[X] My Assistant

[dburt]

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

[dburt]

Let me quote directly from the Glotch paper itself:
I stated myself that it was only one piece of evidence. This was a laboratory experiment and just one comparison study. It is convincing but not absolute.

....more posts to follow soon.

MarsIsImportant - What you quote is not any type of evidence but an inappropriate conclusion. You need to learn to recognize the important difference between data and interpretations of that data. It was a probably meaningless laboratory experiment which I have no intention of repeating. Feel free to do so yourself, however - reproducibility of results is the essence of science.

--HDP Don

[dburt]

A quickie - Why only haematite? Where are all the 'hailstones' made from the many other materials that presumably condense out of an impact surge in similar fashion? Oh . . I know - leached away by groundwaters.

ngunn - Thanks for the specific question, although it has already been answered here. As an impact surge cloud travels outwards and turbulently mixes with the atmosphere, the vapors in it expand, cool, and condense. As with evaporation in a lake predictably crystallizing a series of salts according to increasing solubility (in the case of sulfates, least soluble gypsum first, and most soluble Mg-sulfate last), so also various things will condense sequentially out of a cloud according to their volatility and the gradual chemical changes occurring. It is entirely reasonable to expect one phase to form at one time and place, and others at other times and places (as in an evaporating lake). If any of the phases formed were highly insoluble, such has hematite, their form would persist unaltered, whereas more soluble condensates, such as salts, would recrystallize after deposition. No groundwaters needed - only a salty, steamy, condensing cloud.

That was pretty good question. Thanks again.

--HDP Don

[dburt]

I am far from being a geology expert, but I am a chemist.

I don't understand why the argument is one...or the other. I haven't seen any reason why both mechanisms could be operant at different times, and/or why one excludes the other. It does seem to me that "surges" can and do account for some observations, in addition to the MER team hypothesis.

Silyene - Indeed, many geological arguments work out that way - both partly right, at least some of the time. In the present case, IMHO, impact surge accounts for everything the rovers have yet found in fine-grained bedrock, so there is no need to invoke any of the complex series of Earth-like events proposed by the MER team. Future observations, such as the finding of lake beds, might change that conclusion. We're not holding our breath in the meantime.

We agree with them that the dissolved salts originally formed in liquid water, via neutralization of acids by bases. No one has ever suggested any other geologically reasonable way to make dissolved salts in large abundance. We also agree (although my co-authors and I brought the problem up first) that the improbable mixture of soluble and insoluble salts cannot be a primary evaporite - some sort of transportation and mixing event must have taken place (impact by us, wind off a vanished playa by them). We finally agree with them that water was essential to form and cement the rock, only we think that the water was condensing steam, and they make it a series of at least 4 different groundwater brines doing various improbable things below and above the surface and leaving no unambiguous trace of their passage. (Can you tell I'm a bit biased? ).

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

[ngunn]

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.

[dburt]

...to respond to post #210
Not all of the lapilli would be expected to completely solidify before hitting the ground. So we should also expect some evidence of deformity of some spherules that is indicative of impact. I know of no examples. I will be on the look out for them.

MarsIsImportant - You are confusing your expectations for Mars (or nature in general) with the way it actually behaves. Impact spherules do not impact the ground like hailstones falling through air - this has been covered in many previous posts. They are carried along with the flow and turbulently mixed with everything else. Accretionary lapilli in terestrial volcanic surge deposits never display the microcratering behavior you ascribe to them, despite Earth's more powerful gravity. Why expect that behavior on Mars, if it is never observed in terrestrial analogs? Do your homework please.

--HDP Don

[MarsIsImportant]

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.

[dburt]

And thank you too for the specific answers. So it's the cooler surface-plating process we're to consider. I'd like to know how long you think this takes - indeed how long you think these objects spend above ground between the impact and the deposition. There is presumably no convective cell structure analogous to what keeps terrestrial hailstones airborne in updraughts long enough to get quite large.

You didn't offer an opinion on what the Glotch work excludes and what it doesn't. Maybe someone else could help here.

On the 'why only haematite' question - I did read your earlier post about how the impact surge could sort materials. That's fine, except I wouldn't expect it to be 100 percent efficient. I am aware that Meridiani was selected because of the prior detection of haematite, so yes you could say 'that was where the haematite fell'. But then why would that mean that nothing else fell there in hailstone form? The haematite is the only such species to resist degradation over long periods? Are we talking about one event or many? Is there a signpost up at Meridiani saying 'Only drop haematite here?'. I think that's beginning to sound like special pleading.

