguments Professor. Many of the issues brought up in the attachment have been discussed already, sometimes at length. It does give us a better idea of why you seem frustrated. Some of your counter-arguments are good.

I still have not changed my mind. But this discussion may be useful.

I must point out that silence does not indicate affirmation. Despite the common rumor among salesmen, many people simple don't want to argue. That does not mean that the customer actually agrees; they just don't want to create confrontation.

Posted by: MarsIsImportant Jul 10 2007, 01:01 AM

QUOTE (dburt @ Jul 9 2007, 07:25 PM) *
Um, to what sand or dust of 90% pure silica are you referring? All I recall seeing in images are broken rocks (some of them quite tiny pieces, but no more than you would expect from breaking a weak piece of impact ejecta as it landed or grinding it under the rover wheels). None of the high-silica rock seems to be "in place." Thanks (and all for now).

--HDP Don


http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070628a/Sol1198A_P2539_L257F_br.jpg

Sorry but there is no way that the rover could possibly crush these deposits to such fine grains. There are image examples where the rover has crushed some silica rocks. They don't resemble this at all.

Posted by: dburt Jul 10 2007, 01:13 AM

QUOTE (MarsIsImportant @ Jul 9 2007, 06:01 PM) *
Sorry but there is no way that the rover could possibly crush these deposits to such fine grains. There are image examples where the rover has crushed some silica rocks. They don't resemble this at all.


Um, again (I came back online). Are those really silica rocks? They sure look like crushed subsurface sulfate efflorescences to me - something that Spirit has been seeing more and more of since it broke its wheel. Please don't confuse high-albedo soft sulfates with high-albedo hard silicates. (Or is it I who am confused?) Thanks.

--HDP Don

Posted by: MarsIsImportant Jul 10 2007, 01:24 AM

QUOTE (dburt @ Jul 9 2007, 08:13 PM) *
Um, again (I came back online). Are those really silica rocks? They sure look like crushed subsurface sulfate efflorescences to me - something that Spirit has been seeing more and more of since it broke its wheel. Please don't confuse high-albedo soft sulfates with high-albedo hard silicates. (Or is it I who am confused?) Thanks.

--HDP Don


http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070628a.html

It is clearly marked as fine grained silica. This was the biggest and best discovery of the entire mission and it was very recent. I am correct.

Posted by: dburt Jul 10 2007, 01:53 AM

QUOTE (MarsIsImportant @ Jul 9 2007, 05:54 PM) *
I still have not changed my mind. But this discussion may be useful.

I must point out that silence does not indicate affirmation.


Thanks for your kind comments. I am not asking you to change your mind - only open it.

As someone who has been teaching for a while, I am well aware that a class full of sleeping students does not indicate that they all agree with me. Sometimes I have to give them a quiz to wake them up. Inasmuch as you seem to have appointed yourself spokesman for the sleepers, how would you, for example, explain 1) the high-temperature (blue/gray) hematite in the blueberries, if they are actual low temperature sedimentary concretions, not to mention 2) why they are strictly size limited to 5 mm diameter, unlike actual concretions, 3) why they are not shaped like actual concretions, being generally perfect spheres, 4) why they never clump together like actual concretions (just the odd doublet or triplet of small spherules, explainable by natural stickiness and growth in a cloud), 5) why their distribution is apparently never controlled by fluid migration paths, inasmuch as fluid migration and mixing is how actual concretions form, 6) why they are characteristically nickel-enriched (keeping in mind the arguments in our Nature rebuttal), or 7) why similar appearing (albeit smaller) spherules are locally abundant at and near Home Plate, if that outcrop has an entirely different origin? Take as much time as you need, and feel free to work in groups. This is a take-home exam for the entire class. Good luck. smile.gif

--HDP Don

Posted by: dburt Jul 10 2007, 02:03 AM

QUOTE (MarsIsImportant @ Jul 9 2007, 06:24 PM) *
http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070628a.html

It is clearly marked as fine grained silica. This was the biggest and best discovery of the entire mission and it was very recent. I am correct.

You are quite correct about the quote (and my impression about sulfates, based on the image alone, was apparently wrong). I am still apparently correct that it is a loose soil, of unknown origin, sitting on top of whatever rocks lie underneath. If future investigations show that it is part of an outcrop, and not just an orphaned bit of soil, then its parentage will have possible genetic significance. Otherwise it's just another Mars mystery. But defininitely score one for your team.

--HDP Don

Posted by: MarsIsImportant Jul 10 2007, 02:15 AM

Well, I cannot speak for those who sleep. However, let me again state that the limited and consistent size of the spherules is your best argument--that in the absence of any known nearby volcanic source. That has bothered me from the beginning of the mission.

I cannot really explain it. My mind has been open all along.

Knowing how big some of the volcanoes on Mars are, I wonder whether the less gravity would allow surge clouds to travel much further than expected. But I cannot explain the distribution of the berries either. It doesn't seem to make sense--whether it is volcanic surge, impact surge, or concretions. I think there is a missing major piece of evidence that opportunity needs to find. Whether it will ever find such a piece of evidence is hard to say. Spirit did not find the silica until very recently, and only because of a broken wheel. Maybe Opportunity needs to lose a wheel in a place that it can dig deep too. I don't know where that could possibly be. Perhaps when it is inside Victoria.

Posted by: djellison Jul 10 2007, 07:10 AM

QUOTE (dburt @ Jul 10 2007, 01:02 AM) *
Does this mean that everyone else reading this agrees with the reasonableness impact surge hypothesis,


Absence of objection doesn't mean evidence of support. cool.gif

Doug

Posted by: ngunn Jul 10 2007, 09:27 AM

Well, I for one find all this very interesting, even though my lack of relevant knowledge means I'm a million miles away from actually holding an opinion.

Sadly, however, I note that we are now 'students' who have been given 'homework' and even for the brighter ones an occasional 'mark' !!! This is an excellent strategy for deterring rather than encouraging intelligent comment. Why oh why do you do it, dburt?

Posted by: denis Jul 10 2007, 10:12 AM

HDP Don,

One fact is missing from your class exam smile.gif . As I mentioned earlier, we have shown on another forum that the size distribution of the berries is asymmetric, with a left-sided excess of particles. This has been consistently obtained for both MI and Pancam observations (*). I consider now this feature as correlated to the hard upper limit in size.
In your opinion, does the impact cloud condensation hypothesis, where the dropplet growth may be limited by gravity, fit with these observations ? I am anxious to get you comment on this particular point. Thanks.

denis

(*)
http://geocities.com/rlewis6/Spherule_Database.htm
http://www.geocities.com/jnelson351/statistics_paper.html
http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1001.pdf

Posted by: marsbug Jul 10 2007, 01:37 PM

I was infamous for dozing off during lectures, but this one has kept my attention very well. biggrin.gif To switch metaphors I think the brine splat hypothesis has gone the full 15 rounds and come out of its corner fighting every time. Certainly its true that it has been unfairly dismissed in some quarters. I would still say my gut reaction (and very possibly my earth bound predjudices) tell me that to account for several billion years of surface evolution with only one process is stretching even the best idea, but I can't find any specific objection. My gut, which is very talkative today because my brain knows little about either geology or chemistry, also finds the idea of a mars which is cold and slightly damp for a long time easier to digest than one which was recently warm and very wet. So congratulations Herr Professor, I'd say impact surge is a convincing alternative. I hope you can find time to post on some of the other discussions. I'd be very interested to hear your opinions on the features and processes of Titan for instance.

Posted by: djellison Jul 10 2007, 03:14 PM

QUOTE (marsbug @ Jul 10 2007, 02:37 PM) *
I hope you can find time to post on some of the other discussions.


Brine splat stuff stays in this thread however.

Doug

Posted by: centsworth_II Jul 10 2007, 03:57 PM

I don't know if anyone has yet referenced the "Not a base surge" section at the end of
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3292.pdf presented at the http://www.lpi.usra.edu/meetings/7thmars2007/
I'm happy to see these issues formally addressed by the MER team. I see the arguments
as being in three categories:

1) "Regional geological context... no evidence for age-appropriate impacts of
sufficient size."

2) The berries: a) "Fe/Ni levels are inconsistent with such an impact origin."
b) "...spherules are dispersed across all strata, even at obvious erosional
surfaces..."

3) "Stratification styles" that "are most consistent with low velocity, subcritical
flows, characteristic of fluvial and eolian transport.

I have a hard time fitting the stratification models in my head, so I settle on
the berry distribution argument as the one I best understand.


HDP Burt, tell me where my reasoning is faulty here:

If there are layers, with erosional discontinuities in between, and the
distribution of berries across the layers and across the discontinuities
is even, what is the best explanation? That various base surge events
just happened to contain the same distribution of berries, or that the
berries formed after the layers were in place? I think the simplest
explanation is the second.

Posted by: MarsIsImportant Jul 10 2007, 04:31 PM

I think the berries forming after the layers were laid down is the simplest explanation too.

The more I think about it, the possibility exists that the missing clumped berries that Professor Burt asks about might actually exist. Opportunity may simply not have found a good example yet. If Meridiani is primarily a current aeolian erosion area, then most clumps near the surface might have been dispersed already. So the only realistic way to find these clumps is to dig.

The other problem is the apparent limit in size of the berries. Some quick change must have stop the process that created them. Perhaps the condition that created them was marginal at best. So the quick change didn't need to be as drastic and quick as it sounds. Perhaps in other areas of Meridiani there are much larger berries. We won't know until we visit those areas.

Edit: I know that Spirit has found some clumped berry like feactures in certain rocks. It was long time ago and it would take some time to dig the images out. But they are there. Gusev is not Meridiani. But Like I said previously...we still might not have found good examples of them at Meridiani yet.

Posted by: MarsIsImportant Jul 10 2007, 06:15 PM

I was looking thru Opportunities Micro-Imager files to find before and after images of the magnets on the rover. I found something very interesting that relates to the discussion of spherules.

They have been looking for the clumped masses of concretions that we have assumed were missing in this discussion. The MER team must have known that the spherules was their weakest point in the hypothesis. I now believe they have found good evidence of these missing clumped masses. I've found more than doublets and triplets in the files. I suddenly noticed that some of the larger spherules were actually composed of many many smaller spherules glued together!!! I was surprised to see that many clumped together. I have not gone through all the files yet. But I believe they have found plenty of evidence to provide the 'smoking gun' for their wet Meridiani theory. The MER team seems to be ready to provide the empirical evidence they needed.

Edit: Look in the May 2007 files for the Micro-Imager to see what I'm talking about. There are a LOT of images.

Posted by: hendric Jul 10 2007, 06:20 PM

Dr. Burt,
One big difference between Earth and Mars is the presence of life here. Maybe the Martian concretions are how they would grow on a lifeless world, but here the growth is more irregular due to bacterial contamination in the water or sand? Perhaps in a lifeless environment concretions do not form as readily as here on Earth, so the volumetric density is not as high preventing conglomerations, and the growth is more even allowing for spherules instead of flattened discs?

http://www.daviddarling.info/encyclopedia/E/endolith.html

I guess that option doesn't reduce the number of "dead grandmothers", but it does open up some possibilities. smile.gif

Has anyone tried creating concretions? I found a semi-crankish site on the web that said nobody has, but the tinfoil-hattery was everywhere (concretions and blueberries are formed by electric discharge!). It would be interesting to try to create concretions with well water (with appropriate added salts) and dune sand vs distilled water and sterilized sand.

Do we know how long the it takes concretions to form?

Posted by: centsworth_II Jul 10 2007, 10:50 PM

QUOTE (Kye Goodwin @ Jul 10 2007, 03:12 PM) *
Doug Ellison, Thanks for asking. It will be a long haul ...

I hope you start you own thread as you mentioned.
This thread should just be for questions and comments
to Dr. Burt.

Posted by: dburt Jul 11 2007, 01:54 AM

QUOTE (ngunn @ Jul 10 2007, 02:27 AM) *
Well, I for one find all this very interesting, even though my lack of relevant knowledge means I'm a million miles away from actually holding an opinion.

Sadly, however, I note that we are now 'students' who have been given 'homework' and even for the brighter ones an occasional 'mark' !!! This is an excellent strategy for deterring rather than encouraging intelligent comment. Why oh why do you do it, dburt?

Only to provoke a response from you and Doug, and thanks to both of you for yours. Also, to misquote Arne in T2 again, "Of course. I'm a professorator." - I've been programmed, after 35 years. I can't help that. I just hope no extra grandmothers die during the quiz biggrin.gif (if you followed the beginnings of this thread).

--HDP Don

Posted by: dburt Jul 11 2007, 02:44 AM

QUOTE (denis @ Jul 10 2007, 03:12 AM) *
As I mentioned earlier, we have shown on another forum that the size distribution of the berries is asymmetric, with a left-sided excess of particles. This has been consistently obtained for both MI and Pancam observations. I consider now this feature as correlated to the hard upper limit in size.
In your opinion, does the impact cloud condensation hypothesis, where the droplet growth may be limited by gravity, fit with these observations ? I am anxious to get you comment on this particular point. Thanks.


Denis - Great question, and of course I am utterly unqualified to answer it. Luckily, my co-author Ken Wohletz filled with the gap (what else are co-authors for?) with an e-mail containing the following quote:

I did a sequential fragmentation/transport analysis on the referenced
data. To my surprise, the distribution of berry sizes is almost perfectly
described by an SFT distribution with a mode at -2.22 phi and
dispersion value of 0.39. Dispersion values greater than zero generally
indicate aggregation (rather than fragmentation); thus my results suggest
that his observations perfectly support an accretionary hypothesis.

It's all pig-Latin to me, but that definitely sounds like a yes for accretion. Contact him for more details. In a later message he added the following general words of wisdom:

I seem to get that one of the problems readers have with the impact surge
hypothesis is that thousands of layers of similar thickness seen in
Meridiani suggest thousands of surges all depositing similar layers. It is
very important to get across the idea that a single surge may wax and wane
hundreds of times at any single location during its runout, resulting in
deposition of numerous layers. This phenomenon comes from the breakdown of a
shock wave into a train of hundreds of waves because of shock reflections
off of the substrate, off of internal density contrast surfaces, and off of
each other. Think of thunder and how the sounds rolls, cracks, and rumbles
all from one lightning stroke moving through air of different density,
temperature, and moisture content. The flow regime in a surge is a response
to a pressure gradient, and that pressure gradient is analogous to a sound
wave. So just like thunder, some surges can be loud and short lived, while
others can be prolonged starting with a crack but followed by numerous
booms.

So yup, that's why we all need co-authors. smile.gif

--HDP Don

Posted by: dburt Jul 11 2007, 02:55 AM

QUOTE (marsbug @ Jul 10 2007, 06:37 AM) *
... So congratulations Herr Professor, I'd say impact surge is a convincing alternative. I hope you can find time to post on some of the other discussions. I'd be very interested to hear your opinions on the features and processes of Titan for instance.


Marsbug - Thanks for waking up, and thanks even more for the compliment. smile.gif As for being profound about Titan, I'm already partly faking it here (as you may have noticed), so consider it unlikely unless I stick strictly to P-chem aspects (and even then you'd have to provide me with the relevant phase diagrams).

--HDP Don

Posted by: MarsIsImportant Jul 11 2007, 03:29 AM

Thank you Professor,

You finally addressed my biggest problem with the surge idea. You showed how it is not necessarily a problem at all.

If the surge made so many thin layers, then how would we distinguish between it and the wet Meridiani model?

Posted by: Kye Goodwin Jul 11 2007, 05:22 AM

It seems that Dr. Burt and his co-author are having some success in changing minds. I wish that more Unmanned Spaceflight readers would tell us where they stand.

Posted by: dburt Jul 11 2007, 05:23 AM

QUOTE (centsworth_II @ Jul 10 2007, 08:57 AM) *
I don't know if anyone has yet referenced the "Not a base surge" section at the end of
one of the MER papers presented at the Seventh International Conference on Mars.
I'm happy to see these issues formally addressed by the MER team. I see the arguments
as being in three categories:

1) "Regional geological context... no evidence for age-appropriate impacts of
sufficient size."

2) The berries: a) "Fe/Ni levels are inconsistent with such an impact origin."
cool.gif "...spherules are dispersed across all strata, even at obvious erosional
surfaces..."

3) "Stratification styles" that "are most consistent with low velocity, subcritical
flows, characteristic of fluvial and eolian transport.

I have a hard time fitting the stratification models in my head, so I settle on
the berry distribution argument as the one I best understand.
HDP Burt, tell me where my reasoning is faulty here:

If there are layers, with erosional discontinuities in between, and the
distribution of berries across the layers and across the discontinuities
is even, what is the best explanation? That various base surge events
just happened to contain the same distribution of berries, or that the
berries formed after the layers were in place? I think the simplest
explanation is the second.


Centsworth - Congratulations on doing independent research. I believe you're the first to mention that particular long meeting abstract (which appears to be the first ever to acknowledge the prevalent Meridiani interpretation as "a model"). Regarding your item 1) I seriously doubt this, inasmuch as relative age is assigned solely by superposition (what's on top of what) and the assumption of original horizontality. These assumptions work rather well for "wimpy" deposits deposited by wind and water (or for ballistic ejecta on the Moon). A large impact surge could completely cover low spots such as craters, giving them an apparently young crater count age, yet completely scour even slightly earlier deposits off the nearby heavily cratered highlands (as stated in a previous post to you), giving them an anomalously ancient apparent age relative to the nearby lowlands. Also, I imagine he is basing his size statement on 1) the wrong assumption that the Meridiani exposures had to result from a single large distant impact and 2) the conventional wrong assumption that impact deposits only reach about 2 crater diameters out. Models are only as powerful as the assumptions that feed them (classically known as "GIGO" - garbage in, garbage out). That's why I prefer stick with observations, where possible.

Regarding 2a), as stated in previous posts, even if the spherules are oxidized iron condensates (which we mentioned in 2005 as only one possibility among many), we regard their assumption that the Fe/Ni ratio in vapor-condensed accreted spherules has to match that in Fe-Ni meteorites as completely mistaken and misleading (see our unpublished Nature critique refutal attached to my post 170 above) - there is no conceivable reason why there should be a match. More to the point, despite special pleading to the contrary (see, e.g., abstract 3231 at the same meeting), they cannot explain why water-deposited hematite, containing only Fe3+, should be at all enriched in Ni2+, given that Ni2+ at Meridiani had so many other favorable crystalline sites to go to, such as the Mg2+ sites in Mg-sulfates or silicates. Look up, e.g., the terrestrial literature on the mineralogy of Ni-laterites (as I believe I mentioned in a previous post). This concept is called "partitioning" and in those terms, Ni2+ is "incompatible" in hematite (should never be enriched). Remember, you're talking about a couple of my supposed fields of expertise here (no co-author needed).

Regarding 2b), as stated in multiple previous posts, I regard the observed pattern of distribution of spherules at Meridiani as a far stonger argument AGAINST the concretion hypothesis than it is for it. Perhaps the author in question should do some more field work in the Page and Navajo sandstones (as I have been doing for the past 3 years), inasmuch as he has made these his favorite Meridiani analogs (apparently based largely on published articles). Actual hematitic concretions there, other than being round, little resemble his model - e.g., they're commonly concentrated and clumped at erosional surfaces. Let me know if you'd like photographic documentation.

Regarding 3) the "stratification styles" such as so-called "festoons" that are allegedly unique to wind and water - haven't we already beaten that one near to death in previous posts? (I'd be happy to try to put it out of its misery, but only if specifically requested).

Regarding the allegedly even distribution of berries - certainly not true at the large scale, and at the small scale I remain satisfied by my prior analogy of injecting them with sand into a turbulent jet exhaust (little reason to separate, and every reason to mix). Keep in mind that once berries are formed, later impacts could further distribute and mix them across an even wider area and thicker stratigraphic interval (as must have occurred at Victoria Crater, prior to wind erosion). If wind ever concentrated them as a lag at the surface, as today seen at Victoria, later surges could scour and mix them in with the rest of the particles. Of course, at the extreme far end of the surge run out, as things calmed down, they might well be concentrated as a lag along bedding planes, but even that seems not strictly to be required (as in a perfect condensation dump-out, for example). One shouldn't confuse what is sometimes seen in wimpy little volcanic surges with what might be expected big he-manly impact surges biggrin.gif (with apologies to Arne and SNL). All you Ph.D. clastic sedimentologists, please feel free to contradict me - like any professor, I sometimes make this stuff up as I go along...

