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.

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.

--HDP Don

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

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.

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

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.

Sorry to rant - you seem adept at pushing my buttons. And keep chipping away - I'm truly grateful for your efforts.

HDP Don

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.
That would be fun, and maybe more fun if we could see which way we each voted.

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. 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

...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?

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. 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. Or would you prefer a classroom demonstration? )

--HDP Don

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

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:



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.

...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



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.

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.

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.

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.

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.

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.



Meteor impact...sounds like parts of Dr. Burt's model. They already considered it from the beginning.

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.


But did they think of base surge from the beginning?

Glotch et al 2006 "Fresnel modeling of hematite crystal surfaces and application to martian hematite spherules"

Burt:


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.pdf that 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>

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.

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.

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.

--HDP Don

Geothite with hematite...it looks fairly Martian to me.

http://ocw.mit.edu/ans7870/12/12.108/f04/i...b1/lab1-16.html

...very much like Meridiani, at least in a general sense.

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.

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.

--HDP Don

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

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. Thanks again.

--HDP Don

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? ).

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

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.

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

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.

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. Just park at the MacDonald's in Page, Arizona and start hiking north along the Rim Trail...

--HDP Don

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. 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

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: Squyres et. al. (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:
Knauth-Burt-Wohletz.

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...). 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

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?

Did I miss any?

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

hendric - Thanks for your original thoughts. If none of them strike you as special pleading, perhaps you are a true believer. 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...

--HDP Don

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?

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.

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 - 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.

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.

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/10.10...110703321632408

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.

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.

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

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

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.

...Solution to many observational problems--HiRISE. Also, Triangulation is fairly easy.

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.