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/200512/200..._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.p...surge&st=30

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

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! )

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

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

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?) 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

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 )

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

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.

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... )


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.


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

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.

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

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!)

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)"... ...please don't worry about that, we love it!

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?
Click to view attachment
(Source image)

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.

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... )

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...

-the other Doug

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.

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.

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

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

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

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.

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.

--Don

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.

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?

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

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.

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

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?

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.

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.

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).

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

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

Superb question! Really sets me off (the flattery doesn't hurt either ). 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...).

...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.

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

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

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.

You are wrong.

--Bill

And besides the large amounts of liquid water involved in the original
formation of the salts, right?

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.

--Don

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

--Don

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?

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.

--Don

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

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

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

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) . 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 ).

--Don