Regarding their hematitic composition (thanks for not bringing that up again too smile.gif ), my co-author Ken Wohletz today shared these general words of wisdom:

It is not uncommon that volcanic accretionary lapilli vary in composition
with the matrix in which they finally reside; the reason being that they
have sampled a different portion of the ejecta plume than what is mainly
represented in the surge. Lapilli can form high in the atmosphere, fall out
into a moving surge, and experience horizontal transport before being
deposited. The "sampling" process involved with accretionary lapilli is
complex and depends a lot on electrostatic potentials that are in turn
compositionally dependent. Thus it is entirely possible that accretionary
lapilli can grow by preferentially accreting particles of a specific
composition. These results are covered by an experimental study done by
Schumacher a number of years ago.

More or less equal to what I randomly made up in response to previous posts, but in much fancier words. Ain't co-authors wonderful? rolleyes.gif

BTW, the morning session of this upcoming Friday the 13th in Pasadena seems to have some the most relevant MER presentations - sorry I won't be there. Perhaps some of you who will be can comment afterwards, or I can comment on some more of the abstracts. Apologies to the rest, this is all I have time for now.

--HDP Don

Posted by: dburt Jul 11 2007, 05:56 AM

Here's a final one before I go home (before the subject gets completely lost in the crowd).

As regards Ken's pig-Latin in my post 198 about berry size distributions, here's some more pig-Latin from him in a subsequent e-mail:

I stand by my analysis but cannot vouch for the
quality of the data used. In fact in all my years of applying SFT to natural
samples, I have not seen one so perfectly explained by SFT than these
blueberry sizes.

The fact that the distribution is perfectly unimodal is eye-catching; most
natural samples demonstrate some degree of polymodality caused by mixing of
fragmentation and/or transport processes. The fact that the distribution
dispersion value (gamma includes sorting, skewness, and kurtosis) is
positive strongly supports an aggregation process (smaller particles
sticking together to form larger ones tends to make a distribution more
peaked with a decreased fine tail).

An aggregation origin predicts a rather limited size range, with a mode
giving a hydrodynamic equivalent for turbulent suspension in a multiphase
fluid. If one observes average blueberry size of 4 to 5 mm over a wide
range, then one might suggest that the bulk Reynolds number in surges was
fairly constant, a situation possibly coming from runout over a surface of
fairly constant surface roughness and elevation. Other hypotheses from surge
theory can also be tested. One I like is the self-limiting process of
deposition, which tends to keep Re steady in some surge runouts.

Hey, I didn't even make that one up out of whole cloth first (I couldn't even if I tried). All I can say is it sounds like the original poster should contact him ASAP about possibly writing a paper together...

Whatever happens, remember, you read it here first!

--HDP Don

Posted by: MarsIsImportant Jul 11 2007, 02:57 PM

QUOTE (Kye Goodwin @ Jul 11 2007, 12:22 AM) *
It seems that Dr. Burt and his co-author are having some success in changing minds. I wish that more Unmanned Spaceflight readers would tell us where they stand.


My mind has not changed, just because I ceded one point of contention. The professor did not change his mind when he ceded one to me earlier. I never expected him to change his mind about his surge hypothesis. I also anticipated his response of the possibility of erosion of an ejecta piece in the area of home plate as an explanation for the silica sand found recently.

Just because something is deemed possible in one particular respect does not mean it is probable. It only adds a small amount of credibility to an alternative argument. It simply raised the scenario from the realm of impossibility in my mind to one of possible but unlikely. I'm sure the Professor feels the same way about his concession to my point. Yet, such concessions are expected, else this issue would not be given the room for argument on this forum.

Posted by: djellison Jul 11 2007, 03:07 PM

A straw poll (and given the nature of forum software, such things are easily done ) of the two main rock formation theories would be an interesting thing. I think it's only fair to give HDP's hypothesis more airing time, and then we could do a poll to see which camp people fall down on.

Doug

Posted by: MarsIsImportant Jul 11 2007, 03:21 PM

Yes, Professor you have addressed the topic before. But you concentrated on how features observed coincided with those predicted by your surge hypothesis. That seems to make your scenario somewhat possible in those respects (I'm temporarily discounting objections for other reasons). But those same characteristics of those features also coincide with the MER team's explanation. Differences in interpretation of the same features cannot distinguish between the two competing theories.

What I'm looking for are distinguishing characteristics of your explanation that would not be present given the MER team's wet Meridiani scenario...or vice versa. This would offer a test to determine which hypothesis is more probable. A predicted distinguishing feature that can be observed would turn this argument away from a 'he said she said' like confrontation.

Posted by: don Jul 11 2007, 03:27 PM

dBurt – back to the sulfates: You’ve stated often that you have a problem with the latest MER scenario that: “requires maintenance of a highly acidic aquifer in rocks containing basaltic materials” (unpublished response to response Knauth, Burt and Wohletz). You feel the neutralization capacity of the basalt wouldn’t allow this imbalance. You reference Zolotov 2005 to support of your point. However in a recent abstract of Zolotov (Lunar and Planetary Science 2007) the point is made that “acid weathering on early mars probably player a larger role……”. Apparently he doesn’t have a problem with longer duration acidic conditions. As you have pointed out by the presence of neutral salts, neutralization eventually occurs, but after what period of acidity? He also discusses the role of large impacts as a cause of acid weathering. Another abstract by Benison et al (Seventh Int. Conf on Mars) discusses the geochem and mineralogy of mars and makes a good case for extended acidic conditions even in the presence of mafic rocks. Do I hear the sound of rock hammers chipping away at this once solid foundation ? tongue.gif

"the other don"

Posted by: denis Jul 11 2007, 04:56 PM

HDP Don re#190,195

Thanks so much for your input. Looks like our questions encounter a resonator with Dr Wohletz biggrin.gif . I would like to know to which data on berries sizes he is refering to. I will try to figure out what is the significance of his SFT distribution parameters (phi, dispersion), as compared to our more conventional ones (mean, skewness). What impress me is his statement for a signature of an accretion scenario.

denis

Posted by: MarsIsImportant Jul 11 2007, 08:34 PM

Let's just assume for an instant that the impact surge hypothesis were correct (that's a temporary assumption).

The hematite spherules are like hail stones. Shouldn't they create some type of minor bomb sagging evidence within the layers of deposits? This should be observable with the Micro-Imager on the rover. I know of no such disturbance within the layered deposits. Just because such a disturbance has not been identified yet, is no indication of whether they are actually there--unless somebody actively searched for such evidence. Perhaps this was the basis for the MER team ruling out the volcanic surge process in the formation of the spherules.

If I remember correctly, somebody stated there was no indication of disturbance within the layers caused by the spherules. Doesn't that highly suggest that the spherules were created in place? If the spherules would not create a disturbance in the layers during the impact surge, then why not? What is so different about an impact surge from a volcanic surge that would prevent such disturbances?

Edit: http://volcanology.geol.ucsb.edu/saltlake.gif

http://volcanology.geol.ucsb.edu/hydro.htm

"Bedding sags form by the impact of ballistically ejected bombs, blocks and lapilli upon beds capable of being plastically deformed. They are common in hydroclastic deposits of many maar volcanoes, tuff rings and tuff cones. Beds beneath the fragments may be completely penetrated, dragged down and thinned, folded, or show micro-faulting (Heiken, 1971). Deformation is commonly asymmetrical, showing the angle and direction of impact if three-dimensional exposures are available. These differ from dropstones in glacial environments in that dropstones fall perpendicular to the bottom, symmetrically indenting bedding and rarely, if ever, penetrating."

The spherules would be the lapilli in this case.

Posted by: dburt Jul 12 2007, 02:13 AM

QUOTE (MarsIsImportant @ Jul 10 2007, 09:31 AM) *
The more I think about it, the possibility exists that the missing clumped berries that Professor Burt asks about might actually exist. Opportunity may simply not have found a good example yet. If Meridiani is primarily a current aeolian erosion area, then most clumps near the surface might have been dispersed already. So the only realistic way to find these clumps is to dig.

The other problem is the apparent limit in size of the berries. Some quick change must have stop the process that created them. Perhaps the condition that created them was marginal at best. So the quick change didn't need to be as drastic and quick as it sounds. Perhaps in other areas of Meridiani there are much larger berries. We won't know until we visit those areas.

Edit: I know that Spirit has found some clumped berry like feactures in certain rocks. It was long time ago and it would take some time to dig the images out. But they are there. Gusev is not Meridiani. But Like I said previously...we still might not have found good examples of them at Meridiani yet.

MarsIsImportant - Do dig out that evidence please, as you did so well for the silica-rich soil. In the Navajo and Page Sandstones, hematitic nodular clumps up to meters across weather out as readily as individual concretions - no digging necessary. More readily, in fact - they form erosion-resistant benches. (I always prefer to cite observational evidence, rather than my general predjudices about how things ought to behave.) Your second argument is that some sort of "quick change" must have stopped the process that formed them. If so, why did it apparently stop at exactly the same time uniformly over the entire 100's of square kilometers of Meridiani - or (using direct observations by the rovers) the more than 10 kilometers of Oppy traverse, including rocks many meters deep?

What kind of "magic process" did you have in mind? I can think of no terrestrial analog offhand, or anything implicit in the extant Meridiani model that would allow it (one of my numerous problems with that model). Remember that concretions grow many meters deep in the rock, cutting them off from any conceivable weather variations. You can't stop them with a freshwater influx, because that would dissolve all the soluble Mg-sulfates that cement the rock (although such an improbable dilution is how the MER team hypothesis suggest that the hematite replaced jarosite in the first place). Also, the brines would never mix - the freshwater would sit essentially forever on top of the salt water, as in terrestrial coastal areas (another problem I have with the MER team hypothesis). Your "magic cut-off process' reeks of a 7th dead grandmother to me (i.e., rather super-special pleading), especially if you have no examples in mind for a possible process.

Next time ask me a specific question - then I probably won't ask you one. smile.gif

--HDP Don

Posted by: dburt Jul 12 2007, 02:18 AM

QUOTE (denis @ Jul 11 2007, 09:56 AM) *
HDP Don re#190,195

Thanks so much for your input. Looks like our questions encounter a resonator with Dr Wohletz biggrin.gif . I would like to know to which data on berries sizes he is refering to. I will try to figure out what is the significance of his SFT distribution parameters (phi, dispersion), as compared to our more conventional ones (mean, skewness). What impress me is his statement for a signature of an accretion scenario.

denis - I told you everything I know. I presume it is data he pulled off the web links in your original post (#181). Contact him for more info (although he may read this eventually).

HDP Don

Posted by: MarsIsImportant Jul 12 2007, 02:50 AM

Absence of evidence is not evidence of their absence. But even if those clusters are not there, that simply means it is a Martian mystery. Mars is not Earth.

If there are no major clusters at Meridiani, your alternative has even larger obstacles to overcome. The spherules must have been created in a low temperature environment. Kye pointed out this source for that supposition and it makes a lot of sense. It is only one piece of evidence; but it is strong.

http://www.gps.caltech.edu/~tglotch/glotch_fresnel.pdf

Edit: Sorry for jumping around my thought processes, but...

There is also no apparent asymetrical distortion within the bedding layers around the individual spherules. That should be another problem for the impact surge hypothesis. But then again. Mars is not Earth. It has less gravity. So Absence of evidence is not evidence of their absence. We need to look harder in an effort to be sure we didn't miss something.

Meanwhile, I'll do my best to dig up more evidence. And if I stumble onto something that supports the impact hypothesis, then I will share it here. It doesn't matter to me what the truth is; I'm just searching for it.

Posted by: dburt Jul 12 2007, 03:46 AM

The server having been overloaded temporarily, I just deleted a duplicate post. That leaves me space to mention:

Why doesn't someone ask me if the impact that formed Victoria Crater produced a surge? (The one-word answer would be yes. Expounding, Oppy must have driven right over it, given that there's orbital evidence that some remains, and not recognized it.)

--HDP Don

Posted by: dburt Jul 12 2007, 03:48 AM

QUOTE (don @ Jul 11 2007, 08:27 AM) *
dBurt – back to the sulfates: You’ve stated often that you have a problem with the latest MER scenario that: “requires maintenance of a highly acidic aquifer in rocks containing basaltic materials” (unpublished response to response Knauth, Burt and Wohletz). You feel the neutralization capacity of the basalt wouldn’t allow this imbalance. You reference Zolotov 2005 to support of your point. However in a recent abstract of Zolotov (Lunar and Planetary Science 2007) the point is made that “acid weathering on early mars probably player a larger role……”. Apparently he doesn’t have a problem with longer duration acidic conditions. As you have pointed out by the presence of neutral salts, neutralization eventually occurs, but after what period of acidity? He also discusses the role of large impacts as a cause of acid weathering. Another abstract by Benison et al (Seventh Int. Conf on Mars) discusses the geochem and mineralogy of mars and makes a good case for extended acidic conditions even in the presence of mafic rocks. Do I hear the sound of rock hammers chipping away at this once solid foundation ? tongue.gif

"the other don"

Other don - Misha Zolotov (a colleague in SESE at ASU) has heard me give various talks on impact surge perhaps more times than anyone alive except Paul Knauth, and he is beginning to listen. His original (2005) statement that we cited still holds - impossible to maintain acid groundwater in a basaltic regolith (simple common sense, although he did some calculations, and others have done experiments). His LPSC abstract this past March took what I had said about impacts into abundant Fe,Ni-sulfide deposits (the abundant sulfide deposit idea originated with Roger Burns - we just added impacts, as in my mine dumps article) and about various gaseous sulfur species, in addition to steam in the surge cloud (also mentioned in my mine dumps article) and proposed a great deal of post-impact acid rain - a catastrophic flood of acid. He recognizes that this acid soon would be neutralized. This suggestion does not require target sulfides, BTW - only sulfates, and in fact it was made long ago w.r.t. the dinosaur-killing impact at Chicxulub Crater, Mexico, where the target rocks were rich in Ca-sulfates. The "catastrophic acid rain" suggestion is probably irrelevant for Meridani, where there is absolutely no sign of surface runoff, such as a catastrophic rain would produce (and the MER team therefore, quite reasonably, left rain and surface runoff out of its model). Using Occam's Razor, we also left it out of our impact model (although it certainly had occurred to us too). Sulfide weathering or acid steam condensation (also in McCollom and Hynek's volcanic surge model - abstract #3257 at Friday morning' session in Pasadena) seem completely adequate.

Relevant to Benison, D.K. et al. in Pasadena (I presume you are referring to #3376?), what strikes you as particularly Mars-like about those acid lakes? Is it that they appear to be chloride-dominated, unlike the surface of Mars? Is it that the hematitic concretions look like normal concretions, unlike the berries? Is it that by far the dominant salt precipitated is the least soluble one, gypsum, which forms pure white effloresecences, which can be picked up by the wind (very locally only) and forms white dunes? (Unlike the most soluble Mg-sulfates that dominate Meridiani.) Is it that the deposits are rich in kaolinite and other crystalline clays, as might be expected (and that presumably you'd find typical playa lake beds of clays if you trenched them), unlike Meridiani, which utterly lacks lake beds or crystalline clays? Is it that acid persists in schists and amphibolites - regional metamorphic rocks probably utterly lacking on Mars (although they might exist somewhere very, very deep inside Mars)? Is it that they specify no source of acid (but other literature specifies constant replenishment via sulfide weathering - as we propose, following Burns). I could go on and on, but perhaps you get the idea. Yes, if you cut it off from any contact with a basaltic regolith, or wind-blown dust or sand, and provide an unknown surficial source of acid (e.g., volcanic acid mist or impact-related rains), you might form a very temporary acid evaporite lake on Mars - but then you might expect to see some signs of there having been a lake. Where is it? (Meridiani is very large.) If an alien civilization had colonized Mars, they might have built monoliths, but where are they? As I concluded an earlier reply, many, many, many things are theoretically possible for Mars, including acid lakes and little green men, but please, please specify your evidence. (Jarosite is only a mineral, which usually forms via sulfide weathering on desert mine dumps or in gossans - which is how Roger Burns suggested it might form on Mars. Us too.) Thanks.

BTW, I think there's ample evidence of impact cratering on Mars, ample evidence that impact cratering produces size-limited spherules of various types, commonly enriched in Ni (as for Chicxulub spherules), and ample evidence that surge deposits emulate those deposited by wind and water. There's also every reason to expect both abundant spherule-containing surge deposits on Mars and their preservation until the present. What other evidence would you like? Note that a model NEVER constitutes direct evidence of what happened - only of what might have happened. Also remember w.r.t. models - GIGO. Also remember Occam's Razor, as restated by Einstein (choose the simplest hypothesis that explains everything). The MER team hypothesis, in addition to being the most convoluted imaginable, fails, IMHO, to account for all the evidence (athough to give them credit, they really, really tried). Ours does, so far as I yet have learned. biggrin.gif

Sorry to rant - you seem adept at pushing my buttons. And keep chipping away - I'm truly grateful for your efforts.

HDP Don

Posted by: CosmicRocker Jul 12 2007, 04:43 AM

QUOTE (dburt @ Jul 9 2007, 07:02 PM) *
This thread seems to be decaying into the same non-specific objections by just a few people ...
Dr. Burt, you nailed it. That is precisely why I have tried to stay out of this debate, in spite of my desire to rant and rave about various points. By forcing all of this discussion into this one thread, it has become a tangled mess of competing and disparate ideas. It seems to me that breaking specific conversations out into separate threads in the Mars topic would provide a natural order to this brawl, allowing one to more clearly weigh the merits of the indivdual contributions. There have been some very insightful comments made as well as (dare I say) a few clueless ones. I am only suggesting that we should create some order from this chaos.
...One more thing...did the impact that formed Victoria form a surge? ...without a doubt, and the MER team has already announced that they intend to investigate a proximal contact from that event as soon as they are able to command this little robot to enter the crater.
QUOTE (djellison @ Jul 11 2007, 10:07 AM) *
A straw poll (and given the nature of forum software, such things are easily done ) of the two main rock formation theories would be an interesting thing. I think it's only fair to give HDP's hypothesis more airing time, and then we could do a poll to see which camp people fall down on. ...
That would be fun, and maybe more fun if we could see which way we each voted. cool.gif

Posted by: dburt Jul 12 2007, 05:18 AM

QUOTE (MarsIsImportant @ Jul 11 2007, 07:50 PM) *
Absence of evidence is not evidence of their absence. But even if those clusters are not there, that simply means it is a Martian mystery. Mars is not Earth.

If there are no major clusters at Meridiani, your alternative has even larger obstacles to overcome. The spherules must have been created in a low temperature environment. Kye pointed out this source for that supposition and it makes a lot of sense. It is only one piece of evidence; but it is strong.

http://www.gps.caltech.edu/~tglotch/glotch_fresnel.pdf

There is also no apparent asymetrical distortion within the bedding layers around the individual spherules. That should be another problem for the impact surge hypothesis.


MarsIsImportant - You are correct that absence of evidence is not evidence of absence. On the other hand, Oppy has been driving over spherules for 3.5 years, along a traverse of over 10 km, and has imaged literally millions of them. So we have a pretty good statistical idea of what they are really like - see yesterday's posts. I could show you more variation in 10 minutes, over 10 meters of outcrop, sampling only a few hundreds of concretions, anywhere on this planet, I dare say. Certainly that's true at the sites that have been cited as Mars analogs (concretions in the Navajo and Page Sandstones of N. Arizona and S. Utah).

Statistically, the blueberries are like flipping a coin, and getting 500 heads in a row. You could always argue that the next flip might give you a tail, but at some point you have to suspect that somebody might be pulling a fast one on you - i.e., that they handed you a two-headed coin (heads on both sides). Let's just say that at this point I'm statistically pretty confident that you could flip that coin for the rest of your life, and never, ever, come up tails. My co-authors and I early on suspected that Mars might be pulling just such a fast one on Oppy and its team, so we tried to come up with an alternative hypothesis. Can you conceive of a two-headed coin, even if you've never encountered one? Time to check it out, don't you think?

