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Welcome Professor "brine splat" Burt, "a chance to ask questions... or raise objections"
centsworth_II
post Jun 15 2007, 08:37 PM
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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/200512/200..._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
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dburt
post Jun 16 2007, 02:11 AM
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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
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nprev
post Jun 16 2007, 06:51 AM
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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 )


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centsworth_II
post Jun 16 2007, 03:08 PM
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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]
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Bill Harris
post Jun 16 2007, 05:58 PM
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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


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dburt
post Jun 17 2007, 08:12 AM
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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
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djellison
post Jun 17 2007, 08:45 AM
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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 )
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Bill Harris
post Jun 17 2007, 11:25 AM
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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


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nprev
post Jun 17 2007, 01:49 PM
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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.


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dvandorn
post Jun 17 2007, 03:28 PM
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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


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centsworth_II
post Jun 17 2007, 05:31 PM
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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.
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dburt
post Jun 18 2007, 12:00 PM
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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
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centsworth_II
post Jun 18 2007, 02:54 PM
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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!)
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nprev
post Jun 18 2007, 04:29 PM
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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!


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centsworth_II
post Jun 18 2007, 04:47 PM
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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?
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