The Great Meridiani Debate Options

[Guest_paulanderson_*]

Acidic water or volcanoes / impacts? The debate is on! I kind of like this actually, for my birthday today (39 now, getting old)....

Updates regarding this today from Nature, CU and Space.com:

The Waters Ran Shallow
http://www.nature.com/nature/journal/v438/...e051222-10.html

Mars Region Probably Less Watery In Past Than Thought, Says Study
http://www.colorado.edu/news/releases/2005/470.html

New Studies Question Mars Water Assumptions
http://www.space.com/scienceastronomy/051221_mars_dry.html

Regardless though of whether they are correct or not regarding the acidic sulphate deposits in these scenarios, the earlier clays are still another matter...!

The Space.com article includes comments from Squyres (who it says was not contacted prior to the article being published):

"Squyres said a deeper understanding of the situation came when Opportunity examined Endurance Crater, where observations were made of 25 vertical feet of rock outcrops. Those results were published just a month ago, after the two Nature papers had been submitted. Knauth, McCollom and Hynek "hadn't seen that stuff when they wrote their papers," Squyres said. The nature of the layering and grain sizes deeper inside Endurance Crater "is absolutely incompatible with a volcanic or impact origin," Squyres said. It is "completely compatible" with the idea of windblown material, and the upper meter or so "shows evidence for deposition of water. The chemistry varies with depth in a way that requires that subsurface liquid water interacted with the rocks after they were deposited." Squyres emphasized that his team has always thought the water was mostly underground, occasionally creating small surface lakes that evaporated quickly. Squyres also stressed that nobody has done anything other than good science with the data available. "It's always good to have alternative hypotheses," he said. "In the end, the best ideas win. It forces everybody to go back and sharpen their arguments. All of this is a good thing."

[tty]

Volcanic ash layers I might believe in. But they would have to be very altered to lock like the Meridiani rocks.

An impact origin is ridiculous. The only way an impact can result in a thin layer of fine materials is through distant fallout of fines ejected from the crater. Having tens of meters of such thin layers but no thicker layers with coarse material requires that there were lots and lots of impacts far away but not a single one near Meridiani. And all those impacts would have to be both BIG and very far away since the laminae are thicker than e. g. the Chicxulub impact layer.

tty

[sranderson]

Odd that people are still wondering if there was ever flowing water on Mars. I would think that that one orbital image of the interleaved "fossilized" channels in a clear outflow delta would leave no doubt.

And once you concede that there was water on Mars at one time in some places, water action becomes the simplest explanation for much of what we have seen in Meridiani. Other explanations seem contrived at best.

Scott

[Guest_BruceMoomaw_*]

I've been engaged in an E-mail exchange with Brian Hynek for some time -- and I'm still trying to get a straight answer out of him as to why he thinks that the sulfuric acid to which the original Meridiani ash or sand was exposed had to be in the form of steam rather than cool liquid. More news when I get it.

[CosmicRocker]

AlexBlackwell started a similar thread in the Mars topic, but this is where the action seems to be.

I couldn't believe the hype on these new Nature articles that exploded in the news media today. When I checked my web page collage of science news this morning I found three or four links to various articles from normally trustworthy sources claiming that the Mars scientists had screwed up, and that liquid water was not needed to explain the observations of the rovers.

I am waiting for someone to send me copies of those articles, but in the mean time I have been making a mental list of observations that would support one or the other of the various hypotheses (surface water/groundwater and wind, volcanics, or impacts), and I have a difficult time buying into the new hypotheses.

You folks have already pointed out a lot of the problems with the new hypotheses, and we can elaborate on them later. But I agree, they do appear to be "contrived," or at least based on limited data. Yeah, I can imagine some special conditions like a "ground-hugging turbulent flow of rock fragments, salts, sulfides, brines and ice, leaving deposits that were later weathered by small amounts of water embedded in the grains." But is that the most simple explanation of the MER observations? Does it make sense to imagine such things when images of the planet's surface from orbiters show so many examples of fluid flow shaping the geomorphology of Mars? I think not.

As usual, I think SS said it best in that space.com article. The observations seem clear, but debate is healthy for good science. This will be a fun debate to follow...