I have reread the Glotch et al. article that you cite (I did so when you mentioned it on the other thread). You apparently fail to understand just what it is they are claiming. Not my field either, of course, but I think the key point is understood by looking at their Figure 10 on the last page. All that they claim to have DISPROVED by spectroscopy is a completely random orientation of platy hematite grains - this "A" is a straw horse, unreasonable to anyone who knows crystals. What they claim to have PROVED is "B" - that the c-crystallographic axis [001] of the hematite flake is radial to the center (in other words, that the flakes are arranged like those in a cylinder of paper you would get by rolling it up). This is the way a concretion might grow - but it is also the only way that an accetionary lapillus made of tiny hematite flakes might grow (as I have mentioned in many previous posts - roll 'em up like a snowball). If the spherules hadn't grown this way, they wouldn't be shiny or specular on the outside. What Glotch et al. fail to discuss is why a sedimentary concretion would consist of shiny blue-gray hematite (the specular form) in the first place. They claim to have grown some hematite at high temperatures by some unspecified process - but it wasn't a hydrothermal brine or salty steam, as far as I know. I think they probably just dry roasted red hematite. In this case as in many others (including part "A" of that figure), they picked their own straw horse to shoot at - they're certainly not shooting at us or at anything we ever claimed as a possibility. That part is not particularly great science, IMHO.

BTW, very enterprising of you to look that reference up. My compliments. It just doesn't prove what you thought. It only explains why the spherules are shiny (they contain shiny flakes that are facing outwards), which anyone with the least understanding of crystallography already knew. smile.gif It does NOT explain why they are blue-gray, as far as I can tell, and it certainly doesn't disprove anything we've ever claimed.

--HDP Don

Posted by: nprev Jul 12 2007, 06:32 AM

blink.gif ...sounded pretty convincing to me!

However, why couldn't a less catastophic 'unimodal' process repeat itself many times (i.e., short-duration groundwater flooding events) and produce similar results? If other influences such as wind erosion (presumably minimal by our standards over medium time frames) and precipitation (utterly absent) are nullified, wouldn't this tend to generate much more uniform berry distribution if for no other reason than that the process is much simpler than its terrestrial analogs?

Posted by: dburt Jul 12 2007, 06:53 AM

QUOTE (MarsIsImportant @ Jul 11 2007, 08:21 AM) *
What I'm looking for are distinguishing characteristics of your explanation that would not be present given the MER team's wet Meridiani scenario...or vice versa. This would offer a test to determine which hypothesis is more probable. A predicted distinguishing feature that can be observed would turn this argument away from a 'he said she said' like confrontation.

MarsIsImportant - These are pretty obvious, and I've already stated them many times. If Oppy were to find actual lake beds, that would provide positive evidence for the vanished lake hypothesis. If it found large, non-spherical berries, or multiply clumped berries, or berries related to fluid passageways, that would provide positive evidence for the concretion hypothesis (the shiny, blue-gray nature would still be totally unexplained, as would the elevated Ni content). If it found huge salt crystals, or their casts or imprints, such as typically grow beneath the surface in playas (or anywhere else that salts are soaked in brines) that would provide positive evidence for the soaked-in-a-brine hypothesis. If it found actual mud (especially mud containing mud cracks), that might provide positive evidence for the interdune playa at a water table hypothesis. If it found braided stream channels, or other types of independent evidence of flowing water, that would provide positive evidence of the highly ambiguous (IMHO, completely non-existent) "festoon problem" (just look at them "festoons" in the middle of the cliff at Cape St. Mary - my post #79). And so on.

I cannot emphasize this enough - there is NO POSITIVE EVIDENCE for the hypotheses that provide the individual parts to the highly complex extant model, other than the salts (wrong mix and wrong grain size for evaporites - so they had to get the wind to bring them from somewhere else, vanished), cross-beds (ambiguous - but certainly not typical dunes, for the most part), and spherules (millions fail any reasonable statistical test for concretions; the concretion hypothesis cannot explain their Ni content or shiny blue-gray nature).

There already is POSITIVE evidence (based on Oppy observations) for EVERYTHING in the extremely simple impact surge hypothesis (salt mix, all bedding features, shrinkage cracks, spherules and their nature and distribution, impact craters everywhere, related deposits seen from orbit, nearly identical features seen at Home Plate, the whole shebang). You couldn't ask Mars to produce anything more. smile.gif The lack of coarse material (to quote you, absence of evidence is not evidence of absence) is easily accounted for by making the impact target distant or allowing it to be Meridiani-like itself (beat up on Meridiani and you'll get more Meridiani, as predicted by William K. Hartmann in his "kablooey of dust and steam" phrase). The lack of abundant Fe-sulfides (again, absence of evidence is not evidence of absence) seems not a problem - how else than by destroying them are you going to form jarosite or other acid sulfates? (Although acid steam in the surge cloud works too.) The abundance of specular blue-gray hematite in the accretionary spherules is not unexpected for a salty, steamy surge cloud on such an exceedingly iron-rich planet, although I'd predict that other compositional varieties of spherules will also be found. Keep in mind that if there hadn't been something unusual about the Meridiani spherules, Oppy would never have landed there.

The main problem people seem to have (especially you) is they apparently cannot believe that Mars would throw Oppy and its team a fast one - would not meet everyone's prior desires and expectations (i.e., would hand it a two-headed coin to flip, as per my previous post to you). Well get used to it. Begin to suspect. Mars loves to play tricks on our expectations. It's not what we want it to be, it's what it is. It is an alien little planet, after all. That's all for tonight. (And I'd really rather make the debate a little less repetitive tomorrow, else I may have to give another quiz. mad.gif Or would you prefer a classroom demonstration? smile.gif )

--HDP Don

Posted by: djellison Jul 12 2007, 06:55 AM

QUOTE (CosmicRocker @ Jul 12 2007, 05:43 AM) *
It seems to me that breaking specific conversations out into separate threads in the Mars topic would provide a natural order to this brawl,


And as I have said before - no. This remains a theory that is against the mainstream view. Don's efforts are appreciated Other members would have had posts deleted for that sort of behaviour he is getting away with here. We have decided within the admin subforum that this subject should remain within this one thread. He's already recieving more than fair treatment - the condition is that the subject remains contained here otherwise every thread turns into an athena-vs-burt argument, and that's not going to happen. There are other forums which might be more open to a fragmented debate about this issue - this is not one. End of issue.

Doug

Posted by: MarsIsImportant Jul 12 2007, 12:46 PM

Dr. Burt

I have a lot to respond to, so please be patient with me. I may need a series of posts, especially when I start listing out evidence.

First of all, I compliment you for directly pointing out some of the possible faults of the Glotch paper and the source hematite sample used. That was needed, but it still is a strong piece of evidence. The conclusions you attributed to me were not mine. I cannot in all honesty take any credit. Let me quote directly from the Glotch paper itself:

QUOTE
Given the [001] dominated emission of the spherules, it
is likely that they formed at low temperature, thus ruling out
such formation mechanisms as impact melt spherules, volcanic
lapilli, or other mechanisms that do not create hematite dominated
by [001] emission.


I stated myself that it was only one piece of evidence. This was a laboratory experiment and just one comparison study. It is convincing but not absolute. You could always repeat the experiment yourself using a hematite sample that you feel is more appropriate.

....more posts to follow soon.

Posted by: MarsIsImportant Jul 12 2007, 01:57 PM

...to respond to post #210

Dr. Burt

This may take a long time and many, many posts. Let me state that I had hoped to stay on topic target by discussing primarily your alternative hypothesis. I had hoped that you would provide distinguishing characteristics that would be found only if your alternative was more correct...distinctive characteristics that would reasonably be found from an impact surge, yet not with the mainstream theory. Instead of offering tests for your own hypothesis, you continually offer up only tests for the mainstream hypothesis. To be fair, you did list supposed positive evidence for the impact surge, yet everyone of them is POSITIVE evidence for the mainstream hypotheses if you interpret those features differently. So none of them provides any distinguishing characteristics. I must conclude now that I should not expect any. Is this fair? Well, there is no good Earthly analog to your impact surge hypothesis; so maybe some of these characteristics are difficult to predict. It's your hypothesis; but, I suspect that I should try to come up with some of my own.

I appreciate your listing the characteristics expected if the mainstream hypothesis is more correct. It will help tremendously, primarily because it is all in one place. It is rather a long list. I will deal them one at a time.

Before I get into them, I would like to point out that you did not respond to my one previously proposed test for your hypothesis. You did seem to respond to that particular post but not to the proposed test(unless I missed something). Unless you object, I will assume that it is a good test.

...to quote myself

QUOTE
Edit: http://volcanology.geol.ucsb.edu/saltlake.gif

http://volcanology.geol.ucsb.edu/hydro.htm

"Bedding sags form by the impact of ballistically ejected bombs, blocks and lapilli upon beds capable of being plastically deformed. They are common in hydroclastic deposits of many maar volcanoes, tuff rings and tuff cones. Beds beneath the fragments may be completely penetrated, dragged down and thinned, folded, or show micro-faulting (Heiken, 1971). Deformation is commonly asymmetrical, showing the angle and direction of impact if three-dimensional exposures are available. These differ from dropstones in glacial environments in that dropstones fall perpendicular to the bottom, symmetrically indenting bedding and rarely, if ever, penetrating."

The spherules would be the lapilli in this case.


We should see some sort of evidence similar to this, if the impact scenario is more on target.

Not all of the lapilli would be expected to completely solidify before hitting the ground. So we should also expect some evidence of deformity of some spherules that is indicative of impact. I know of no examples. I will be on the look out for them.

This whole process will take some time. This will require a good deal of primary research. And it must be done on my spare time. Please understand that I also have a day job that must be attended to. So, this may take quite a bit of time.

Posted by: ngunn Jul 12 2007, 02:15 PM

A quickie - Why only haematite? Where are all the 'hailstones' made from the many other materials that presumably condense out of an impact surge in similar fashion? Oh . . I know - leached away by groundwaters.

Posted by: silylene Jul 12 2007, 02:27 PM

QUOTE (djellison @ Jul 11 2007, 03:07 PM) *
A straw poll (and given the nature of forum software, such things are easily done ) of the two main rock formation theories would be an interesting thing. I think it's only fair to give HDP's hypothesis more airing time, and then we could do a poll to see which camp people fall down on.

Doug


I am far from being a geology expert, but I am a chemist.

I don't understand why the argument is one...or the other. I haven't seen any reason why both mechanisms could be operant at different times, and/or why one excludes the other. It does seem to me that "surges" can and do account for some observations, in addition to the MER team hypothesis.

Posted by: MarsIsImportant Jul 12 2007, 02:30 PM

QUOTE (ngunn @ Jul 12 2007, 09:15 AM) *
A quickie - Why only haematite? Where are all the 'hailstones' made from the many other materials that presumably condense out of an impact surge in similar fashion? Oh . . I know - leached away by groundwaters.


Good point.

That shows that both models would have a similar number of dead grandmothers whether we want to admit that or not. It just so happens that some of us want to ignore them.

Posted by: ngunn Jul 12 2007, 02:33 PM

QUOTE (silylene @ Jul 12 2007, 03:27 PM) *
I don't understand why the argument is one...or the other. I haven't seen any reason why both mechanisms could be operant at different times, and/or why one excludes the other.


For the stratigraphy you can argue for a mixture, but the berries are an all or nothing bet. Nobody could seriously propose that half of them are hailstones and the other half concretions. They shout out common origin loud and clear.

Posted by: MarsIsImportant Jul 12 2007, 03:47 PM

It is safe to say that the MER team has already carefully looked at the evidence for all scenarios from the beginning of Opportunity's traverse across Meridiani.

Here is a quote from Steve Squyres in a Press release from February 9, 2004.

QUOTE
"This is wild looking stuff," Squyres said. "The rock is being eroded away and these spherical grains are dropping out." The spheres may have formed when molten rock was sprayed into the air by a volcano or a meteor impact. Or, they may be concretions, or accumulated material, formed by minerals coming out of solution as water diffused through rock, he said.


Meteor impact...sounds like parts of Dr. Burt's model. They already considered it from the beginning.

Posted by: centsworth_II Jul 12 2007, 04:15 PM

QUOTE (MarsIsImportant @ Jul 12 2007, 11:47 AM) *
It is safe to say that the MER team has already carefully looked at the evidence...

I think that it would be inhuman for the MER scientists to be objective. I would
expect them to be advocates for their theories, as Dr. Burt is an advocate for his.
I'd like to hear what more independent geologists specializing in the pertinent areas
are thinking.

QUOTE (MarsIsImportant @ Jul 12 2007, 11:47 AM) *
Meteor impact...sounds like parts of Dr. Burt's model. They already considered it from the beginning.

But did they think of base surge from the beginning?

Posted by: helvick Jul 12 2007, 04:28 PM

Glotch et al 2006 "Fresnel modeling of hematite crystal surfaces and application to martian hematite spherules"

QUOTE
...So,hematite formation processes that occur at high temperatures,or preferentially create hematite crystals with roughly equal amounts of [001] and other rays are less likely to be responsible for the martian hematite spherules. These processes include the formation of impact-melt spherules (Chapman, 2005; Burt et al., 2005) at high temperature, or the high-temperature oxidation of volcanic lapilli (Knauth et al., 2005).

Burt:
QUOTE
What Glotch et al. fail to discuss is why a sedimentary concretion would consist of shiny blue-gray hematite (the specular form) in the first place. They claim to have grown some hematite at high temperatures by some unspecified process - but it wasn't a hydrothermal brine or salty steam, as far as I know. I think they probably just dry roasted red hematite


The point made here that the 2006 Glotch paper fails to explain the details of the high temperature formation process is not quite true - the claim that is initially made on page 10 references findings in an earlier paper that I have yet to find available openly online. There is a pay-per-view link and abstract here http://www.agu.org/pubs/crossref/2004/2003JE002224.shtml and I found a different 2003 LPS article\paper here http://www.lpi.usra.edu/meetings/lpsc2003/pdf/2008.pdfthat may be an early version.* These two seem to constrain the formation to a process at or around 300-400C and appears to exclude higher temperature formation regimes (700C).

I'm a bit surprised at that 300-400C number - that doesn't seem like a particularly low temperature to me and I can't see how that ties up with the rest of the "concretions forming in a brine" hypothesis. Where exactly are we going to find a 300-400C brine?

Anyway my current question for HDP Burt is whether the additional detail in that referenced paper actually does prove that the hematite at meridiani is unlikely to have formed at the types of temperatures implied by impact surge hypothesis.

*<rant> As a complete aside am I the only one who absolutely detests paper based citation\referencing standards that make chasing up references like this such a trial. I know its not something that can be easily fixed but its about time that academia caught up with the 21st century. </rant>

Posted by: MarsIsImportant Jul 12 2007, 05:00 PM

Well, here is a quote from the Glotch paper about the sample used. So some of Dr. Burt's characterization of it was not exactly accurate--unless he is suggesting some fudging somewhere. That's why we repeat experiments over and over again.

QUOTE
3.2. Sample
The hematite sample used in this study is a platy hematite
crystal from Brumado, Bahia, Brazil with a diameter of 2.4 cm
and a thickness of 3 mm. The small thickness of the crystal
posed a problem in measuring the emissivity of the (100)
face, so the crystal was cut into three pieces perpendicular to
the (001) face (c-face) and perpendicular the [100] axis. The
three pieces were then bound together with epoxy so that the
result was a crystallographic (100) face with an effective diameter
of 0.9 cm. The final 0.9-cm sample was polished to optical
smoothness, ensuring specular reflection at infrared wavelengths.

Posted by: helvick Jul 12 2007, 05:10 PM

I don't think that the sample you reference was at issue. The lack of clarity was in relation to the structure of hematite that was formed in an experiment rather than this machined hematite crystal that was used to validate the spectral models.

Posted by: dburt Jul 12 2007, 05:49 PM

QUOTE (nprev @ Jul 11 2007, 11:32 PM) *
blink.gif ...sounded pretty convincing to me!

However, why couldn't a less catastophic 'unimodal' process repeat itself many times (i.e., short-duration groundwater flooding events) and produce similar results? If other influences such as wind erosion (presumably minimal by our standards over medium time frames) and precipitation (utterly absent) are nullified, wouldn't this tend to generate much more uniform berry distribution if for no other reason than that the process is much simpler than its terrestrial analogs?


Good question, nprev. Sure, short duration groundwater flooding events are certainly possible. Almost anything is possible on a planet about which so little is known. However, there is no positive evidence of them anywhere at Meridiani, any more than there is positive evidence of past playa lakes, or flowing surface waters, so why invoke them if you don't need to? Wind erosion/deposition is possible, and obviously important, but wind does not seem to move the berries at all, so you cannot invoke it to make or alter the berry distribution. The simple process that can be repeated as often as you like, any time you like, and can be adjusted to any scale you like, for any target you like, and for which there is abundant evidence everywhere, including Victoria, Endeavor, and Eagle Craters, is impact. It does the work - it can produce absolutely every feature seen. It explains nearly identical features seen at Home Plate, as well as all of the coarser material there (e.g., on Husband Hill). It explains the boulders unexpectedly found to cover most of the northern plains - greatly restricting Phoenix landing sites. It explains the salty strata that are found in many high elevations around the highlands for which water deposition would be improbable to impossible. What bedrock feature found by the two rovers doesn't it explain?

It doesn't explain many other features of Mars - volcanoes, outflow channels, deltas, dunes, etc. I've never claimed it did. I just think its importance has been greatly underestimated in hypotheses - because of our earthly blinders. It's hasn't been an important process on Earth, compared to everything else going on, except for very occasionally (ask the dinosaurs). On Mars, other than wind, it has been the only constant geological workforce for the past 3.8 billion years (this constancy is depended upon for dating Mars surfaces). The other exciting processes (e.g., outflow channels, young gullies, glaciers, volcanoes) are the episodic exceptions, of local importance - analogous to the occasional role of impacts on Earth.

Keep in mind that the two rovers have increased by orders of magnitude the observational restrictions on any hypotheses - they offer the potential to revolutionize our understanding of Mars. To my way of thinking, huge earthly blinders have so far prevented them from doing so. (Have you ever noticed that Home Plate papers never mention Meridiani, and vice versa?) We so much want Mars to meet our earth-centered expectations, and are perfectly capable of increasing the size of our own blinders to maintain those illusions. I don't know about you, but I'm old enough to remember when Venus was a cloud-covered mystery, and anything was possible there too. People, especially science fiction writers, expected it to be a cloud-covered jungle with strange creatures and beautiful maidens. What a disappointment when it wasn't. Well, I think the same is about to happen to the warm, wet early Mars crowd. The utter lack of crystalline clays, and abundance of easily-altered igneous minerals such as olivine and pyroxene (all via orbital and ground spectroscopy), for any time other than at the height of the Late Heavy Bombardment (oldest, most cratered areas), is perhaps telling you something in this regard.

Ask me more specific questions, and I'll give you more specific answers. smile.gif

--HDP Don

Posted by: MarsIsImportant Jul 12 2007, 06:01 PM

Geothite with hematite...it looks fairly Martian to me.

http://ocw.mit.edu/ans7870/12/12.108/f04/imagegallery/lab1/lab1-16.html

...very much like Meridiani, at least in a general sense.

Posted by: ngunn Jul 12 2007, 06:43 PM

Dburt I have a genuine query for you. I'm trying to imagine the haematite hailstone formation process and I'd just like to be clear exactly how you picture it. Apologies if you have already covered this point here.

Are you postulating molten globules rounded by surface tension which then solidify, or spherules built up radially by successive plating of solid material onto a nucleus like the growth of a pearl?

Are both possibilities consistent with your theory, or only the (hotter?) molten version? (Perhaps the other would not happen quickly enough?)

I would imagine that the two would produce quite different crystalline structures and that the latter might resemble concretions more than the former.

