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The Great Meridiani Debate
abalone
post Dec 23 2005, 08:30 AM
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QUOTE (dvandorn @ Dec 22 2005, 11:58 PM)
I'm still in the early-water camp, because there are established and understandable mechanisms by which Mars' climate could have evolved from a higher-air-pressure, much wetter environment to its current low-pressure, bone-dry existence.  The "contrived" mechanisms that have been proposed to explain relatively small-scale fluvial-appearing features fail (for me) on a number of levels, including the fact that they don't account for how widespread the fluvial and other water-related features (such as the Meridiani sulfate-rich sedimentary deposits) actually are.

So, for me, "Blue Mars" works better than "White Mars."  But YMMV.

-the other Doug
*

I'm with you and hoping but are we letting our judgement be clouded by wishful thinking?

My recollection is that Gusev Crater was supposed to be one of these places "with widespread fluvial and other water-related features". So far only an ocean of basalt sponged over with a wet rag is all we have seen.

It is worth remembering that the early Mars "could have evolved from a higher-air-pressure, much wetter environment" but 4billion years ago the solar output may well have been 40% less than today and Mars may have in fact have been colder than today. Brief events of volcanically heated water before it all froze solid may be the best we get.
The global distribution of pyroxene and olivine is difficult to reconcile with a wet past
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nprev
post Dec 23 2005, 08:38 AM
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QUOTE (abalone @ Dec 23 2005, 01:30 AM)
My recollection is that Gusev Crater was supposed to be one of these places  "with widespread fluvial and other water-related features". It is worth remembering that the early Mars "could have evolved from a higher-air-pressure, much wetter environment" but 4billion years ago the solar output may well have been 40% less than today and mars may have in fact been colder than today.
*


On that note, let's not forget about the Tharsis uplift and the atmospheric effects of long-term episodic vulcanism. Periodic atmospheric pressure increases from heavy outgassing (the effluent presumably would also include water vapor) might have not only allowed liquid water to exist on the surface for prolonged periods, but also facilitated melting of permafrost and subsurface ice from greenhouse warming. After the volcanoes shut off for awhile, the atmosphere thins out again, the water freezes out, and another layer at Meridiani is formed...? huh.gif


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nprev
post Dec 23 2005, 08:53 AM
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A little more on the post-volcanic freeze-out scenario: After the atmospheric pressure falls down to near present levels, ice at equatorial locations sublimes into vapor during the summer and eventually ends up in the polar/subarctic regions. The cycle repeats and redistributes water globally when the volcanoes get froggy again.

The very thin layers observed in the Meridiani sediments might lend credence to this theory. The warm periods might not last very long at all, and in the meantime the dust keeps on a-blowin' (in fact, probably with considerably more vigor), and thus offer a counterbalance to the greenhouse effect by increasing the planet's albedo during global storms. Once the storms subside, things warm up again and the dust settles where it will. Meridiani would look like a giant mud pit during these periods as the dust gums up nascent puddles.


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Guest_paulanderson_*
post Dec 23 2005, 09:48 AM
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QUOTE (abalone @ Dec 23 2005, 12:30 AM)
My recollection is that Gusev Crater was supposed to be one of these places  "with widespread fluvial and other water-related features". So far only an ocean of basalt sponged over with a wet rag is all we have seen.

The global distribution of pyroxene and olivine is difficult to reconcile with a wet past
*

Well, Spirit has found evidence for water alteration, although not as "exciting" as Opportunity. But again, as noted previously, it has also found evidence for clay deposits on Husband Hill and traces of carbonates. There is also (again) the global distribution of clays, albeit isolated patches so far (although widespread), found by Mars Express.