[nprev]

I agree that it's both interesting and positive for alternative hypotheses to be considered, precisely because such debate forces everyone to re-examine both the evidence and their own assumptions.

For example, SRAnderson points out the numerous eroded (apparent! ) outflow deltas. Given their generally presumed age of 3.5By or so, is this consistent with any erosional models that might have been developed based on the results of MGS and subsequent missions? Surely we must have some basic feel for at least the steady-state wind erosion rate on Mars by now; in fact, it seems that latitiude and topologically-induced micro-climates may play at least as significant role in local surface conditions as they do on Earth.

The point of that thought is that this comparison might provide some constraints on what are essentially catastrophic formation theories for Martian sedimentary deposits. In my opinion, the highly structured (low entropy?) appearance of the Meridiani formations combined with the very regular layer spacing strongly suggests a periodic series of climatogical variations rather than ad hoc eruptions as the mechanism responsible for the terrain's formation. Whether the medium responsible for deposition was wind or water is still an open question, although it's probably a bit of both...

[nprev]

...and on that last note, what do you think of periods of high local humidity followed by dust storms that cause layers of thin mud to s-l-o-w-l-y build up at Meridiani? Actual standing surface water may not have been necessary; I wonder just how much relative humidity in that atmosphere would be enough to cause all that exceedingly fine dust to stick together...

[Guest_paulanderson_*]

And once you concede that there was water on Mars at one time in some places, water action becomes the simplest explanation for much of what we have seen in Meridiani.  Other explanations seem contrived at best.

Contrived is a good word for it. I was glad to see Space.com at least update their original story to include Squyres' comments.

Jon Clarke has provided a good listing of features more consistent with groundwater / salt lakes than volcanoes or impacts (hope you don't mind the link, Jon):

http://uplink.space.com/showthreaded.php?C...d&sb=5&o=0&vc=1

[Guest_Sunspot_*]

Take a look at spacetoday.net, this new theory is popping up everywhere in the press and being taken as fact now.

[edstrick]

The sulfate enriched and altered rocks and the sulfate cemented sandstone at Gusev are the sorts of things I'd expect from the impact scenario. The volcanism scenario utterly lacks a volcano or volcanos that would have deposited massive layered deposits over an area bigger than Oklahoma. I consider both hypotheses dead-in-the-water.

[abalone]

http://www.spaceflightnow.com/news/n0512/21marswater/

Is the dream of a shallow sea finally over?

[dvandorn]

There has been a definite "movement" out there, ever since 1971 and the Mariner 9 testament, of some people who want to find some way (ANY way) to explain the obvious fluvial features in such a way that does not require there to have ever been liquid water on the surface of Mars.

Why? Mostly, I think, because liquid water cannot exist there *now*. To accept the validity of the features as fluvial, you *must* accept the concept of a severe climate change having occurred on Mars.

Whereas, to accept them as non-fluvial, you *must* accept that some Mars-specific process creates features that *look* fluvial, but thata ctually are not.

That's why some people keep barking up the no-water alley. Because, either way you look at it, you have to accept the postulate that something happened on Mars that we cannot easily explain, or understand.

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

[Bill Harris]

Ah, the side-road of the brine-splat speculation.

Although alternate theories can be stretched to fit the observed data on Mars, the most comfortable fit is the warmer, wetter Mars. Maybe not to the extent of vast tepid inland seas, but certainly more so than the high arctic desert we see today.

--Bill

[Guest_paulanderson_*]

Take a look at spacetoday.net, this new theory is popping up everywhere in the press and being taken as fact now.

I knew this would happen... and most do not even bother to get Squyres' input. I'm glad Space.com did though. And I like Squyres' comments in today's Rocky Mountain News:

"But the lead scientist on the Mars Exploration Rover (MER) mission dismissed the CU idea as misguided and uninformed. Cornell University's Steve Squyres said the Boulder scientists did not have access to reams of recent Opportunity data, all of which "really solidify the case that water was involved in a very substantial way at this place."

http://www.rockymountainnews.com/drmn/loca...4334345,00.html

[CosmicRocker]

I just got the publications today, but I haven't had a chance to read them yet. But it really is nuts how the press has picked up this ball and ran with it. They have no idea what they are talking about, but it's controversial, and it might sell a few more papers.