Does the Glotch paper claim to rule out just the first process, or both?

Posted by: dburt Jul 12 2007, 07:46 PM

QUOTE (ngunn @ Jul 12 2007, 11:43 AM) *
Dburt I have a genuine query for you. I'm trying to imagine the haematite hailstone formation process and I'd just like to be clear exactly how you picture it. Apologies if you have already covered this point here.

Are you postulating molten globules rounded by surface tension which then solidify, or spherules built up radially by successive plating of solid material onto a nucleus like the growth of a pearl?

Are both possibilities consistent with your theory, or only the (hotter?) molten version? (Perhaps the other would not happen quickly enough?)

I would imagine that the two would produce quite different crystalline structures and that the latter might resemble concretions more than the former.

Does the Glotch paper claim to rule out just the first process, or both?


ngunn - Thanks for asking me genuine, specific questions. I have already covered your first here - various types of vapor condensation processes produce various types of spherules related to impacts, most very small. For the Meridiani spherules so enriched in shiny blue-gray (specular) hematite, spherules built up by accretion (radially) as hematite flakes formed chemically in the condensing steamy, salty cloud seems to work best. Such hematite is extremely common in volcanic fumaroles - even the MER team has an article about it by Morris et al. (2005, EPSL issue on Meridiani). Glotch was a co-author.

In response to your second question, probably not the hotter, molten version. Imagine whatever you like. smile.gif

The Glotch paper rules out 1) random orientation of hematite flakes in the spherules - no one, least of all us, has ever hypothesized this. 2) that dry roasting of hematite to very high temperatures occurred, equivalent to whatever laboratory process he used to produce it. Utterly irrelevant to our hypothesis (steam, even salty steam, does not condense at such high temperatures).

Thanks again for the specific questions. biggrin.gif

--HDP Don

Posted by: dburt Jul 12 2007, 07:53 PM

QUOTE (MarsIsImportant @ Jul 12 2007, 05:46 AM) *
Let me quote directly from the Glotch paper itself:
I stated myself that it was only one piece of evidence. This was a laboratory experiment and just one comparison study. It is convincing but not absolute.

....more posts to follow soon.


MarsIsImportant - What you quote is not any type of evidence but an inappropriate conclusion. You need to learn to recognize the important difference between data and interpretations of that data. It was a probably meaningless laboratory experiment which I have no intention of repeating. Feel free to do so yourself, however - reproducibility of results is the essence of science.

--HDP Don

Posted by: dburt Jul 12 2007, 08:04 PM

QUOTE (ngunn @ Jul 12 2007, 07:15 AM) *
A quickie - Why only haematite? Where are all the 'hailstones' made from the many other materials that presumably condense out of an impact surge in similar fashion? Oh . . I know - leached away by groundwaters.

ngunn - Thanks for the specific question, although it has already been answered here. As an impact surge cloud travels outwards and turbulently mixes with the atmosphere, the vapors in it expand, cool, and condense. As with evaporation in a lake predictably crystallizing a series of salts according to increasing solubility (in the case of sulfates, least soluble gypsum first, and most soluble Mg-sulfate last), so also various things will condense sequentially out of a cloud according to their volatility and the gradual chemical changes occurring. It is entirely reasonable to expect one phase to form at one time and place, and others at other times and places (as in an evaporating lake). If any of the phases formed were highly insoluble, such has hematite, their form would persist unaltered, whereas more soluble condensates, such as salts, would recrystallize after deposition. No groundwaters needed - only a salty, steamy, condensing cloud.

That was pretty good question. smile.gif Thanks again.

--HDP Don

Posted by: dburt Jul 12 2007, 09:04 PM

QUOTE (silylene @ Jul 12 2007, 07:27 AM) *
I am far from being a geology expert, but I am a chemist.

I don't understand why the argument is one...or the other. I haven't seen any reason why both mechanisms could be operant at different times, and/or why one excludes the other. It does seem to me that "surges" can and do account for some observations, in addition to the MER team hypothesis.


Silyene - Indeed, many geological arguments work out that way - both partly right, at least some of the time. In the present case, IMHO, impact surge accounts for everything the rovers have yet found in fine-grained bedrock, so there is no need to invoke any of the complex series of Earth-like events proposed by the MER team. Future observations, such as the finding of lake beds, might change that conclusion. We're not holding our breath in the meantime.

We agree with them that the dissolved salts originally formed in liquid water, via neutralization of acids by bases. No one has ever suggested any other geologically reasonable way to make dissolved salts in large abundance. We also agree (although my co-authors and I brought the problem up first) that the improbable mixture of soluble and insoluble salts cannot be a primary evaporite - some sort of transportation and mixing event must have taken place (impact by us, wind off a vanished playa by them). We finally agree with them that water was essential to form and cement the rock, only we think that the water was condensing steam, and they make it a series of at least 4 different groundwater brines doing various improbable things below and above the surface and leaving no unambiguous trace of their passage. (Can you tell I'm a bit biased? laugh.gif ).

That's not very much we agree on, although if you insist on "following the water", it might be enough to satisfy that sole criterion of mission success. You couldn't make such deposits on the Moon.

--HDP Don

Posted by: ngunn Jul 12 2007, 09:05 PM

And thank you too for the specific answers. So it's the cooler surface-plating process we're to consider. I'd like to know how long you think this takes - indeed how long you think these objects spend above ground between the impact and the deposition. There is presumably no convective cell structure analogous to what keeps terrestrial hailstones airborne in updraughts long enough to get quite large.

You didn't offer an opinion on what the Glotch work excludes and what it doesn't. Maybe someone else could help here.

On the 'why only haematite' question - I did read your earlier post about how the impact surge could sort materials. That's fine, except I wouldn't expect it to be 100 percent efficient. I am aware that Meridiani was selected because of the prior detection of haematite, so yes you could say 'that was where the haematite fell'. But then why would that mean that nothing else fell there in hailstone form? The haematite is the only such species to resist degradation over long periods? Are we talking about one event or many? Is there a signpost up at Meridiani saying 'Only drop haematite here?'. I think that's beginning to sound like special pleading.

At the very least you have been most unfortunate. The only mineral to provide surviving hailstones also happens to be one which habitually forms spherules in another way!

But please believe me - I'm doing my best to take your scenario seriously. Also I'm encouraged that the discussion appears to have 'grown up' somewhat.

Posted by: dburt Jul 12 2007, 09:14 PM

QUOTE (MarsIsImportant @ Jul 12 2007, 06:57 AM) *
...to respond to post #210
Not all of the lapilli would be expected to completely solidify before hitting the ground. So we should also expect some evidence of deformity of some spherules that is indicative of impact. I know of no examples. I will be on the look out for them.

MarsIsImportant - You are confusing your expectations for Mars (or nature in general) with the way it actually behaves. Impact spherules do not impact the ground like hailstones falling through air - this has been covered in many previous posts. They are carried along with the flow and turbulently mixed with everything else. Accretionary lapilli in terestrial volcanic surge deposits never display the microcratering behavior you ascribe to them, despite Earth's more powerful gravity. Why expect that behavior on Mars, if it is never observed in terrestrial analogs? Do your homework please.

--HDP Don

Posted by: MarsIsImportant Jul 12 2007, 09:20 PM

Professor the evidence for groundwater at Meridiani is so overwhelming that I cannot believe you would say what you just did. Previously you admitted that there was groundwater evidence; now you are saying there is no positive evidence for it. You are simply leaving it as an open question; however, it is not. I thought the issue that your model contested was merely against playa lakes and the origin of these sediments. Without groundwater, even your model fails miserably.

I've come to the conclusion that doing research for you is a complete waist of my time. Here is an internet address where you can find all the evidence you need to change your mind about water's role at Meridiani.

http://marsrovers.jpl.nasa.gov/home/index.html

I suggest you look through all the raw images too. That way you don't have to read all of the so called errant interpretations. In those raw images you will find everything that you claim is not there. Good Luck.

Posted by: dburt Jul 12 2007, 10:40 PM

QUOTE (ngunn @ Jul 12 2007, 02:05 PM) *
And thank you too for the specific answers. So it's the cooler surface-plating process we're to consider. I'd like to know how long you think this takes - indeed how long you think these objects spend above ground between the impact and the deposition. There is presumably no convective cell structure analogous to what keeps terrestrial hailstones airborne in updraughts long enough to get quite large.

You didn't offer an opinion on what the Glotch work excludes and what it doesn't. Maybe someone else could help here.

On the 'why only haematite' question - I did read your earlier post about how the impact surge could sort materials. That's fine, except I wouldn't expect it to be 100 percent efficient. I am aware that Meridiani was selected because of the prior detection of haematite, so yes you could say 'that was where the haematite fell'. But then why would that mean that nothing else fell there in hailstone form? The haematite is the only such species to resist degradation over long periods? Are we talking about one event or many? Is there a signpost up at Meridiani saying 'Only drop haematite here?'. I think that's beginning to sound like special pleading.

At the very least you have been most unfortunate. The only mineral to provide surviving hailstones also happens to be one which habitually forms spherules in another way!


Ngunn - My compliments. It is thanks largely to you that this discussion has "grown up" for the moment. In a previous post I hypothesized that minutes to hours might be needed to form the spherules, and that the convective structure might well be the mushroom-type cloud found above large volcanic and nuclear explosions (analogous to a thunderhead forming hailstones by condensation in air). What volcanologists call "column collapse" (or "downburst" in a thunderstorm - forming radial outflowing desert dust storms in Phoenix) seems probable in the low density atmosphere of Mars - this would form a high velocity particulate surge cloud carrying the tiny spherules along with the radial flow.

I already did offer a perhaps too outspoken opinion on the Glotch work. It is irrelevant to the discussion. They constructed their own straw horse and shot some arrows into it. We were always standing elsewhere.

Why mainly hematite? Probably because it is the only (or the dominant) insoluble mineral that formed. Active fumaroles are famous for forming a huge variety of interesting crustiform salt-type minerals by condensation from steam. Once the fumarole has died, what typically survives are only the water-insoluble oxides like specular blue-gray hematite flakes, cubes of black bixbyite, or rounded masses of brown cassiterite - respectively oxides of Fe, Mn, and Sn. You may also get insoluble fumarolic sulfates like alunite (Al) or jarosite (Fe). For special, fluorine-rich magmas that I once spent several years investigating, you can also get insoluble fumarolic silicates like gem topaz and silica phases (and occasional red gem beryl). In the case of Mars impact surge clouds, in addition to salts and brines, you may well have condensed actual hailstones or snow at the far distant, colder end. Ice in small amounts would obviously not survive, especially in the company of salts. Former chloride salts or even ice may be responsible for the crystal-shaped cavities and general high porosity of the Meridiani beds.

As covered in earlier posts, strictly speaking, you only have to drop the hematite spherules in a single area or zone. If the high velocity and turbulent energy of the radially outflowing surge cloud does not distribute them across the whole of Meridiani Planum, later impacts will. Look at what Victoria Crater did to distribute spherules - as I'll probably discuss more fully in a different post. The reason hematite is so obvious at Meridiani probably has more to do with the wind stripping a large planar area uniformly, leaving a lag (we completely agree with the MER team on this) than it does to its original conditions of deposition. Hematite-rich spherules may well be common elsewhere on Mars, just not exposed or too small to form a lag (or perhaps not - no real basis for saying). No special pleading is needed, in any case.

I don't think we've been unfortunate. Oppy has managed to survive long enough to image millions of berries over a 10 km traverse, not just the ones seen initially in Eagle Crater. Statistics now rule them out as concretions, as covered in previous posts. Concretions are nodules, lumps, masses, and ledges formed in a rock by fluid mixing - there are no constraints whatever on their overall shape, maximum size, or degree of aggregation, but they are constrained to be restricted to zones where fluids have flowed and mixed. The observed size and shape properties alone rule the berries out as concretions (as do their elevated Ni content and blue-gray, blue-gray color, and their distribution pattern in the rock). Anyone who claims otherwise is not using his eyes or common sense, IMHO. Do the actual field work yourself on Earth if you disbelieve me - don't let Oppy do all the heavy lifting on Mars. smile.gif Just park at the MacDonald's in Page, Arizona and start hiking north along the Rim Trail...

--HDP Don

Posted by: dburt Jul 13 2007, 02:38 AM

QUOTE (MarsIsImportant @ Jul 12 2007, 02:20 PM) *
Professor the evidence for groundwater at Meridiani is so overwhelming that I cannot believe you would say what you just did. Previously you admitted that there was groundwater evidence; now you are saying there is no positive evidence for it. You are simply leaving it as an open question; however, it is not. I thought the issue that your model contested was merely against playa lakes and the origin of these sediments. Without groundwater, even your model fails miserably.

I've come to the conclusion that doing research for you is a complete waist of my time. Here is an internet address where you can find all the evidence you need to change your mind about water's role at Meridiani.

http://marsrovers.jpl.nasa.gov/home/index.html

I suggest you look through all the raw images too. That way you don't have to read all of the so called errant interpretations. In those raw images you will find everything that you claim is not there. Good Luck.


MarsIsImportant - Umm. What did I just say? I have never denied abundant salty groundwater on Mars. In fact, between 2000 and 2003 I published several papers proposing concentrated subsurface brines when it was politically incorrect within NASA even to mention the b-word. Again, please do your homework. I am just saying that, IMHO, there is no direct physical or chemical evidence that salty acid groundwater ever rose stepwise as a series of different brines through the salty Meridiani cross-beds, flowed ankle- to waist-deep across the level surface making current ripples, and sank back into the subsurface, meanwhile growing uniformly tiny spherical concretions randomly in the rock. There is also, for the moment, no physical evidence of any vanished playa lake. If you dispute this interpretation, please specify what data you are citing, rather than merely citing other scientists' interpretations that may be opposed to mine. I'm already well aware that many scientists choose to disagree with me, for their own reasons.

If you have been "doing research for me" you have a rather strange way of showing it. Still, I am grateful for your thoughtful comments and for the chance they have given me to lecture you on the nature of science. Unfortunately, that's too much like what I get paid to do every day. sad.gif When I'm not getting paid for it, I would much prefer to answer specific questions and clarify points about our impact hypothesis.

Like you, I'm well aware of that web site and have been following it almost daily since Spirit and Oppy landed (although I admit to getting behind ever since I started spending all my spare time on this web site - which is how you caught me on the silica question). Unlike you, possibly, I try not to confuse data (images, spectra, chemistry, inferred mineralogy) with interpretations of that data. It's not difficult on that site.

Well, best wishes, and back to Mars impacts...

--HDP Don

Posted by: tfisher Jul 13 2007, 03:38 AM

I've been doing a little reading to try to catch up on this thread. (I'm not there yet; there really is a lot of content here!) Anyway, I just wanted to point out the MER team's response to the original "brine splat" paper. This brief article doesn't seem to be up anywhere google can find, other than google's own memory of it: http://google.com/scholar?q=cache:www.astro.cornell.edu/~banfield/nature2.pdf+ (Apologies if I'm duplicating.)

The original paper has been referenced at some point in this thread, but here it is again to read side by side:
http://www.ees1.lanl.gov/Wohletz/Knauth-Burt-Wohletz.pdf

Posted by: dburt Jul 13 2007, 03:48 AM

QUOTE (helvick @ Jul 12 2007, 09:28 AM) *
I'm a bit surprised at that 300-400C number - that doesn't seem like a particularly low temperature to me and I can't see how that ties up with the rest of the "concretions forming in a brine" hypothesis. Where exactly are we going to find a 300-400C brine?

Anyway my current question for HDP Burt is whether the additional detail in that referenced paper actually does prove that the hematite at meridiani is unlikely to have formed at the types of temperatures implied by impact surge hypothesis.


helvick - Sorry for the delay in getting to you. In the meantime, I believe I've already answered your question. Glotch dry roasting things to 700 C, or even 300 C, is probably irrelevant, inasmuch as salty steam condensation probably occurs at lower temperatures, and he didn't grow anything hydrothermally, as far as I can determine. I fully agree with you that 300-400 C is just a bit warm to be growing sedimentary concretions, even in Phoenix in the summer, let alone Mars in the subsurface (where temperatures are multi-year averages, winter and summer).

He wrote that 2004 JGR paper you cited (which he perhaps now regrets, as we all do former hypotheses) when Meridiani was hypothesized to be a large metamorphosed iron formation, heated to 300 C some time after sedimentary deposition, in order to account for the specular or high-temperature blue-gray nature of the hematite as determined from orbital spectroscopy (an earlier hypothesis had been a super-giant hot spring). Once the concretion hypothesis for the spherules was born shortly after Oppy landed, the high temperature nature of the blue-gray hematite in them was not mentioned again, as far as I am aware. (And I admit again that my co-authors and I had quite forgotten about it until my posting here started those creative juices flowing again...). smile.gif Hematite in actual sedimentary concretions is generally reddish-brown, BTW, as I have mentioned previously.

As usual, congratulations on seeking out the original references.

--HDP Don

Posted by: hendric Jul 13 2007, 05:45 AM

I might have missed too much of the discussion already, but here are some of my thoughts on the dead grandmothers:

  1. Brines moving up and down/disappearing: The obliquity on Mars changes much more severely and quickly than on Earth, due to not having a large moon. When the climate gets cold enough, the water in Meridiani froze out, then migrated to the poles, drying out the beds. When the climate warms up again, the returning water doesn't necessarily have the same composition as pre-ice age.
  2. Porosity of the rocks: The freezing at the end of each cycle drives the grains apart, preventing them from sealing shut.
  3. Distribution of the spherules + lack of solid masses of spherules: How well do we understand concretion creation (say that ten times fast!)? Do they require a "seed" at the center? If so, the seeds could be relatively uncommon, transported to Meridiani by wind, mixed with the sand/dust of the layers. Their relatively low abundance would not allow for large masses of concretions. The Navajo sandstone has another thing going for it: life! They've found life deep underground; the distribution of concretions in the sandstone could be modified by life in the rock, or in the original sand. See http://geology.utah.gov/online/pdf/pi-77.pdf
  4. Not enough odd shapes (individual concretions): The shapes of the concretions are driven by the environment. I see no problem with more round concretions due to
    1. Lower gravity on Mars
    2. Lower depth of burial on Mars
    3. Porous rock
  5. Specular hematite: Sorry, my grandmother passed away. Can I get a pass? smile.gif
Did I miss any?

Posted by: dburt Jul 13 2007, 06:27 AM

QUOTE (tfisher @ Jul 12 2007, 08:38 PM) *
I've been doing a little reading to try to catch up on this thread. (I'm not there yet; there really is a lot of content here!) Anyway, I just wanted to point out the MER team's response to the original "brine splat" paper. This brief article doesn't seem to be up anywhere google can find, other than google's own memory of it: [url=http://google.com/scholar?q=cache:www.astro.cornell.edu/~banfield/nature2.pdf+]Squyres
http://www.ees1.lanl.gov/Wohletz/Knauth-Burt-Wohletz.pdf


tfisher - Thanks for the links, and for the confirmation that the criticism, never published by Nature, had been posted on the web, without our response. The criticism and our point by point responses, likewise never published, are attached to my earlier post from a few days ago.