I don't know how this reconciles with the olivine, but it can't be just ignored, either. The clays in particular, as currently understood, would have required less acidic and longer-lasting water to form (although still limited to very early in Mars' history apparently). This has also been mostly ignored in the flurry of news reports the last couple days re the new CU Meridiani "revelations" which started this thread...
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Burmese
post Dec 23 2005, 01:39 PM
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It must be a frustrating position to be in to produce new papers using the complete Mars data set as released by the MER team knowing the MER team has a great deal more recent data that only they have access to which might contradict the outsiders' papers.
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helvick
post Dec 23 2005, 02:06 PM
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QUOTE (Burmese @ Dec 23 2005, 02:39 PM)
It must be a frustrating position to be in to produce new papers using the complete Mars data set as released by the MER team knowing the MER team has a great deal more recent data that only they have access to which might contradict the outsiders' papers.
*

True - but the MER team does deserve to have the first crack at things and they have an obligation to make sure that the data is fully validated before opening it up for everyone. After all they are the ones who put the long term effort in to get the mission and its instruments up there in the first place.
And no-one forced the UC team to publish without the additional data - they could choose to wait to see if it would reinforce or contradict their paper but getting it out early might well be more important and that's not an uncommon dilemma even for the main scientific teams.
The bad reporting on this is a bit disappointing but overall it seems to be generating good healthy discussions on the science.
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tty
post Dec 23 2005, 05:43 PM
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QUOTE (abalone @ Dec 23 2005, 10:30 AM)
The global distribution of pyroxene and olivine is difficult to reconcile with a wet past
*


Imagine that all Earth's water froze out at the poles just 200 million years ago. Something like 75% of Earths surface would be covered by fresh, unaltered volcanics by now (=all ocean bottoms, Deccan, Ethiopia, Snake River/Columbia plateaus, Iceland, Ontong Java plateau, Kerguelen plateau, CAMP etc etc).
This despite the fact that most of the Earth's surface would have been covered by water, and all of it modified by water for the first 95% of its history.

If there was water on Mars only pre-3,5 bya I think the odd thing is that so many traces still remain.

tty
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Guest_paulanderson_*
post Dec 23 2005, 08:28 PM
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I received an interesting e-mail this morning from Tom McCollom at Colorado University, one of the authors of one of the new research papers in question. Quote:

"First, we considered in our our article all of the chemical compositional data that have been published to date. The chemical compositions on which the more recent interpretations mentioned by Steve Squyres are based have not been published, and the MER team refused us access to these data when we requested. However, based on what we have seen in recent publications and information presented at conferences, there is nothing in these new data that would be inconsistent with our volcanic scenario, contrary to the claims that Squyres has made in the mass media. We intend to demonstrate this as soon as the data are made available to the broader scientific community."

This will be a long debate...

More articles also:

ASU geologists suggest Mars feature linked to meteorites, not evaporated lakes
http://www.asu.edu/news/stories/200512/200..._meteorites.htm

Mars Not so Wet After All?
http://www.nature.com/news/2005/051219/full/051219-10.html

And a new phyllosilicates abstract:

Phyllosilicates on Mars and implications for early martian climate
http://www.nature.com/nature/journal/v438/...ature04274.html
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tty
post Dec 23 2005, 11:02 PM
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These ASU people are positively dotty:

QUOTE
Impact surges "present a simple alternative explanation involving deposition from a ground-hugging turbulent flow of rock fragments, salts, sulfides, brines and ice produced by a meteorite impact," the three state in their article "Impact Origin of Sediments at the Opportunity Landing Site on Mars."

"Layered sequences observed elsewhere on heavily cratered Mars and attributed to wind, water or volcanism may well have formed similarly."


Impact base surges form meandering rivers, oxbow lakes, deltas with distributaries and inverted valleys? blink.gif blink.gif blink.gif

tty
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Bill Harris
post Dec 24 2005, 12:24 AM
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Looking at this data on a day-to-day basis we (here at UMSF) tend to kick around some strange explanations of what we are seeing on Mars. But this is normal brain-storming; with this normal winnowing process the chaff is blown away and we end up with a reasonable description. But if you devise odd alternative explanations it's not always wise to etch these in stone in case they are mis-proclamations. Some of what they are claiming is, uh, almost, uh, culinary...

--Bill


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nprev
post Dec 24 2005, 01:28 AM
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QUOTE (tty @ Dec 23 2005, 10:43 AM)
Imagine that all Earth's water froze out at the poles just 200 million years ago. Something like 75% of Earths surface would be covered by fresh, unaltered volcanics by now (=all ocean bottoms, Deccan, Ethiopia, Snake River/Columbia plateaus, Iceland, Ontong Java plateau, Kerguelen plateau, CAMP etc etc).
This despite the fact that most of the Earth's surface would have been covered by water, and all of it modified by water for the first 95% of its history.