At the very least you have been most unfortunate. The only mineral to provide surviving hailstones also happens to be one which habitually forms spherules in another way!

Ngunn - My compliments. It is thanks largely to you that this discussion has "grown up" for the moment. In a previous post I hypothesized that minutes to hours might be needed to form the spherules, and that the convective structure might well be the mushroom-type cloud found above large volcanic and nuclear explosions (analogous to a thunderhead forming hailstones by condensation in air). What volcanologists call "column collapse" (or "downburst" in a thunderstorm - forming radial outflowing desert dust storms in Phoenix) seems probable in the low density atmosphere of Mars - this would form a high velocity particulate surge cloud carrying the tiny spherules along with the radial flow.

I already did offer a perhaps too outspoken opinion on the Glotch work. It is irrelevant to the discussion. They constructed their own straw horse and shot some arrows into it. We were always standing elsewhere.

Why mainly hematite? Probably because it is the only (or the dominant) insoluble mineral that formed. Active fumaroles are famous for forming a huge variety of interesting crustiform salt-type minerals by condensation from steam. Once the fumarole has died, what typically survives are only the water-insoluble oxides like specular blue-gray hematite flakes, cubes of black bixbyite, or rounded masses of brown cassiterite - respectively oxides of Fe, Mn, and Sn. You may also get insoluble fumarolic sulfates like alunite (Al) or jarosite (Fe). For special, fluorine-rich magmas that I once spent several years investigating, you can also get insoluble fumarolic silicates like gem topaz and silica phases (and occasional red gem beryl). In the case of Mars impact surge clouds, in addition to salts and brines, you may well have condensed actual hailstones or snow at the far distant, colder end. Ice in small amounts would obviously not survive, especially in the company of salts. Former chloride salts or even ice may be responsible for the crystal-shaped cavities and general high porosity of the Meridiani beds.

As covered in earlier posts, strictly speaking, you only have to drop the hematite spherules in a single area or zone. If the high velocity and turbulent energy of the radially outflowing surge cloud does not distribute them across the whole of Meridiani Planum, later impacts will. Look at what Victoria Crater did to distribute spherules - as I'll probably discuss more fully in a different post. The reason hematite is so obvious at Meridiani probably has more to do with the wind stripping a large planar area uniformly, leaving a lag (we completely agree with the MER team on this) than it does to its original conditions of deposition. Hematite-rich spherules may well be common elsewhere on Mars, just not exposed or too small to form a lag (or perhaps not - no real basis for saying). No special pleading is needed, in any case.

I don't think we've been unfortunate. Oppy has managed to survive long enough to image millions of berries over a 10 km traverse, not just the ones seen initially in Eagle Crater. Statistics now rule them out as concretions, as covered in previous posts. Concretions are nodules, lumps, masses, and ledges formed in a rock by fluid mixing - there are no constraints whatever on their overall shape, maximum size, or degree of aggregation, but they are constrained to be restricted to zones where fluids have flowed and mixed. The observed size and shape properties alone rule the berries out as concretions (as do their elevated Ni content and blue-gray, blue-gray color, and their distribution pattern in the rock). Anyone who claims otherwise is not using his eyes or common sense, IMHO. Do the actual field work yourself on Earth if you disbelieve me - don't let Oppy do all the heavy lifting on Mars. Just park at the MacDonald's in Page, Arizona and start hiking north along the Rim Trail...

--HDP Don

[dburt]

Professor the evidence for groundwater at Meridiani is so overwhelming that I cannot believe you would say what you just did. Previously you admitted that there was groundwater evidence; now you are saying there is no positive evidence for it. You are simply leaving it as an open question; however, it is not. I thought the issue that your model contested was merely against playa lakes and the origin of these sediments. Without groundwater, even your model fails miserably.

I've come to the conclusion that doing research for you is a complete waist of my time. Here is an internet address where you can find all the evidence you need to change your mind about water's role at Meridiani.

http://marsrovers.jpl.nasa.gov/home/index.html

I suggest you look through all the raw images too. That way you don't have to read all of the so called errant interpretations. In those raw images you will find everything that you claim is not there. Good Luck.