--HDP Don

Posted by: dburt Jul 13 2007, 07:11 AM

QUOTE (hendric @ Jul 12 2007, 10:45 PM) *
I might have missed too much of the discussion already, but here are some of my thoughts on the dead grandmothers:
  1. Brines moving up and down/disappearing: The obliquity on Mars changes much more severely and quickly than on Earth, due to not having a large moon. When the climate gets cold enough, the water in Meridiani froze out, then migrated to the poles, drying out the beds. When the climate warms up again, the returning water doesn't necessarily have the same composition as pre-ice age.
  2. Porosity of the rocks: The freezing at the end of each cycle drives the grains apart, preventing them from sealing shut.
  3. Distribution of the spherules + lack of solid masses of spherules: How well do we understand concretion creation (say that ten times fast!)? Do they require a "seed" at the center? If so, the seeds could be relatively uncommon, transported to Meridiani by wind, mixed with the sand/dust of the layers. Their relatively low abundance would not allow for large masses of concretions. The Navajo sandstone has another thing going for it: life! They've found life deep underground; the distribution of concretions in the sandstone could be modified by life in the rock, or in the original sand. See <a href="http://geology.utah.gov/online/pdf/pi-77.pdf" target="_blank">http://geology.utah.gov/online/pdf/pi-77.pdf</a>
  4. Not enough odd shapes (individual concretions): The shapes of the concretions are driven by the environment. I see no problem with more round concretions due to
    1. Lower gravity on Mars
    2. Lower depth of burial on Mars
    3. Porous rock
  5. Specular hematite: Sorry, my grandmother passed away. Can I get a pass? smile.gif
Did I miss any?


hendric - Thanks for your original thoughts. If none of them strike you as special pleading, perhaps you are a true believer. smile.gif As far as I'm aware, none of those aspects, especially those related to freezing (unthinkable if Meridiani was warm and wet), have ever been brought up by those proposing Meridiani concretions, so I don't feel particularly inspired to address them. The "life" aspect mainly serves a catalytic function - you still need brine flow and mixing to bring together the reactants in the oxidation reaction. All of the Utah-Arizona analogs are in pure quartz sandstones, insoluble, and of nearly uniform porosity and permeability - yet the nodular concretions (which consist predominantly of quartz grains, not reddish-brown hematite) behave extremely "badly" as described in prior posts. In rocks consisting of mystery dust and 30 % soluble salts, I would expect them to behave even more "badly" because the porosity and permeability of the rocks would be continuously altered (reduced) by salt recrystallization in the presence of the postulated all-salts-saturated brine, as also described in prior posts. But hey, Mars doesn't need to live up to my expectations, and you're allowed two dead grandmothers without challenge in my class (even if I don't need to believe you). The other one that you missed is the elevated Ni content. Now, just for insurance, better make an appointment for Grandpa's sex change operation... cool.gif

--HDP Don

Posted by: ngunn Jul 13 2007, 09:56 AM

Thanks for the reply, dburt. My doubts about the process have not been dispelled entirely though. On the other hand I am interested in the Nickel question. I wonder if we have anyone else here who could provide some expert comment on that?

Posted by: ngunn Jul 13 2007, 10:52 AM

On the convective updraught point - have you calculated the terminal velocity of these things in Martian air? My gut feeling is that it would be uncomfortably high in this context.

Posted by: centsworth_II Jul 13 2007, 02:51 PM

I have a hard time imagining the beads/berries forming high in a mushroom cloud
and then falling back to join the outward rushing ground surge. I would think that
the rapid evolution of the ground surge would be over by the time the more slowly
evolved beads had a chance to reach the ground. What am I missing?

Posted by: ngunn Jul 13 2007, 10:09 PM

Centsworth - since nobody else has come back on that point, yes, the relative timescales of the various processes that have to happen to emplace the berries in the Burt scenario is one aspect that is giving me problems when I try to 'run the simulation' in my head. Emotionally I like his ideas. I've always been uneasy about 'follow the water'. I'd prefer the science to be conducted under a directive like 'go and explore the universe and report what you find'. As a physicist I'm happier with bangs and things flying through the air than I am with subterranean chemical wizardry. Nevertheless this one is getting harder to believe the more I think about the details - and that's not good for any hypothesis.

Posted by: MarsIsImportant Jul 13 2007, 11:04 PM

Another major problem concerning an impact scenario is the geographic perspective. Is this one surge or many? If it is one, then the crater of origin should be traced. If that were the case, then we wouldn't be having this argument.

Regardless, the distribution of the hematite over Meridiani is a major problem. The signs suggest it is a more localized origin.

Posted by: dburt Jul 14 2007, 02:37 AM

QUOTE (ngunn @ Jul 13 2007, 03:09 PM) *
Centsworth - since nobody else has come back on that point, yes, the relative timescales of the various processes that have to happen to emplace the berries in the Burt scenario is one aspect that is giving me problems when I try to 'run the simulation' in my head. Emotionally I like his ideas. .... As a physicist I'm happier with bangs and things flying through the air than I am with subterranean chemical wizardry. Nevertheless this one is getting harder to believe the more I think about the details - and that's not good for any hypothesis.


ngunn and centsworth - Thanks for your comments. Unfortunately, I am not a physicist, nor an aerodynamic modeler, so if you find problems in the details of my made-up explanation, improve on them please. My starting point all along has been two facts:

1) Those berries, other than being round, just don't look like any actual concretions I've ever seen, not even the Utah-Arizona "Moqui marbles" that so much as been made of. Their near-perfect sphericity and size limitation makes them look much more like, say, hailstones.

2) My co-author Paul Knauth, when I was studying volcanic surge deposits in the 1970s, was himself studying some of the oldest rocks preserved on Earth (Archean Era), in South Africa. A puzzling feature of these rocks, in some sections, is 100's of square km of several-meters-thick spherule beds, preserved in marine sediments (meaning they have been water reworked, chemically altered, and flattened somewhat by the weight of overlying rock). These were initially thought to be volcanic accretionary lapilli, but their huge aerial extent and details of geochemistry (including Ni-enrichment) eventually convinced him and most other people who study them that they were related to meteorite impacts. Here is the link to the abstract of a 2003 summary article by Don Lowe in Astrobiology (full article accessible via a link), as cited in our 2005 Nature article (which has a photo of the spherules):

http://www.liebertonline.com/doi/abs/10.1089/153110703321632408

The full article reviews the historical controversies involved.

We're both Mars nuts from our earlier subsurface brine studies, and when the first web images came back from Opportunity in Eagle Crater showing the intricate pattern of cross-beds in sandy layers, I thought "surge" as a possiblity. At the same time, looking at the images on his own computer, Knauth thought "impact spherules" upon seeing the berries. We met for lunch that day and thus the hypothesis of "impact surge" was born - athough we initially called it "brine splat" to account for the salts. Shortly afterwards we invited Ken Wohletz of Los Alamos to join us, inasmuch as he knows far more about the nuts and bolts than we do. Naturally, we were both astounded by the complex "son of a beach" story, described as a scientific discovery, not merely a working hypothesis, that the MER team came up with a few weeks later - their story seemed so unlike the cold, dry Mars we knew, especially for the highlands, and ignored the impact craters all over the place.

Anyway, make up your own details, but the fact is that large terrestrial impacts (including the one that is presumed to have killed the dinosaurs, Chicxulub) produce, via vapor condensation processes, billions of spherules, comparable in sphericity and diameter to the berries at Meridiani, and scatter them at least as widely. Although terrestrial target rocks are much poorer in Fe than any on Mars, meaning the spherules are not particularly Fe-rich, the Fe in the spherules is invariably fully oxidized, and they are characteristically enriched in Ni (plus a whole suite of other elements that cannot be analyzed by the rovers). The Ni is usually concentrated in high temperature ferrite spinels, an end-member of which is the mineral trevorite, NiFe2O4 (Ni is 2+, Fe is 3+). No one yet knows how Ni occurs in the Ni-enriched Meridiani berries (Oppy's instrumentation is too primitive).

The MER team has argued that Oppy's berries can't be impact spherules, because terrestrial examples tend to be concentrated in distinct beds, but this argument ignores the obvious fact of concentration by faster settling velocities through seawater plus later current reworking (analogous the the obvious fact of wind-reworking for the lag concentration of berries on the surface of Meridiani).

So there you go - I really don't know exactly where in the vapor cloud they formed, or how long it took, or the details of how they were distributed, but the inescapable fact is that impact spherules characteristically happen, at least for ancient impacts on Earth (like Mars, a planet with atmosphere and subsurface volatiles).

Hope this admission of ignorance helps. smile.gif

HDP Don

P.S. Please note that for purposes of simplification I am using "impact spherules" in a very general and inclusive way that not all scientists would agree with (especially those who like to sub-classify everything). I am using it for all varieties of spherules resulting from vapor condensation after an impact (and excluding the splash droplets called tektites). Such condensates include direct condensates such as metals, glasses, minerals presumably including hematite, salts, brines, and liquid water or ice and snow. Some direct condensates, particularly brines, form sticky coatings on surfaces of other particles and tend to stick them together into spherical aggregates called accretionary lapilli. Accretionary lapilli and rare glassy microspherules can be produced by volcanism; the other varieties seem to require impacts (much more vaporization at a larger scale). Most impact spherules (direct condensates) are tiny and on Mars probably would be lost among the sand grains. Accretionary lapilli tend to be the largest impact spherules (or impact-related spherules, for the purist) and, as indicated in previous posts, that is what we hypothesize the hematitic spherules at Meridiani to be. Evidence, in addition to their relatively large size, includes the concentric structure seen in some broken ones, their sticky nature as indicated by occasional doublets and far rarer triplets, and doubts about their hematite content (somewhere in the range of 50-100%). The terrestrial impact spherules referred to above are mainly relatively large accretionary lapilli and other spherules believed to represent altered glass. Accretionary lapilli formed solely by terrestrial particulate matter plus condensing steam would not be expected to display an extraterrestrial trace element signature and, indeed, many don't (which is one reason why their impact origin has been controversial). Sorry for the technical lecture - I tend to oversimplify for this audience, and my co-author Knauth objected when he read the above post.

Posted by: dburt Jul 14 2007, 04:57 AM

QUOTE (MarsIsImportant @ Jul 12 2007, 11:01 AM) *
Geothite with hematite...it looks fairly Martian to me.

http://ocw.mit.edu/ans7870/12/12.108/f04/imagegallery/lab1/lab1-16.html

...very much like Meridiani, at least in a general sense.

MarsIsImportant - So which is the hematite, and which the goethite? Shiny, but where's the blue-gray color? I agree with you that those mineral surfaces are rounded, like those of the spheroids at Meridiani (and like those of concretions). There the resemblance ends. That is a typical photo of what a mineralogist calls "botryoidal growth" (sometimes called "mamillary growth" for a reason I won't specify) - basically meaning smooth rounded surfaces growing on a big lump. Many minerals, including both hematite and goethite, can grow that way. Concretions, including chert nodules in limestone, commonly grow that way, in nodular masses. Despite millions of spherules imaged, over 3 1/2 years, no such nodular lumps, or even hints of them, have ever been imaged by Oppy - that's only one of my criteria for stating they almost certainly aren't concretions. Helpful of you to provide the image. Thanks.

--HDP Don

Posted by: dburt Jul 14 2007, 07:35 AM

QUOTE (MarsIsImportant @ Jul 13 2007, 04:04 PM) *
Another major problem concerning an impact scenario is the geographic perspective. Is this one surge or many? If it is one, then the crater of origin should be traced. If that were the case, then we wouldn't be having this argument.

Regardless, the distribution of the hematite over Meridiani is a major problem. The signs suggest it is a more localized origin.

MarsIsImportant - Excellent suggestion. Three problems: 1) There are far too many candidate craters to choose from, 2) Oppy is nowhere near mobile enough to map a particular layer across all of Meridiani, to see if it got coarser in any particular direction, towards a particular parent crater. 3) If the parent impact crater or craters were in Meridiani itself, the exercise might be doomed from the start, because you would have only fine material to work with until you got right next to the impact target. Our present suspicion is that the surface of Meridiani Planum is probably covered my many relatively thin surge deposits resulting from late impacts within Meridiani itself. This process has possibly helped to homogenize the distribution of the hematitic spherules.

BTW, when you say "the signs suggest it is a more localized origin" what exactly do you mean? (Sorry to be so dense.) Thanks.

--HDP Don

Posted by: helvick Jul 14 2007, 07:46 AM

Ngunn - you asked about the terminal velocity of blueberries on Mars. For the current martian atmosphere (~12g/m^3) it would range from ~30 to ~50m/sec for fairly smooth spheres (Cd=0.5) composed of a material with a density of 5g/cc and diameter ranging for 2 to 6mm.

A surge cloud may be quite a bit denser than the current atmosphere and the atmosphere at the time probably bears little relation to the current one. In any case if you take a could density of 24g/m^3 those terminal velocities drop to ~20-35m/sec and a cloud density of 100g/m^3 yields velocities of ~10-17m/sec.

Posted by: MarsIsImportant Jul 14 2007, 07:49 AM

...Solution to many observational problems--HiRISE. Also, Triangulation is fairly easy.

Posted by: MarsIsImportant Jul 14 2007, 08:00 AM

QUOTE (dburt @ Jul 13 2007, 11:57 PM) *
MarsIsImportant - So which is the hematite, and which the goethite? Shiny, but where's the blue-gray color? I agree with you that those mineral surfaces are rounded, like those of the spheroids at Meridiani (and like those of concretions). There the resemblance ends. That is a typical photo of what a mineralogist calls "botryoidal growth" (sometimes called "mamillary growth" for a reason I won't specify) - basically meaning smooth rounded surfaces growing on a big lump. Many minerals, including both hematite and goethite, can grow that way. Concretions, including chert nodules in limestone, commonly grow that way, in nodular masses. Despite millions of spherules imaged, over 3 1/2 years, no such nodular lumps, or even hints of them, have ever been imaged by Oppy - that's only one of my criteria for stating they almost certainly aren't concretions. Helpful of you to provide the image. Thanks.

--HDP Don


I know all this already. You don't need to lecture me.

I simply brought this up because the article that you shot down suggested geothite could be a source for the hematite spherules...thinking outside the box.

Posted by: Shaka Jul 14 2007, 09:54 PM

Well, Science Marches On!
The Seventh International Conference on Mars, (held in Pasadena, not Mars smile.gif ) which concluded yesterday, involved a number of presentations directly referring to the "brine splat" hypothesis - not, generally, in a favorable light - Sorry, Prof Don. Perhaps most germane to this discussion is that of J.P. Grotzinger, "Depositional model for the Burns Formation, Meridiani Planum" http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3292.pdf
Perhaps you should take the paragraphs dealing with your impact hypothesis, and insert your rebuttles, as you did with the Squyres document. Of course some of the points have not changed.

Posted by: Bill Harris Jul 14 2007, 10:15 PM

Of course, we could hold the "First International Conference on the Brine Splat Belief" here at our own online Hyde Park... smile.gif and out do those duners.

--Bill

Posted by: ngunn Jul 14 2007, 11:21 PM

Helvick - thanks for those velocities. Dburt I'll try to be more specific about my misgivings. You yourself point out that each condensing species requires just the right physical and chemical parameters to form. You also mention that impact surges would be very turbulent. I have difficulty imagining that one of these particles, whatever trajectory it followed, would remain consistently in a suitable environment for superficial haematite accretion for long enough. Helvick's velocities suggest that at least in their later stages they are moving quite fast downward relative to whatever medium they are falling through. Another consequence of the turbulence, and the significant horizontal wind shear I would also expect, would be that particles from many different condensation environments should precipitate out in any given place. That's the haematite monoculture problem that I still don't think you have disposed of satisfactorily. Then there's the point Centsworth raised about any slow-forming spherules trapped (implausibly I feel) in quasi-stasis in a rising convective updraught above the hot crater simply arriving too late on the ground to be incorporated evenly through the the surge deposit.

And is it one or many haematite depositions we are looking at? A couple of us have asked but I don't recall a reply on that point.

You mention spherules associated with terrestrial impacts, which already answers the next question I was going to ask (well done!). I won't try to comment on that till I've looked into it.

You say you're not a physicist - well no-one can be everything - but I wonder if any of your collaborators have really worked through the mechanics (and timing) of the processes - properly, not just in my armchair fashion. You may have all the chemistry and mineralogy in place (or not, I wouldn't know) but the ballet cannot be performed unless the choreography also works.

Nickel: - a quick summary of the issues would be helpful if anyone has time.

Posted by: Kye Goodwin Jul 15 2007, 04:36 AM

nqunn, Dr Burt, I have a question about the nickel enrichment of the spherules. One of the Dec 04 Science articles (R Rieder, R Gellert et al.) summarizes the APXS results from Eagle Crater. Berry Bowl Full was the only spherule target. It had nickel levels about 30% higher than the average of about a dozen rock targets in Eagle Crater and 10% higher than the next highest. The soil targets are a lot more variable in Ni than the rock targets and one Jack Russel (surface) shows Ni about 15% higher than the sole spherule target. If this is the only data it doesn't seem strong enough to hang a lot on, more like a preliminary indication that the spherules might be Ni-enriched. It would be nice to have a few more spherule targets.

Is there any more data on Ni enrichment of spherules from later in the mission?

Posted by: tty Jul 15 2007, 07:03 PM

There are some things that I find problematic with the impact spherule hypothesis

1. Impact spherules while predominantly spherical usually contain a fair proportion of "oddballs", for example dumbbell and teardrop shapes. These are absent in Meridiani.

2. The spherules are all near the extreme maximum size ever seen in terran spherule deposits. On Earth these very large spherules have only been found quite close to impact craters and seem to be rare even there. Also I'm unaware of any deposit on Earth that consists exclusively of such large sperules.

Posted by: nprev Jul 16 2007, 03:12 AM

Please forgive the generalism, but this may be a useful context question: How unique is Meridiani in terms of its geology?

I have been visualizing the area as a sort of Yellowstone Park of Mars in terms of its distinction from most of the surrounding terrain (only an analogy, of course, not trying to imply hydrothermal influences here!) IIRC, MGS data revealed very few hematite-rich areas, and none as extensive as those in Meridiani.

What I'm getting at here is that the berries may indeed be a product of unique, site-specific processes. The Gusev lapilli observed do not seem to be comparable in origin or morphology (except in the most gross perspective) to Meridian's berries. Therefore, it may not be useful to consider similar formation mechanisms, save in the most coarse particulars (i.e., presence of water).

This viewpoint weakly supports HDP Don's hypothesis, but any confirmation would, IMHO, require discovery of very similar geology elsewhere on the planet...a real dice-throw when we're talking current UMSF capabilities. We only get precious peeks of ground truth, demonstrably not yet enough to tell a coherent story.

Posted by: ngunn Jul 16 2007, 08:07 AM

QUOTE (nprev @ Jul 16 2007, 04:12 AM) *
How unique is Meridiani in terms of its geology?


There is a recent paper describing Meridiani as the area of convergence, and emergence, for groundwaters flowing laterally out of raised water tables under the higher ground to the south and west. It's been linked here somewhere - I even printed it out. Unfortunately my filing system is almost as unfathomable as the geological history of Mars.

Posted by: ngunn Jul 16 2007, 02:18 PM

It had it's own thread, though not many posts surprisingly:

Under Opportunity, 'Meridiani Planum . . .' started by Alex Blackwell.
http://www.unmannedspaceflight.com/index.php?showtopic=3999
http://www.space.com/scienceastronomy/070307_mars_evaporite.html

I notice the free access to the full paper is no longer available. Pity, it had nice diagrams.

Posted by: don Jul 16 2007, 08:05 PM

Dburt

From day one the principal shortcoming of the impact surge model IMO was the look of the sediments examined, they just never really looked like impact debris as described for terrestrial impacts. They look just a little too neat and orderly. Granted paper after paper describes a spherule layer associated with Chicxulub impact debris the likeness stops there. It’s difficult to imagine melt globules or tektites going through deceleration and atmospheric compression to have the pristine look of the meridiani spheres. The presence of the spheres within cross bedded units imply formation within an energetic cloud not a gentle distal depositional rain as has been suggested for the surge model.

I guess we were extremely lucky to find distal ejecta layered on top of distal ejecta at meridiani. Odds are we would find proximal ejecta also spread across the plains of meridiani if we are talking about multiple impacts, so where is the diamictite, the coarse ejecta, target rock clasts? Chicxulub impact debris (I’ll ignore Gerta Keller for now) has been well documented and it doesn’t look anything like meridiani sediments. The likelihood of the demolition derby model of impact after impact eventually grinding down any ejecta on mars to a fine-coarse sand is dubious at best.

A comment in a July 15 Space.com article - It's fairly dark rock,'' Jirsa said. "They look like concrete, but in this concrete you would throw pieces of rock of all sizes and shapes and in all possible orientations.'' This was said of a possible discovery of Sudbury meteor impact debris in Minnesota. Now that’s impact debris !!