If there was water on Mars only pre-3,5 bya I think the odd thing is that so many traces still remain.

tty
*



The "patchy" nature of Mars' surface with respect to evidence of hydrological alteration argues for comparatively brief, somewhat localized wet periods, but not as brief as impact-induced events; Meridiani's geology alone provides ample evidence of that. Regional vulcanism augmented by the greenhouse/dust-storm loop I mentioned in a previous post seems to offer a little more flexibility for both duration and location.

One fundamental attribution error that may be occurring right now in this debate is the assumption of extremes: Mars either had to be globally "wet" or globally dry. There are undoubtedly a number of situational contingencies yet to be considered that, when understood systemically, explain the observations. Mars may be a dynamically simple place in comparison to Earth, but we've already seen a bewildering variety of local variation in landforms that hints at underlying complexity in the planet's geological and climatological histories.


EDIT: corrected HTML tag errors.


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CosmicRocker
post Dec 24 2005, 05:11 AM
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I'm trying to keep an open mind, but it sure seems difficult to explain _all_ of the evidence for water on Mars with these basal surges, even if they can make thin layers with sedimentary structures. But it is true that only the MER team has all of the MER data. What they have released has been pretty convincing for me, though.

But the people who wrote these new papers are good scientists, too. I can't imagine they would risk making fools of themselves unless they thought they had a good story to tell. They did manage to publish in Nature, and that is still one of _the_ premier places to have your paper published. This is the scientific process taking place, regardless of the fact that the various news media are distorting the story.

Steve Squyres has another brief update up today, and among other interesting things, he has a comment on this debate.

http://athena1.cornell.edu/news/mubss/


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Guest_paulanderson_*
post Dec 24 2005, 05:28 AM
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QUOTE (CosmicRocker @ Dec 23 2005, 09:11 PM)
But the people who wrote these new papers are good scientists, too.  I can't imagine they would risk making fools of themselves unless they thought they had a good story to tell.  They did manage to publish in Nature, and that is still one of _the_ premier places  to have your paper published.  This is the scientific process taking place, regardless of the fact that the various news media are distorting the story.

It's interesting also that the new phyllosilicates abstract from the OMEGA team that I linked to in post #23 is in Nature as well, which gives it seemingly good credibility. In his e-mail today, McCollom also dismissed those same phyllosilicates findings... he did make a good point though, that clays can also form in hydrothermal environments, even acidic. But don't they usually form in less harsh conditions (as OMEGA has stated)? Can any of the geologists here elaborate on this a bit? I'm not a geologist, but I am a serious researcher (I was doing astronomy / space talks as early as grade 4 even - weird kid...). blink.gif
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CosmicRocker
post Dec 24 2005, 05:41 AM
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Oh man, I'm way behind on the clay stuff. Thanks for the reminder. Gotta get that paper and add it to the pile.


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Guest_BruceMoomaw_*
post Dec 24 2005, 08:11 AM
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The important thing to keep in mind is that ALL the chemical evidence of exposure to non-acid liquid water goes all the way back to the Noachian, which is a long, long time ago -- 3.8 billion years at the latest. Since then, there were occasional gigantic surface discharges of non-acid water during the Hesperian, and there are occasional fair-sized ones (mostly driven by local volcanic heating) to this day -- but they all freeze into solid ice, and then sublimate directly away into the thin atmosphere, so fast that they don't have time to chemically modify the silicate lava rocks which they come into contact with. The OMEGA team has emphasized exactly this in its reports.

Frankly, I'm starting to think that MER-A's studies in the Columbia Hills may end up being more scientifically valuable on balance than MER-B's studies of Meridiani. The latter was a single unusual, highly specialized phenomenon, of a type whose environment was likely to be unfriendly to life (or at least to its initial creation) -- but what we're seeing in the Hills seems to be a smorgasbord of surface materials from all sorts of different places on Noachian Mars, all thrown into the Hills by giant impacts and, as a total, far more representative than Meridiani of what Noachian Mars was actually like. (Including those probable clays in the "Independence" outcrops, which may are likely to have been created at the Hills themselves by exposure to regular water.)
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