MarsIsImportant - Umm. What did I just say? I have never denied abundant salty groundwater on Mars. In fact, between 2000 and 2003 I published several papers proposing concentrated subsurface brines when it was politically incorrect within NASA even to mention the b-word. Again, please do your homework. I am just saying that, IMHO, there is no direct physical or chemical evidence that salty acid groundwater ever rose stepwise as a series of different brines through the salty Meridiani cross-beds, flowed ankle- to waist-deep across the level surface making current ripples, and sank back into the subsurface, meanwhile growing uniformly tiny spherical concretions randomly in the rock. There is also, for the moment, no physical evidence of any vanished playa lake. If you dispute this interpretation, please specify what data you are citing, rather than merely citing other scientists' interpretations that may be opposed to mine. I'm already well aware that many scientists choose to disagree with me, for their own reasons.

If you have been "doing research for me" you have a rather strange way of showing it. Still, I am grateful for your thoughtful comments and for the chance they have given me to lecture you on the nature of science. Unfortunately, that's too much like what I get paid to do every day. 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

[tfisher]

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.

[dburt]

I'm a bit surprised at that 300-400C number - that doesn't seem like a particularly low temperature to me and I can't see how that ties up with the rest of the "concretions forming in a brine" hypothesis. Where exactly are we going to find a 300-400C brine?

Anyway my current question for HDP Burt is whether the additional detail in that referenced paper actually does prove that the hematite at meridiani is unlikely to have formed at the types of temperatures implied by impact surge hypothesis.

helvick - Sorry for the delay in getting to you. In the meantime, I believe I've already answered your question. Glotch dry roasting things to 700 C, or even 300 C, is probably irrelevant, inasmuch as salty steam condensation probably occurs at lower temperatures, and he didn't grow anything hydrothermally, as far as I can determine. I fully agree with you that 300-400 C is just a bit warm to be growing sedimentary concretions, even in Phoenix in the summer, let alone Mars in the subsurface (where temperatures are multi-year averages, winter and summer).

He wrote that 2004 JGR paper you cited (which he perhaps now regrets, as we all do former hypotheses) when Meridiani was hypothesized to be a large metamorphosed iron formation, heated to 300 C some time after sedimentary deposition, in order to account for the specular or high-temperature blue-gray nature of the hematite as determined from orbital spectroscopy (an earlier hypothesis had been a super-giant hot spring). Once the concretion hypothesis for the spherules was born shortly after Oppy landed, the high temperature nature of the blue-gray hematite in them was not mentioned again, as far as I am aware. (And I admit again that my co-authors and I had quite forgotten about it until my posting here started those creative juices flowing again...). 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

[hendric]

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?

[dburt]

I've been doing a little reading to try to catch up on this thread. (I'm not there yet; there really is a lot of content here!) Anyway, I just wanted to point out the MER team's response to the original "brine splat" paper. This brief article doesn't seem to be up anywhere google can find, other than google's own memory of it: [url=http://google.com/scholar?q=cache:www.astro.cornell.edu/~banfield/nature2.pdf+]Squyres
Knauth-Burt-Wohletz.

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

[dburt]

I might have missed too much of the discussion already, but here are some of my thoughts on the dead grandmothers:

1. Brines moving up and down/disappearing: The obliquity on Mars changes much more severely and quickly than on Earth, due to not having a large moon. When the climate gets cold enough, the water in Meridiani froze out, then migrated to the poles, drying out the beds. When the climate warms up again, the returning water doesn't necessarily have the same composition as pre-ice age.
2. Porosity of the rocks: The freezing at the end of each cycle drives the grains apart, preventing them from sealing shut.
3. Distribution of the spherules + lack of solid masses of spherules: How well do we understand concretion creation (say that ten times fast!)? Do they require a "seed" at the center? If so, the seeds could be relatively uncommon, transported to Meridiani by wind, mixed with the sand/dust of the layers. Their relatively low abundance would not allow for large masses of concretions. The Navajo sandstone has another thing going for it: life! They've found life deep underground; the distribution of concretions in the sandstone could be modified by life in the rock, or in the original sand. See <a href="http://geology.utah.gov/online/pdf/pi-77.pdf" target="_blank">http://geology.utah.gov/online/pdf/pi-77.pdf</a>
4. Not enough odd shapes (individual concretions): The shapes of the concretions are driven by the environment. I see no problem with more round concretions due to
   1. Lower gravity on Mars
   2. Lower depth of burial on Mars
   3. Porous rock
5. Specular hematite: Sorry, my grandmother passed away. Can I get a pass?

Did I miss any?

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

[ngunn]

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?