"the other don"

Posted by: dburt Jul 16 2007, 10:42 PM

QUOTE (Shaka @ Jul 14 2007, 02:54 PM) *
Well, Science Marches On!
The Seventh International Conference on Mars, (held in Pasadena, not Mars smile.gif ) which concluded yesterday, involved a number of presentations directly referring to the "brine splat" hypothesis - not, generally, in a favorable light - Sorry, Prof Don. Perhaps most germane to this discussion is that of J.P. Grotzinger, "Depositional model for the Burns Formation, Meridiani Planum" http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3292.pdf
Perhaps you should take the paragraphs dealing with your impact hypothesis, and insert your rebuttles, as you did with the Squyres document. Of course some of the points have not changed.


Shaka - Umm, well, golly, just what did you expect all those HDPs to say? The same question has also been raised with regard to the same abstract 3292, in a general way, in Post 184 from July 10, and answered, likewise in a general way, in my post 194 on the same date (and also in many other posts). As you correctly noted, most of the objections raised by the HDPs in question were already shot down more than a year earlier in our point-by-point rebuttals to their unpublished Nature criticism. Nature declined to publish it after their editor and two external reviewers had evaluated both their claims and our rebuttals. See the attachment to my post 170 of July 9. So if you would like me to evaluate a specific claim, please specify which one, or else I'll just be repeating myself more and more and more...

BTW, I suggest you look closely at Figure 3 of that extended meeting abstract 3292 and compare it with, say, Figure 5 of the following field trip guide:
http://www.gps.caltech.edu/~carltape/personal/images/ge136/NavajoB.pdf

You will see that, rather than being an original interpretion based on exposed Burns Cliff geology, it is basically a repeat of what has been the standard story for the Navajo Sandstone for many, many years, applied almost without change to Mars (ignoring the distinctly non-dune aspect of virtually all of the bedding, the 30% sulfate salt content, and most other features, including the unexplained huge gouge taken out of the left side of the single large cross-bed that was alleged to be an old water table). The Navajo and Page Sandstones, type examples for so-called "Stokes surfaces" or old water tables, consist almost entirely of equigranular pure quartz sand (insoluble) and are essentially salt-free. The interdune playas in them were true desert oases with shales containing muddy dinosaur footprints and somewhat palm-like trees called cycadoids growing there too (flowering plants like true palms hadn't evolved yet). I.e., distinctly not salty, with clear geologic indications of standing water. Read the above on-line guidebook for more details. There are no associated signs of flowing water (e.g., no alleged "festoons") at all in the Navajo, as far as I am aware and, as mentioned in several previous posts, the clumped-together to massive-nodular hematitic concretions in it and the overlying Page Sandstone are commonly concentrated at or just below the old water tables - not uniformly in the rock.

BTW, as mentioned in Post 194, I consider it a major advance that HDP Grotzinger has finally admitted that his 2005 "Navajo Sandstone on Mars" hypothesis is actually just a model rather than a discovery, and that he has given our impact ideas some exposure by explicitly attacking them. In science as in life you have to take what little you can get. smile.gif

--HDP Don

Posted by: dburt Jul 16 2007, 11:02 PM

QUOTE (centsworth_II @ Jul 13 2007, 07:51 AM) *
I have a hard time imagining the beads/berries forming high in a mushroom cloud
and then falling back to join the outward rushing ground surge. I would think that
the rapid evolution of the ground surge would be over by the time the more slowly
evolved beads had a chance to reach the ground. What am I missing?


Centsworth - I'm not asking you to imagine anything you don't want to, and you're not missing anything. As mentioned in previous posts, several different surge types conceivably might result from the same large impact - 1) an initial blast surge along the ground, like those imaged related to atom bomb testing in the Nevada desert, 2) a column-collapse type surge cloud containing the berries, analogous to a pyroclastic flow in volcanology (or an Arizona dust storm resulting from thunderhead collapse), 3) local phreatomagmatic type surges resulting from impact melt in the crater reacting explosively with melted ice or other groundwater (analogous to what the MER team has suggested for Home Plate in terms of a vanished volcano). This latter type mechanism is what Wohletz and Sheridan (1983) suggested for the formation of classic "rampart craters" on Mars. By whatever mechanism, the fact is that very similar (except for composition), considerably larger accretionary lapilli have formed in terrestrial impacts, and were more widely distributed in South Africa and Australia than the ones at Meridiani. Also, as mentioned in previous posts, even if you were to dump the hematitic spherules all in the same place next to a crater, it probably wouldn't matter, because later impact surges could scour and scatter them across the entirety of Meridiani Planum, and they would be embedded in the resulting cross-bedded sandy rock. Good question.

--HDP Don

Posted by: dburt Jul 16 2007, 11:19 PM

QUOTE (helvick @ Jul 14 2007, 12:46 AM) *
Ngunn - you asked about the terminal velocity of blueberries on Mars. For the current martian atmosphere (~12g/m^3) it would range from ~30 to ~50m/sec for fairly smooth spheres (Cd=0.5) composed of a material with a density of 5g/cc and diameter ranging for 2 to 6mm.

A surge cloud may be quite a bit denser than the current atmosphere and the atmosphere at the time probably bears little relation to the current one. In any case if you take a could density of 24g/m^3 those terminal velocities drop to ~20-35m/sec and a cloud density of 100g/m^3 yields velocities of ~10-17m/sec.


Helvick - So what is the terminal velocity of a golfball- or tennisball-sized hailstone on Earth? They're not very common, but when they do occur, they can be an absolute nightmare for insurance companies, because they can take out the windshields of every ungaraged automobile in a town. And those form in normal thunderstorms, with no dense material (such as hematite nano-flakes of specific gravity of 5.26) contained in the upwelling clouds, and with energies many orders of magnitude less than those implicit in a decent-sized impact.

BTW, I like the way you are taking our argument - that the 5 mm size maximum for the berries might indicate the maximum size that can be supported in an upwelling impact cloud on Mars - and trying to turn it around to bite us. Good debating technique (verbal ju-jitsu). However, keep in mind that the specific gravity of the berries might be considerably less than that of pure hematite (5.26) if they contain other constitutents or were originally accreted loosely, with original porosity. Finally, you might want to share the equations, or at least assumptions and constants, that you are using in your calculations.

--HDP Don

Posted by: dburt Jul 16 2007, 11:28 PM

QUOTE (MarsIsImportant @ Jul 14 2007, 01:00 AM) *
I simply brought this up because the article that you shot down suggested geothite could be a source for the hematite spherules...thinking outside the box.


Umm - Goethite as a precursor for hematite was studied by Glotch when Meridiani hematite was thought to result from 300 C metamorphism of a sedimentary iron formation. He was merely trying to find evidence in favor of a now-discarded hypothesis. However laudable that goal, I'd hardly call it "thinking outside the box." Of course, I may be fussy that way. biggrin.gif

--HDP Don

Posted by: dburt Jul 17 2007, 12:35 AM

QUOTE (ngunn @ Jul 14 2007, 04:21 PM) *
Helvick - thanks for those velocities. Dburt I'll try to be more specific about my misgivings. You yourself point out that each condensing species requires just the right physical and chemical parameters to form. You also mention that impact surges would be very turbulent. I have difficulty imagining that one of these particles, whatever trajectory it followed, would remain consistently in a suitable environment for superficial haematite accretion for long enough. Helvick's velocities suggest that at least in their later stages they are moving quite fast downward relative to whatever medium they are falling through. Another consequence of the turbulence, and the significant horizontal wind shear I would also expect, would be that particles from many different condensation environments should precipitate out in any given place. That's the haematite monoculture problem that I still don't think you have disposed of satisfactorily. Then there's the point Centsworth raised about any slow-forming spherules trapped (implausibly I feel) in quasi-stasis in a rising convective updraught above the hot crater simply arriving too late on the ground to be incorporated evenly through the the surge deposit.

And is it one or many haematite depositions we are looking at? A couple of us have asked but I don't recall a reply on that point.

You mention spherules associated with terrestrial impacts, which already answers the next question I was going to ask (well done!). I won't try to comment on that till I've looked into it.

You say you're not a physicist - well no-one can be everything - but I wonder if any of your collaborators have really worked through the mechanics (and timing) of the processes - properly, not just in my armchair fashion. You may have all the chemistry and mineralogy in place (or not, I wouldn't know) but the ballet cannot be performed unless the choreography also works.

Nickel: - a quick summary of the issues would be helpful if anyone has time.

ngunn - Good questions. I myself have trouble imagining how golfball-sized hailstones form on Earth, but they do, and for a Mars impact we have many, many orders of magnitude more energy available, with much less gravitational force. For Meridiani spherules, the environment(s) of formation is/are probably not the same as the environment(s) of distribution, and there can be as many periods of surge distribution as there are impacts, if the spherules initially were concentrated on the surface or in easily eroded rocks (mentioned in previous posts). Or several surges are possible per impact, as also mentioned. As to where other types of spherules related to vapor condensation might be, in previous posts I have hypothesized that either 1) they were soluble in late-condensing steam and therefore ephemeral, as most fumarolic condensates related to volcanism are or 2) if insoluble, they are too small to be distinguished from far more abundant sand grains (typical impact spherules, such as the iron condensation spherules that surround Meteor Crater, AZ, are very tiny). Keep in mind that the observational tools of Oppy are incredibly primitive by any terrestrial laboratory standard, however revolutionary they may be in terms of prior Mars exploration.

You can have as many spherule depositional episodes as you want, but one would suffice for Meridiani, I think.

If you want a separate Ni discussion from me - ask for one (although much of it would be a summary of material already posted). My impression is that you'd like one from someone else?

Keep in mind that no matter how defensive or ineffectual I've been in explaining it here, the "impact surge" hypothesis is just one of three out there for Meridiani alone (let alone for Gusev or the rest of Mars). I'm just trying to make this group well-informed consumers of science. You all get to decide whom to believe for yourselves.

And hey, if I could do all the choreography, I wouldn't be sitting here typing this - I'd be a God. biggrin.gif

--HDP Don

Posted by: dburt Jul 17 2007, 01:48 AM

In early March 2004, about a month after Oppy landed, ASU experienced a severe hail storm around dusk like none it has experienced before or since. I managed to snap these photos before all the ice melted (bricks give scale):





You might call this a "Eureka moment" regarding the blueberries. Enjoy, and that's all for today.

--HDP Don

P.S. As I write this I'm getting a nice view out of my south-facing 6th floor window of a distant ground-hugging dust storm advancing across the plains south of Phoenix It presumably resulted from column collapse in a thunderstorm in the hills to the east. Such dense, cold air currents commonly knock over construction fences or trailer homes, but are real wimps compared to a volcanic surge, let alone an impact surge.

Posted by: CosmicRocker Jul 17 2007, 05:33 AM

QUOTE (don @ Jul 16 2007, 03:05 PM) *
I guess we were extremely lucky to find distal ejecta layered on top of distal ejecta at meridiani. ...
"the other don"
O'don: That's one of the things that bothers me most about multiple impact scenarios. As for the observed size distributions of various berry populations, all kinds of hypotheses can be erected to match those. I'm not certain any of them lead us to a confident conclusion. It seems that Fe diffusion below a slowly changing water table matches the data as well as other models.

Posted by: Shaka Jul 17 2007, 06:42 AM

QUOTE (dburt @ Jul 16 2007, 03:48 PM) *
...snip... but are real wimps compared to a volcanic surge, let alone an impact surge.

Really, Don, that is the bottom line for me. Ever since Eagle crater I've been looking at this 'rock', and I just cannot believe that it is the result of the incomprehensible violence of impacts.
I stand in awe of impacts. I am convinced that they are the ultimate drivers of the macroevolution of earth's biology, and that all global mass extinctions, as well as many regional catastrophes, are their outcomes.

Where is that violence in the Meridiani evaporites? Where is the chaos? Where is the crushed matter?
You ask what at Meridiani cannot be explained by impact surge. I say "its totality".
Cheers,
Shaka

Posted by: MarsIsImportant Jul 17 2007, 07:24 AM

That's the point, isn't it? A volcanic surge or impact surge is Not the same thing as a hail storm--even though they might have a few similarities.

By the way, I've been through a lot bigger hail storms. Some of them covered the ground completely with 4 to 5 inches of hail. In a couple of instances, it was quite an experience--possibly life threatening if I had not found adequate cover for safety. And I do understand golf ball sized hail. It's the grapefruit sized and larger that are difficult to understand, although somewhat easy to explain.

Posted by: ngunn Jul 17 2007, 10:10 AM

QUOTE (dburt @ Jul 17 2007, 01:35 AM) *
You can have as many spherule depositional episodes as you want

if I could do all the choreography, I wouldn't be sitting here typing this biggrin.gif

--HDP Don


Thanks again for your reply. I do appreciate that nobody has explanations yet for all the details, but whereas the 'official' model has billions of years to work its tricks your scenario has to do it in, say, half an hour. I think that makes having a convincing model for the choreography vital to the credibility of the case you're making. At the moment you leave a lot of important parameters in soft focus, so it's not surprising that some people express a 'vague sense of unease' in response.

For a while I thought the nickel clue might be a piece of hard evidence one way or another, but I'm beginning to doubt that now. I did read what you said about it in your paper, but it doesn't seem like very strong evidence there. Likewise the rebuttal by Squyers et al., saying that the nickel isn't enriched enough for the iron to be meteoritic simply begs the question of what mix of meteorite and target rock would have gone to form the spherules - another enormous free parameter in your scenario. Yes I was hoping others would chime in but perhaps nobody sees much mileage in it.

Posted by: don Jul 17 2007, 01:27 PM

CosmicRocker

Fe diffusion in some form makes sense. Why would Grotzinger lead us astray? rolleyes.gif As I’ve stated before, the proposed surge deposits don’t resemble anything we have here on good ol’ earth. The hallmark or fingerprint of a large impact on earth is chaotic rubble - diamictite beds on a grand scale and shock metamorphism on a micro scale. Obviously the micro-scale isn’t available to us with MER but the large scale evidence should be. Burt and Knauth try to keep the debate to the small scale where Grotzinger et al are vulnerable; raising a red flag is relatively easy at that scale. Look at Chicxulub ejects beds and then meridiani sediments, you won’t see many similarities, yet we should if multiple ejecta beds are ubiquitous at meridiani.

Don’t get me wrong Burt et al have been the greatest thing to happen to the MER team in terms of keeping people on their toes and looking over their shoulder for the latest volley from ASU. The surge model did get some unconstructive recognition at the recent Seventh Int Conf on Mars but I’m sure even that was encouraging for its supporters.

Posted by: helvick Jul 17 2007, 02:52 PM

QUOTE (dburt @ Jul 17 2007, 12:19 AM) *
Helvick - So what is the terminal velocity of a golfball- or tennisball-sized hailstone on Earth?
....Finally, you might want to share the equations, or at least assumptions and constants, that you are using in your calculations.

Hmmh you may have found that I made a fairly basic error in my calculations. Seems I worked out terminal velocities for 0.5mm spherules. If so then good catch, if not well it is clearly a good idea to ask for things to be worked out openly. Anyway to answer the questions and rework the hematite spherule calculation.

Some anecdotal web research http://www.blueprintforsafety.org/hail/hdamage.aspx.

Let's see if that makes sense.

My calculations for this us the following values; Coefficient of drag = 0.4, Density of (terrestrial air) = 1.2kg / m^3 and Density of Hail = 900kg/m^3.
Using the following formulae:
Drag Force : Fd=(1/2)*Cd*rho*A*v^2 , where Cd=Coefficient of Drag, rho=density of the medium (atmosphere), A=cross sectional area of the object and v=velocity
Force due to gravity : Fg= g*M where g = local gravity and M = Mass of the object.

At terminal velocity by definition both of the above must be equal so:

Vt=sqrt ( 2*Mass*g / (Cd*rho*A) ).

This obviously assumes simple fluid dynamics ie relatively slow velocities with no shock waves\subsonic etc. Also the coefficient of drag could vary quite a bit but it's not going to be significantly far from 0.4 for objects that are fairly smooth spheres.

Anyway these terrestrial values yield the following for hailstones:
Tennisball (6.7cm) - 40.5m/sec (91mph)
Golfball (4.27 cm) - 32.3m/sec


For comparison the same items on Mars (12g/m^3 atmospheric density and 3.822m/s^2 gravity) give
Tennisball - 260 m/sec (584mph)
Golfball - 207 m/sec


And so on to my earlier error. Hematite (well something with a density of 3g/cc) spherule. Taking Cd=0.4 because I don't have any better number and using 12g/m^3 for atmospheric density, 3.822 for g.
5mm diameter - 126m/sec (284 mph)
On Earth it would be 20m/sec (45mph)


Apologies again for the errors in the earlier calculations. I don't know whether the change actually skews things in favour of the hypothesis or not. What it certainly would account for is the absence of large concretions - a tennisball sized hematite spherule with a density of 3g/cc has a terminal velocity of about 400m/sec.
QUOTE (dburt @ Jul 17 2007, 12:19 AM) *
...and trying to turn it around to bite us. Good debating technique (verbal ju-jitsu).

That wasn't my intention (Honest!), I think that the hailstone-style formation model in an impact surge column\collapse seems like the easiest way to get the physical attributes the way they are. I'm just trying to see if the numbers that I'm able to hack together make it seem more or less likely. I haven't figured out which way it's leaning yet myself but I've got to admit I'd like to see it be possible - hematite hail has a nice ring to it.

Posted by: Aussie Jul 17 2007, 11:01 PM

Dburt
If I understand correctly you are proposing that that the spherules are hematite microkrystites that condensed out of the impact plume and then distributed through an extremely thick surge deposit rather than as a boundary layer. This stretches my imagination to a degree and there does not seem to be any evidence of tektites coincident with the microkrystites, or any evidence of splash forms or other melt products. The apparent thickness of the spherule rich layer does not fit a single impact layer scenario and the fact that the hematite rich area of Mars is limited to Meridiani indicates that hematite microkrystites are not a feature of impacts on Mars, or indeed to the best of my knowledge do they have a hematite analogue in Earth impact surge deposits. Or am I missing something?

Posted by: helvick Jul 18 2007, 12:19 AM

One other interesting thing about the potential terminal velocity of the spherules is that as the size approaches 16mm in diameter the terminal velocity approaches Mach 1 at ground level (~223m/sec). Mach 1 at 50km on mars is around 180m/sec which would correspond to a spherule diameter of 10mm.

I'm not really sure if this is going anywhere but it seems to me that it would be highly unlikely that anything could form smoothly in the transonic regions so that there would be a hard limit somewhere between 5 and 20mm diameter for fairly dense (>3g/cc) accretionary spheres forming in either a vertical plume or laterally travelling surge on mars that approximated the density of the current martian atmosphere. That latter assumption seems unlikely to me though.

I'm wondering how one would go about modelling the dynamics of an impact's plume to try and explore what sort of vertical velocity\pressure\temperature profile would be seen post impact. I can imagine scenarios that would allow accretions to grow to a limit and eventually rain out as they get too big to continue to rise but I've no idea if they can actually happen.

Posted by: Shaka Jul 18 2007, 12:57 AM

Hydrocode modelling of impact plumes is an ongoing industry in Arizona (Google Scholar the publications of HJ Melosh, E Pierazzo, BA Ivanov, NA Artemieva), but microtektites are mainly seen as the condensation products of vaporized rocks in the distal ejecta of large impacts. I have not seen in the models the scenario of "hailstones" falling out of a horizontal surge cloud as they grow to a certain size. That doesn't say it's impossible, just that it doesn't seem to figure large in the models. The horizontal surges really contribute mostly to the proximal ejecta, forming the chaotic meter-scale clastic deposits such as those that surround Chicxulub in Mexico, Belize, Cuba, Texas etc.

Posted by: dburt Jul 18 2007, 01:13 AM

QUOTE (Kye Goodwin @ Jul 14 2007, 09:36 PM) *
nqunn, Dr Burt, I have a question about the nickel enrichment of the spherules. One of the Dec 04 Science articles (R Rieder, R Gellert et al.) summarizes the APXS results from Eagle Crater. Berry Bowl Full was the only spherule target. It had nickel levels about 30% higher than the average of about a dozen rock targets in Eagle Crater and 10% higher than the next highest. The soil targets are a lot more variable in Ni than the rock targets and one Jack Russel (surface) shows Ni about 15% higher than the sole spherule target. If this is the only data it doesn't seem strong enough to hang a lot on, more like a preliminary indication that the spherules might be Ni-enriched. It would be nice to have a few more spherule targets.

Is there any more data on Ni enrichment of spherules from later in the mission?

Kye - More data was contained in a July, 2005 Nature paper on soils by Yen et al. - they pointed out (via a graph) that Fe was positively correlated with Ni in the Berry Bowl experiment - suggesting an enrichment in Ni in the berries. That all Meridiani rocks appear to be somewhat enriched in Ni (for unknown reasons) - adding possible support for an Fe,Ni-sulfide target or a Ni-rich impactor - was published by Yen et al. in JGR in 2006.

The most recent Ni discussion, by McLennan et al., is here:
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3231.pdf
This abstract, of course, misquotes our 2005 Nature article as implying that the Fe/Ni ratio in the berries must match that of an Fe,Ni meteorite and seemingly implies that the late Roger Burns (after whom the Burn Formation was named) was a complete fool for inferring that Fe,Ni sulfide deposits should be common on Mars. It compares the Ni/Fe ratio in the spherules with that in the rocks as a whole, clearly comparing apples to oranges, inasmuch as all of the Fe is presumably oxidized (3+) and the Ni is reduced (2+). It should instead have considered the Mg2+ content of the host rocks - that is where the Ni2+ would partition, if the rocks were ever soaked in a brine (really elementary crystal chemistry.)

In this regard, its second page states "At least four distinct groundwater (brine) recharge events...can be documented or inferred..." whereas its last page states "Nevertheless, the general textural integrity of the Burns formation suggests that the amount of fluid that has interacted with these rocks after deposition of diagenetic cements has likely been very small (Fig. 3)." Now if that isn't having your cake (soaking the wind-transported salts in multiple brines) and eating it too (maintaining textural integrity), I don't know what is, as I have brought up in many previous posts. Fig. 3 shows the drastically different solubilities of gypsum vs. some other salts (except jarosite, which was left off). This graph, BTW, provides a strong argument against the extant playa model - if there were a vanished playa with the wind blowing across it, gypsum-only dunes should have been produced, as in ALL terrestrial examples, while the far more soluble salts soaked into the mud or disappeared underground (or at least, stayed too damp for the wind to move).

The assertion that Ni2+ substituted in crystalline hematite (for Fe3+) via addition of a proton (H+) to provide charge balance, seems dubious too, but is technical enough that it probably deserves a separate discussion. (About as probable as a 4-foot tall wanna-be basketball player being allowed to join a championship-bound team of 6-footers because he is standing on the shoulders of a 2-foot tall "little person".)

The bottom line is that I can conceive of no reason why low temperature concretionary hematite, soaked in acid brine in the presence of abundant Mg-phases, should be enriched in Ni, even by adsorption. The Ni2+ should stay with the Mg2+ in the host rocks (as Mg-sulfates, Mg-clays, etc.) which has the same ionic size and charge, and does so in every terrestrial example with which I am familiar.

Incidentally, some adsorption of Ni into hematitic concretions is reported by Beitler et al. (2005) "Fingerprints of fluid flow..." for the Navajo Sandstone here:
http://jsedres.sepmonline.org/cgi/content/abstract/75/4/547
but that was a system without Mg-phases (i.e., the hematite had no competition for Ni) and was possible only because of the alkaline pH (see the calculated adsorption curves in their Fig. 9B). If you are able to look up that article, check out their Fig. 3 for examples of what the spherule and color distribution at Meridiani might look like if fluid flow and brine mixing had indeed been responsible (especially Fig. 3E).

A useful quote (p. 550-551): "Small concretions commonly coalesce to form larger clumped concretions (Fig. 3E, F). Concretionary iron oxides occur in a variety of morphologies including tabular subvertical mineralization filling joints or faults, vertical pipes, subhorizontal planar strata-bound pipes, tubes, sheets, and/or irregular bodies, Liesegang-type banding, and regional zones of organized spherical concretions (Chan et al. 2000, Chan et al., 2004). These range in color from dusky brown to dusky red..." Couldn't have said it better myself. smile.gif

Speaking of berries, a recent summary of the hematite content of the berries by Joliff et al. (2007) is here:
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3374.pdf
This abstract concludes, after considerably hemming and hawing about coatings, dust, and other factors, that the spherules probably are not pure hematite, but leaves a very wide range of compositions open.

Another spherule abstract by Calvin et al. (2007) is here:
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3163.pdf
Predictably, it uses the same arguments I use to argue against their being concretions (size and shape, lack of any evident pathway controls, lack of clumping, etc.) to argue that they are concretions. Go figure. The blue-gray color issue is never addressed. At least I was pleased to see that the above two abstracts referred to the berries as "spherules" rather than "concretions". Little by little...

--HDP Don

Posted by: dburt Jul 18 2007, 01:41 AM

QUOTE (tty @ Jul 15 2007, 12:03 PM) *
There are some things that I find problematic with the impact spherule hypothesis

1. Impact spherules while predominantly spherical usually contain a fair proportion of "oddballs", for example dumbbell and teardrop shapes. These are absent in Meridiani.

2. The spherules are all near the extreme maximum size ever seen in terran spherule deposits. On Earth these very large spherules have only been found quite close to impact craters and seem to be rare even there. Also I'm unaware of any deposit on Earth that consists exclusively of such large sperules.

tty - Thanks for your questions. I may already have answered them in previous posts (especially the postscript to #245), but impact accretionary lapilli are exclusively spherical, as far as I am aware. "Impact spherules" narrowly defined include glass condensates which could take on odd shapes before they congeal. However, even those should not be confused with very irregular to teardrop-shaped tektites - glassy splash droplets of impact melt.

If you think 5 mm is close to the maximum size ever seen in terran spherule deposit, I disagree, unless you are leaving out spherical impact accretionary lapilli, which is what we believe the Meridiani hematite spherules to be (impact spherules, sensu strictu, are direct condensates and are smaller). Also, 5 mm is only the maximum size seen for Meridiani spherules - most are smaller to much smaller.

Hope that helps.

--HDP Don

Posted by: dburt Jul 18 2007, 01:50 AM

QUOTE (ngunn @ Jul 16 2007, 01:07 AM) *
There is a recent paper describing Meridiani as the area of convergence, and emergence, for groundwaters flowing laterally out of raised water tables under the higher ground to the south and west.

That paper was not geology as usually understood. It was a hydrological inferrence used solely to justify, completely after the fact, the MER team's "invisible playa" or "lost oasis" or "Navajo Sandstone on Mars" hypothesis for Meridiani. The only unique feature of Meridiani geology as seen from orbit was the huge aerial extent of the specular (blue-gray) hematite signature. Finely layered, probably sulfate-rich sediments occur in many, many other areas around the highlands, as first noted by Malin and Edgett (2000, Science).

--HDP Don

Posted by: dburt Jul 18 2007, 02:07 AM

QUOTE (don @ Jul 16 2007, 01:05 PM) *
Dburt

From day one the principal shortcoming of the impact surge model IMO was the look of the sediments examined, they just never really looked like impact debris as described for terrestrial impacts. They look just a little too neat and orderly. Granted paper after paper describes a spherule layer associated with Chicxulub impact debris the likeness stops there. It’s difficult to imagine melt globules or tektites going through deceleration and atmospheric compression to have the pristine look of the meridiani spheres. The presence of the spheres within cross bedded units imply formation within an energetic cloud not a gentle distal depositional rain as has been suggested for the surge model.

I guess we were extremely lucky to find distal ejecta layered on top of distal ejecta at meridiani. Odds are we would find proximal ejecta also spread across the plains of meridiani if we are talking about multiple impacts, so where is the diamictite, the coarse ejecta, target rock clasts? Chicxulub impact debris (I’ll ignore Gerta Keller for now) has been well documented and it doesn’t look anything like meridiani sediments. The likelihood of the demolition derby model of impact after impact eventually grinding down any ejecta on mars to a fine-coarse sand is dubious at best.

A comment in a July 15 Space.com article - It's fairly dark rock,'' Jirsa said. "They look like concrete, but in this concrete you would throw pieces of rock of all sizes and shapes and in all possible orientations.'' This was said of a possible discovery of Sudbury meteor impact debris in Minnesota. Now that’s impact debris !!

"the other don"


Other Don - Well, got your terrestrial blinders firmly fastened still? This applies to impacts too. This question was first asked by Shaka in his post #56 and answered by me in post #60, as well as in later posts. Two factors you possibly haven't considered: 1) Earth has had solid bedrock for impact targets, owing to plate tectonic processes, shallow marine sedimentology, and so on. On Mars at the end of the Late Heavy Bombardment and prior to most Tharsis volcanism, solid bedrock may have been a commodity in rather short supply. As I said in prior posts (as per Wm. K. Hartmann's "kablooey of dust and steam" quote), beat on Meridiani, and you'll just get more Meridiani. 2) Terrestrial impact studies are highly biased by the immediate removal and alteration of distant fines, such as those we see at Meridiani. They simply aren't available for study on Earth. That doesn't mean they were never there. Volcanic surges tend to be preserved by overlying lava flows or ignimbrites. No such luck for impact surges - you mainly preserve the coarse breccia (suevite) near the crater, or spherules in marine sediments. And I'm getting tired of repeating this - we never claimed that the Meridiani spherules were "melt droplets or tektites" - they appear to be impact accretionary lapilli of unusual composition.

--HDP Don

P.S. (added a day later). Last night I forgot to mention two other reasons, other than possible rarity of bedrock targets and likelihood of erosion/alteration, why impact processes on Mars are probably different from those on Earth (so please remove your terrestrial blinders). The first is that the Martian subsurface is frozen, probably to a depth of several kilometers (the so-called cryosphere), and probably has been since at least the end of the Late Heavy Bombardment (because erosional remnants of very old rampart craters are found, and these are widely accepted as evidence of the martian cryosphere). A cold, brittle, broken impact target, with up to several tens of percent ice (permafrost) cementing it, is probably going to break far more violently as its ice flashes into steam, than any terrestrial bedrock target. Therefore, many more fine particles will be produced. In this regard, so-called rampart craters appear unique to Mars, and are themselves probably preserved only as erosional remants (coarser and/or better cemented, near-crater materials).

The second, as mentioned in previous posts, is that the surface of Mars (unlike that of Earth) has probably always been covered nearly everywhere with a thin to thick veneer of drifting sand and dust (most of it probably impact-derived), because there usually is no liquid water to cement it into a rock (although ice cements it at the poles). An impact surge cloud will scour and transport all that sand and dust and incorporate it into the steam- and salt-cemented surge deposit - which therefore is going to look extremely sandy, compared to most terrestrial surge deposits (volcanic or impact). In an earlier post I already used this feature as an argument for why the sandy surge deposits at Home Plate are probably impact- rather than local volcano-related, despite their single ballistic sag. It may also help explain the sandy nature of the Meridiani deposits (along with simple impact reworking of earlier sandy layered deposits, mentioned in my original post).

Hope that helps remove the blinders. BTW, without mentioning names, some people who study terrestrial and lunar impacts have been EXTREMELY opposed to the idea that the Meridiani deposits could be impact related. Your reaction (and the original one of Shaka) have been comparatively mild. smile.gif --HDP Don

Posted by: nprev Jul 18 2007, 02:19 AM

QUOTE (dburt @ Jul 17 2007, 07:07 PM) *
- we never claimed that the Meridiani spherules were "melt droplets or tektites" - they appear to be impact accretionary lapilli of unusual composition.

--HDP Don


Apologies, HDP Burt...missed that point in the argument, and I can only concur with that statement.

Your hailstone "eureka" does bring up an interesting aspect of this debate, though. Has anyone seen any evidence for accretion by whatever means in blueberries? Hailstones show layers, but the blueberries that Oppy has bisected within a matrix look pretty uniform. Of course, this may just reflect the behavior of the RAT (plus the fact that we can't blow off the residual dust), but this may also indicate that any accretional layering is very fine in scale--if it's there at all. Finer layers imply more gradual, perhaps even cyclical. formation processes.

Posted by: dburt Jul 18 2007, 02:22 AM

QUOTE (Shaka @ Jul 16 2007, 11:42 PM) *
Really, Don, that is the bottom line for me. Ever since Eagle crater I've been looking at this 'rock', and I just cannot believe that it is the result of the incomprehensible violence of impacts.
I stand in awe of impacts.
Where is that violence in the Meridiani evaporites? Where is the chaos? Where is the crushed matter?
You ask what at Meridiani cannot be explained by impact surge. I say "its totality".
Cheers,
Shaka

Shaka - There are no Meridiani evaporites. There never were, except perhaps in press releases. Each of the first 3 landers (Viking 1 and 2, Pathfinder) detected about 10% sulfates in soil. Duricrust (a moisture-related process resulting from capillarity) was suggested. Oppy detected about 30% sulfates as an improbable mix of highly soluble and nearly insoluble salts (almost no chlorides, which might indicate a true evaporite). To account for this improbable mix the MER team had to back off their initial playa/sabkha claims and hypothesize a totally invisible playa whose wind erosion led to these mixed salts (despite the fact that all terrestrial analogs consist purely of the insoluble salt, gypsum).

I agree with you that impacts are awesome. I don't think that you or most other people here are considering what happens if you impact soft sand, probably with interstitial ice, rather than flinty bedrock. In his 2003 Mars book William K. Hartmann predicted that most energy would be absorbed, and that the only result would be "a kablooey of dust and steam" or what we are calling an impact surge deposit. If you don't think it's "violent" to deposit perhaps several meters of sediment in a few minutes, perhaps you need to expand your definition. Shoot bullets into a sandbank and see what happens. Distant impacts into bedrock are permitted too, of course.

--HDP Don

Posted by: dburt Jul 18 2007, 02:27 AM

QUOTE (nprev @ Jul 17 2007, 07:19 PM) *
Has anyone seen any evidence for accretion by whatever means in blueberries?

The ones that have been RATed show no layering, but some of the broken ones do (including at least one imaged in the past few weeks). Our 2005 Nature paper illustrates a broken berry with layering. Of course, layering could be present in either concretions or accretionary lapilli, so we have to look to other indicators for a diagnosis.

--HDP Don

Posted by: dburt Jul 18 2007, 02:32 AM

QUOTE (CosmicRocker @ Jul 16 2007, 10:33 PM) *
It seems that Fe diffusion below a slowly changing water table matches the data as well as other models.

No it doesn't, because then the berries, rather than being randomly distributed in the rock, should be concentrated just below the alleged water table (as they are in the Navajo and Page Sandstones - the putative analogs for Meridiani sedimentology). Diffusion through a stagnant, pore-fluid brine is extremely slow.

--HDP Don

Posted by: nprev Jul 18 2007, 02:35 AM

QUOTE (dburt @ Jul 17 2007, 07:27 PM) *
The ones that have been RATed show no layering, but some of the broken ones do (including at least one imaged in the past few weeks). Our 2005 Nature paper illustrates a broken berry with layering. Of course, layering could be present in either concretions or accretionary lapilli, so we have to look to other indicators for a diagnosis.

--HDP Don


Don, do you have a link to that image, please? Very interested...

Posted by: dburt Jul 18 2007, 02:45 AM

QUOTE (ngunn @ Jul 17 2007, 03:10 AM) *
Thanks again for your reply. I do appreciate that nobody has explanations yet for all the details, but whereas the 'official' model has billions of years to work its tricks your scenario has to do it in, say, half an hour. I think that makes having a convincing model for the choreography vital to the credibility of the case you're making. At the moment you leave a lot of important parameters in soft focus, so it's not surprising that some people express a 'vague sense of unease' in response.

For a while I thought the nickel clue might be a piece of hard evidence one way or another, but I'm beginning to doubt that now. I did read what you said about it in your paper, but it doesn't seem like very strong evidence there. Likewise the rebuttal by Squyers et al., saying that the nickel isn't enriched enough for the iron to be meteoritic simply begs the question of what mix of meteorite and target rock would have gone to form the spherules - another enormous free parameter in your scenario. Yes I was hoping others would chime in but perhaps nobody sees much mileage in it.

ngunn - The "official" model doesn't have billions of years to work its magic - they have to do it while that part of Mars was somehow warm and wet long after all available other evidence indicates that the rest of Mars was cold and dry. Also, you can have as many impact surges as you want, spread out over as may billions of years as you want, so long as Meridiani was the target. Victoria itself probably generated a surge, which Oppy rolled right over without noticing anything amiss (I hope to address this in more detail in a future post).

If you understand, through the medium of the putative brine, likely Ni2+ partioning between good-fit Mg-phases and the misfit Fe3+ phase (hematite), the Ni argument is quite straightforward - there simply shouldn't be any in aqueously-crystallized hematite. You have to know something about about crystal chemistry and partition coefficients though.

--HDP Don

Posted by: dburt Jul 18 2007, 03:03 AM

QUOTE (helvick @ Jul 17 2007, 07:52 AM) *
That wasn't my intention (Honest!), I think that the hailstone-style formation model in an impact surge column\collapse seems like the easiest way to get the physical attributes the way they are. I'm just trying to see if the numbers that I'm able to hack together make it seem more or less likely. I haven't figured out which way it's leaning yet myself but I've got to admit I'd like to see it be possible - hematite hail has a nice ring to it.

Helvick - Thanks for the clarification. Keep in mind that the impact makes its own atmosphere - it vaporizes everything, even silicate rocks (briefly). Most of the turbulent cloud from which we hypothesize that the blue-gray hematite might have crystallized and been accreted would then have consisted of steam, presumably derived from vaporization of near-surface ice or very deep brine (plus minor contributions from hydrated and hydrous minerals). So the terminal velocity through the much thinner Martian atmosphere would be largely irrelevant. The turbulent could would contain lots of suspended solids too, contributing to its ability to support spherules. We're not particularly happy with that "hematite hailstones" model either (post-depositional oxidation and/or leaching of some other type of accretionary lapilli would be easier conceptually), but it's the only way we can think of to explain the blue-gray color of the spherules (something the concretion model absolutely fails to do - and even forgets to mention).

--HDP Don

Posted by: dburt Jul 18 2007, 03:18 AM

QUOTE (Aussie @ Jul 17 2007, 04:01 PM) *
Dburt
If I understand correctly you are proposing that that the spherules are hematite microkrystites that condensed out of the impact plume and then distributed through an extremely thick surge deposit rather than as a boundary layer. This stretches my imagination to a degree and there does not seem to be any evidence of tektites coincident with the microkrystites, or any evidence of splash forms or other melt products. The apparent thickness of the spherule rich layer does not fit a single impact layer scenario and the fact that the hematite rich area of Mars is limited to Meridiani indicates that hematite microkrystites are not a feature of impacts on Mars, or indeed to the best of my knowledge do they have a hematite analogue in Earth impact surge deposits. Or am I missing something?

Aussie - A warm welcome to a new face with new questions. As stated in previous posts, once you've made the high-temperature hematite spherules somewhere in Meridiani, by whatever mechanism, and deposited them however and wherever you like, you can depend on as many later impact episodes as you like to distribute them uniformly, spread out over as long a period of time as you like. Look at all the berries distributed by the Victoria impact. How many tectites or microkrystites do you see related to the Victoria impact, although I have heard no one suggest it was other than an impact (and you only see the heavily wind-eroded impact breccia exposed right at the edge of the crater)? As we have hypothesized from the beginning, clearly there was something unusual about Meridiani to initially form the hematitic spherules (in this we fully agree with the MER team) - we just don't know what. Was it the nature of the impactor (possibly a relatively rare metallic meteorite), the nature of the target (possibly containing a large Fe,Ni sulfide deposit, as proposed for Mars by Roger Burns), the size of the impactor (implying scaling up of small impact-related spherules that would normally be lost amongst the sand grains) or something else? We don't claim to know.

--HDP Don

Posted by: dburt Jul 18 2007, 04:22 AM

Well, time to quit again, and here are a couple more photos (now that I've laboriously taught myself how to embed them). These were taken on 3 Jan 2006 in the volcanic explosion surge deposits at Coronado Mesa, about an hour's drive out of Phoenix (part of the Superstition Mts. caldera complex). Knauth used ones like them to illustrate his LPSC talk that March - these were taken by me on the same occasion. The first shows a large cross-bed similar in scale (about a 3 m cliff) to that in Burns Cliff, with flat beds on top. Lots of violence (listening Shaka), but no paleo water table. The composition is pure rhyolite (silicic igneous rock) - you'd have been shredded and roasted in seconds.



The second shows polygonal shrinkage cracks in the surface of a lower-down surge bed - very similar to those so common in Meridiani (and very common in other surge beds). NOT mud cracks, not even close. Pocket knife gives scale.



Enjoy. No dust storm yet tonight.

--HDP Don

Posted by: ngunn Jul 18 2007, 01:15 PM

QUOTE (helvick @ Jul 17 2007, 03:52 PM) *
hematite hail has a nice ring to it.


You didn't tell me you had a tin roof. biggrin.gif

QUOTE (dburt @ Jul 18 2007, 04:03 AM) *
Keep in mind that the impact makes its own atmosphere


Yes, I am not forgetting this. For very large impacts the pre-existing martian atmosphere would probably have played only a minor role in shaping events. It is at this end of the scale, it seems to me, that you have most chance of producing relatively large haematite hailstones.

My reasons for reposting the link to that hydrology paper were twofold. First, because it seemed relevant to Nprev's geology question. I fully agree that it offers an explanation for the 'wet Meridiani' interpretation rather than for the observations directly. That leads me to the other reason - it is an example of a 'choreography' paper. It sets out a plausible cause, a plausible sequence of events and a plausible timeframe for that version of events. The equivalent for the surge hypothesis would surely have to involve a quantitative dynamic model of the impact and its aftermath.

I am proposing this as a way forward, not as an obstacle. In your position I would seek to proceed as follows:

1/ Take this question and separate it entirely from the Meridiani debate:- "Can a large meteorite impact with a rocky planet result in the production of abundant 5mm haematite accretion lapilli, and if so under what range of initial parameters?"

2/ Find an independent team of dynamic modellers willing to take it on, preferably people with no stake in the Meridiani question.

The outcome would be valuable whatever it was. If for example the answer was "Yes, but you need a planet with an atmosphere as dense as that of Venus and containing free oxygen" that wouldn't help you at Meridiani but it would be an interesting result in its own right and could be chalked up as a significant gain for the impact surge idea. Running a model would also firm up everybody's notions on what to expect in a Martian surge deposit and so help with recognising them in future. The excercise would also be sure to raise the profile of the whole subject of impact surges and maybe attract youngsters to the field.

Posted by: MarsIsImportant Jul 18 2007, 01:33 PM

Dr. Burt,

That crossbedding on that cliff you showed us has clear signs of high speed winds. No such signs are indicated within Burn's Cliff on Mars. You might suggest St. Mary's cliff; but, that face has fallen apart. Until we get a much closer look, any such evidence is easily disputed.

An impactor on Mars as big as the one you suggest would create high speed winds--like you said, it would create its own atmosphere. Such a large event should reveal itself fairly easily through topographic evidence. Where is the topographic evidence?

If your model is anywhere near the truth, then Meridiani should not be so unique.

Posted by: don Jul 18 2007, 01:44 PM

HDP don - Nice pictures, but more of terrestrial volcanic deposits (where are the impact deposits)? And you say my comments are biased with terrestrial blinders. wink.gif I don’t think anyone doubts that high angle cross bedding occurs in surge deposits associated with nuclear bomb or rhyolitic volcanic explosions (btw, wrong composition for meridiani). The cross beds in your photo appear poorly sorted and pyroclastic debris is quite evident along flow surfaces (at least with the resolution of my computer screen). Yep, that’s a miocene volcanic surge. Unless I missed something, we don’t see that at meridiani. Other then a cross bed, where is the connection?

I think Grotzinger (2005) calls the polygonal features “recent” dessiciation or dehydration features not contemporaneous with deposition. I tend to think the cracks you show are contemporaneous with deposition.

other don

Posted by: dburt Jul 18 2007, 10:21 PM

QUOTE (don @ Jul 18 2007, 06:44 AM) *
HDP don - Nice pictures, but more of terrestrial volcanic deposits (where are the impact deposits)? And you say my comments are biased with terrestrial blinders. wink.gif I don’t think anyone doubts that high angle cross bedding occurs in surge deposits associated with nuclear bomb or rhyolitic volcanic explosions (btw, wrong composition for meridiani). The cross beds in your photo appear poorly sorted and pyroclastic debris is quite evident along flow surfaces (at least with the resolution of my computer screen). Yep, that’s a miocene volcanic surge. Unless I missed something, we don’t see that at meridiani. Other then a cross bed, where is the connection?

I think Grotzinger (2005) calls the polygonal features “recent” dessiciation or dehydration features not contemporaneous with deposition. I tend to think the cracks you show are contemporaneous with deposition.

Other Don - Did I ever claim that those weren't volcanic deposits? See my post #278 for a statement on where the terrestrial impact deposits went, and earlier posts for why we have to use volcanic deposits as analogs. And how is the exact rock composition relevant to the internal morphology and structure of a violent explosion deposit? For the coarser pyroclastic debris in the photo, substitute "surge-transported blueberries" if it makes you feel better about what the photo is telling us.

The connection with Burns Cliff is that a purely impact or other surge process can produce a large eolian-appearing cross-bed cut off on the top by flat beds, such as we see exposed on Burns Cliff, without requiring an old water table (a.k.a. "Stokes surface" or "supersurface") for which there is absolutely no other evidence. I repeat, no evidence whatsoever (no shales, no mud cracks, no berry concentrations, no salt concentrations, nothing). Also, the Burns Cliff exposure has an unexplained and unaddressed channel-like gouge taken out of the left side of it, which is perfectly well explained by the surge hypothesis (as a vortex, such as those discussed by Sue Kieffer and several others for surge deposits) but is highly unlikely in a water-table controlled planar "supersurface". Grotzinger et al. (2005, EPSL, p. 48, Fig. 6a) refer to this channel in a figure caption as "scour and infill" as though that were perfectly explainable and expectable in terms of wind erosion and and an erosion-controlling water table. I'll give you a hint - it's not - not at all. Can you explain that scour in terms of their model? They appear to have hypothesized a "supersurface" ("Wellington contact") of regional extent on the basis of a single large cross-bed with a large channel-like scour taken out of the top of it - which scour, on the face of it, makes their hypothesis untenable. Do you disagree? If so, why?

If HDP Grotzinger inferred that the shrinkage cracks at Meridiani were recent and you inferred that those at Coronado Mesa were not, how is this relevant to their external morphology, which is the data? One of the biggest mistakes you can make in science, as I have emphasized repeatedly in this thread, and probably the biggest barrier to new discovery, is to confuse the actual data (observations) with what someone or other has inferred from that that data. Learn to make your own inferences if you want to make discoveries. The true beauty of the way the MER missions have been run (and I cannot praise NASA, Steve Squyres, Jim Bell, and the rest of the MER team enough for this) is that now we can all do that with photos and other data on the web.

BTW, I'm about to add a postscript to my post #278 on why terrestrial (and lunar) impact craters are probably a poor guide to Mars impact craters - so refer back to that if you're curious. In my initial reply last night I completely forgot to mention the unique subsurface cryosphere of Mars and the abundance of easily-scoured sand and dust on the surface.

I enjoy learning from you.

--HDP Don

Posted by: dburt Jul 19 2007, 12:25 AM

QUOTE (nprev @ Jul 17 2007, 07:35 PM) *
Don, do you have a link to that image, please? Very interested...

nprev - Here's the image my always rose-colored memory recalled seeing recently:
http://qt.exploratorium.edu/mars/opportunity/micro_imager/2007-06-29/1M236138185EFF85R9P2956M2M1.JPG

However, on looking at the bottom center berry again, it's certainly not very convincing (the apparent darker zone is off center, and doesn't carry across the edge, plus a similar discoloration is seen on other, unbroken berries, presumably owing to their having been pressed or scraped). MI images of some of the broken ones from earlier in the mission are far more convincing in terms of zoning (including the photos reproduced in our 2005 Nature paper - Fig. 5d from sol 28 and Fig. 5e from sol 142). In any case, as mentioned in my original post, zoning is not diagnostic of either accretionary lapilli or concretions - they both can display it.

Too bad Oppy's MI has not been able to "stop and smell the spherules" more as it has circumnavigated Victoria Crater. We might have learned something about their response to impacts. At first glance, they certainly look no different for having been shocked by impact and excavated from the crater. As mentioned in previous posts, this presumably reflects the friability (poor cementation) of the Meridiani rocks. The Victoria cratering event probably was somewhat analogous, at a far larger scale, to shooting a bullet into a pile of sand. That is, most of the energy was absorbed by internal heat and vapor generation rather than being transmitted as shock waves - very unlike impacts into hard, solid bedrock.

--HDP Don

Posted by: dburt Jul 19 2007, 02:15 AM

QUOTE (ngunn @ Jul 18 2007, 06:15 AM) *
....
My reasons for reposting the link to that hydrology paper were twofold. First, because it seemed relevant to Nprev's geology question. I fully agree that it offers an explanation for the 'wet Meridiani' interpretation rather than for the observations directly. That leads me to the other reason - it is an example of a 'choreography' paper. It sets out a plausible cause, a plausible sequence of events and a plausible timeframe for that version of events. The equivalent for the surge hypothesis would surely have to involve a quantitative dynamic model of the impact and its aftermath.
....
1/ Take this question and separate it entirely from the Meridiani debate:- "Can a large meteorite impact with a rocky planet result in the production of abundant 5mm haematite accretion lapilli, and if so under what range of initial parameters?"

2/ Find an independent team of dynamic modellers willing to take it on, preferably people with no stake in the Meridiani question.
...

ngunn - Thanks for your reply. I regard that hydrology hypothesis as merely an extension of the original hypothesis (artesian spring = desert oasis). Without the original hypothesis, it has no reason to exist, and there is no independent evidence in favor of it. If you're sufficiently clever, and the authors certainly are, you can model practically anything plausibly if someone else has specified the desired result in advance. A recent summary of that hydrology hypothesis is provided in this abstract from last week's Mars meeting:
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3173.pdf

Note that on the third page, the abstract recognizes that permanent high groundwater acidity is highly implausible (something the original MER team hypothesis failed to recognize), then accounts for temporary high groundwater acidity at Meridiani by misquoting MIT's late Roger Burns (who as a brilliant geochemist never proposed what they claim he did). The authors state: "Following the model of Burns [16-17], the mildly oxidizing fluids would have reacted with pyrrhotite in the basaltic aquifers, producing substantial acidity and liberating dissolved ferrous sulfate." This way of producing the putative acid groundwaters at Meridiani sounds plausible only if you know nothing about the relation of the water table to sulfide oxidation in mineral deposits. The reasons it sounds highly implausible to me are 1) after travelling underground through hundreds of km of finely divided, FeO-rich basalt, the groundwaters would be highly reducing, not oxidizing, and 2) sulfide oxidation in mineral deposits can only happen ABOVE the water table, in the so-called zone of aeration (a.k.a. vadose zone). In fact, new sulfides are deposited just below the water table (so-called supergene enrichment, which typically produces the highest grade ores). Roger Burns knew all this and his gossan model for Mars therefore depended on sulfides being oxidized only ABOVE the water table.

Inasmuch as the MER team hypothesis has a rising water table being continuously at or above the ground surface, subsurface sulfide oxidation to produce the alleged groundwater acidity seems impossible on the face of it. An obvious internal contradiction. (Our impact model proposed post-depositional jarosite formation via Burns-style oxidation of finely divided sulfides above the water table, although it does not depend on it - jarosite could alternatively be formed by reaction with acid vapors in the steamy surge cloud.) The bottom line to me (temporarily wearing my geochemist hat) is that the second hypothesis seems no more plausible than the one on which it depends, and likewise contains several internal contradictions, from a geochemical if not hydrological perspective.

Regarding your numbered suggestions, we regard the answer to the first question as "yes" solely because we can see no other even mildly plausible way of making the hematitic spherules and accounting for all of their properties. If you can suggest a better way, you can be first author of the resulting paper (and can then have the huge warm, wet Mars crowd abuse you instead of me smile.gif ). Our current starting parameters are only 1) that Mars seems to be an exceptionally Fe-rich planet (its basalts, sampled and driven into space by impacts and then landed on Earth, are 2X to 3X as Fe-rich as terrestrial basalts), 2) that it seems to be an exceptionally salty planet, possibly owing to global loss and/or freezing of its originally huge hydrosphere (salty oceans) and 3) salty, steamy vapors produce blue-gray hematite flakes as a very common insoluble mineral in terrestrial fumaroles, even in extremely Fe-poor volcanic systems. Steamy salty surge clouds on Mars should be analogous, and should produce blue-gray hematite too.

We regard the second goal as highly laudable, but currently unattainable. Any dynamic modellers interested in Mars currently "have a stake in" Meridiani, one way or another.

Thanks for your comments and recommendations.

--HDP Don

Posted by: dburt Jul 19 2007, 03:54 AM

Well, that seems to about cover Mars impacts for tonight. Attached find a couple of photos of fumarolic blue-gray (specular) hematite flakes that I took several years ago for a different purpose (no scale available, but the field of view is about 1 cm). The locality, studied in 1983, is Tepetates, San Luis Potosi, Mexico, an extremely Fe-poor volcanic system (a group of large rhyolite domes), yet hematite flakes like these are still very common in the fumarolic deposits. The larger pinkish crystals that the blue-gray hematite flakes are growing on is the fluorosilicate topaz and it's presence indicates that the steamy, salty, acidic fumarolic vapors were rich in fluorine as well as chlorine and iron.





These photos possibly demonstrate that a giant steamy, salty impact system on iron-rich Mars might well have precipitated many trillions of nano-scale hematite flakes in a turbulent, condensing, dark vaporous cloud, that these in turn could have accreted into billions of tiny hematitic spherules that eventually ended up in the rocks and on the surface at Meridiani. Sure sounds like Burt's Believe It or Not, doesn't it? biggrin.gif Oh well, if you can come up with a better explanation for those blue-gray spherules, my hat's sure off to you (concretions just won't cut it, I'm afraid, for all the reasons I've already enumerated at length).

--HDP Don

Posted by: ngunn Jul 19 2007, 09:08 AM

I'll be here less often for a bit - it's time to appreciate landscapes closer to home. Thanks to all, most recently to dburt for that long patient nickel explanation. (Yes I do understand it a bit better now but not really well enough to comment.)

I hope you find an objective, hard-science quantitative test of your ideas somewhere, even if it's not the one I suggested. I think that's what it would take to make people less dismissive. Purely descriptive arguments (however good) just won't do the trick, I fear, once positions are this polarised.

Of course there's always the possibility that the other party will construct a numerical model to try to prove the hailstones are impossible - and end up knee-deep in virtual hailstones!

Posted by: nprev Jul 19 2007, 09:12 AM

Thanks for the link, esteemed HDP! smile.gif

Gotta say, though, I really don't see any concentric features on them berries. What does strike me is that many of the 'early' berries back near Eagle that were embedded in matrix or exhumed via wheel trenching had odd, bumpy surfaces, seams, etc. while this particular set (in fact, the majority of those examined at other locales) seem much more homogeneous in terms of surface texture.

I suppose that weathering of exposed berries is the most likely explanation, but the dichotomy is a bit puzzling and perhaps perceptually misleading. The smooth ones do look a lot like condensates that would be congruent with your general hypothesis within your scenario(s), but what of the bumpy berries? Fine features like that would not be expected (in my opinion, at least) to occur on rapidly forming gaseous or liquid condensates due to the flow and consequent erosive action of the surrounding medium.

Okay, here's my alternative hypothesis for berry formation: [EDIT: several hours pass as I stare at my screen...] Okay. There are two types of blueberries. Type I berries are hematite concretions with distinctive, odd surface textures formed by repeated H2O saturation as evidenced by the extensive sedimentary deposits in Meridiani. Type II berries are artifacts of many, many meteoritic impacts in the region during wet periods characterized by smooth surfaces due to their relatively rapid formation and cooling. Both types are chemically similar due to the fact that they both precipitated out of the same matrix and very similar aqueous solutions; the significant variable that produces morphological differences is duration of favorable conditions for formation.

Send me my Nobel Prize or a dunce cap now, whichever is most appropriate... tongue.gif Also, just for fun, here's a http://photojournal.jpl.nasa.gov/jpeg/PIA06166.jpg of the biggest Type I berry-analog in the whole Solar System...

Posted by: Bill Harris Jul 19 2007, 01:20 PM

QUOTE
...many trillions of nano-scale hematite flakes in a turbulent, condensing, dark vaporous cloud, that these in turn could have accreted into billions of tiny hematitic spherules...


About as likely as frogs spontaneously generating from mud. wink.gif Interesting belief, but where is your proof?

From the many MOC and MRO images taken of the Meridiani Plains where is the indication of the brine splat/base surge?

--Bill

Posted by: Aussie Jul 19 2007, 02:06 PM

Dburt,
You make the case that Mars basalt is Fe rich, the planet is exceptionally salty and salty, steamy vapours produce blue-grey hematite flakes as a very common insoluble mineral in terrestrial fumaroles. So when an impact occurs steamy salty surge clouds on Mars should be analogous, and should produce blue-grey hematite nano-scale hematite flakes that would condense and accrete into the spherules. But this scenario requires almost instantaneous oxidisation of the basalt Fe content. Michelle Minitti et al found that it took 3 days at 700 C to oxidise a 0.1 to 0.6 um hematite coating on a mars meteor composition in a CO2 environment. http://minitti.asu.edu/publications/abstracts/hem_ab.pdf
I appreciate that you have argued that the surge cloud will create its own atmosphere, and vapourisation as well as melt is involved, but I still have reservations over the speed at which this process must occur. I find the scenario hard to accept in the absence of any rigorous modelling or terrestrial analogue, and in the light of Minitti’s results. Not impossible, but the sequence of events necessary to form hematite spherules seems far more complex and problematic than the formation of terrestrial impact microkristites.

Also, if this combination of impact energy and martian basalt can produce the spherules, why has this process not occurred in a number of impacts rather than being isolated to a few comparatively small regions? And the regions where grey hematite has been identified (Aram Chaos, and Ophir and Candor Chasma in Valles Marineris ) all have indicators for aqueous activity in the distant past. This seems to point to an aqueous rather than impact cause.

I understand that Geothite can transition to hematite in temperatures as low as 70 C in saturated water vapour given that in an aqueous system, crystal growth effects lower the transition temperature from that required in the dry state. (Catling and Moore Icarus 165 (2003) 277–300). So there is potential that low levels of hydrothermal energy could have created the appropriate conditions for hematite conversion from a goethite spherule precursor in Mars’ early life. A scenario possibly as tenable as impact accretion.

Posted by: centsworth_II Jul 19 2007, 03:02 PM

QUOTE (Aussie @ Jul 19 2007, 10:06 AM) *
Also, if this combination of impact energy and martian basalt can produce the spherules, why has this process
not occurred in a number of impacts rather than being isolated to a few comparatively small regions?

In connection with this question, my impression is that the hematite signature of the Meridiani region forms a confined shape with a fairly defined edge. I would expect that if the hematite was formed by large impacts that it's signature would be more widespread, with less shape and definition. Each large, hematite producing impact would shoot a surge out radially. In my mind, I have to imagine the hematite from a series of impacts being shot toward what would become the Meridiani region and not shot outward in other directions. From space, it looks like the hematite of Meridiani collected there rather than shot there by impact. Why was hematite not shot in directions away from Meridiani as well?

Posted by: ElkGroveDan Jul 19 2007, 09:50 PM

QUOTE (centsworth_II @ Jul 19 2007, 07:02 AM) *
Why was hematite not shot in directions away from Meridiani as well?

Great question. And I bet Don has an answer.

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