The November 30, 2005, issue of the journal Earth and Planetary Science Letters, Volume 240, Issue 1, pp. 1-190, has just been published online. It is a special issue entitled "Sedimentary Geology at Meridiani Planum, Mars," edited by Steven W. Squyres and Andrew H. Knoll.

Doug, the topic line got truncated. Could you chage it to something like "EPSL (November 30, 2005)"? Thanks.

Done - these are the papers that Steve mentions in the Q'n'A - pity about the subscription requirement - I would love to read the whole damn lot of them

Doug

<cough>BugMeNot</cough>

Sadly is a fiscal subscription, not just a normal subscription - and although bugmenot had many suggestions (i gave up after 30) , none actually worked Hey ho - I have all the JGR-Planets inprints to read in Spain

Doug

Doug, give me a good email address in the "other group" and I think I might be able to add to your reading pile for Spain :-)

Thanks

At this rate, Douglas Adams Triology of Four wont even leave the suitcase

Doug

(from "Sedimentary rocks at Meridiani Planum: Origin, diagenesis, and implications for life on Mars", by Squyres and Knoll).

I note they refer only to "transient pools of surface water".

Have the MER team moved away altogether from the idea of the Meridani site being at the edge of a one-time lake or sea or is that still a possibility?

======
Stephen

Current thought is a desert-playa environment. Still, the fluctuating water table represents a large volume of water plus a mechanism to introduce the water. And remember, "transient", in geological time, can be a long time in human terms.

--Bill

Also, that description is of the area of Burns Cliff that Oppy was able to reach -- isn't that the area of the sequence *below* the main evaporite beds?

In other words, that description applies to the Meridiani area prior to its periodic inundation by a shallow sea. The desert playa formations predate the deposition of tens of meters of evaporite.

At least, that's how I read it.

-the other Doug

I don't know if it's been mentioned here previously or not; however, for those who don't have access to EPSL and the Grotzinger et al. paper, the lecture materials for John's Grotzinger's October 13, 2005, presentation "The 2004 Mars Exploration Rover Mission: Evidence for Water and Prospects for Life," are now online. See the left side under "Lecture Archives."

I think this particular interpretation became widely accepted when Opportunity saw the vertical stratigraphic sequence at Endurance Crater and after the first geochemical and geomorphological data were analyzed. In fact, even before that many in the Mars science community were skeptical of a "Meridiani Planum sea" to explain the hematite and pointed out that the regional topography really doesn't support the idea of an enclosed basin/paleosea.

I've been looking over Grotzinger's October 13th lecture Power Point presentation, on and off, since it was released some weeks ago. It's a good read. I've tried to view the archived webcast of the lecture, but have not been able to get it to replay beyond the first few introductory words. If anyone else has been successful and has any suggestions, I'd appreciate hearing them.

Regarding interpretations of the depositional and post-depositional environments that created these rocks, it appears the team developed a composite stratigraphic section based on visual observations of rock texture along the Endurance ingress route, at Burns Cliff, and probably sites in between. Thanks to some concurrent spectral measurements, they were also able to create a chemostratigraphic section that was correlated to the textural one. Together, those two sections provide a really nice basis for an initial environmental interpretation.

In the limited section observed in Endurance, several transitions were observed, but I think the most notable was the unconformity observed at Burns Cliff. I didn't know it had been named, but it's called the Wellington Contact in Grotzinger's presentation. That contact suggests an environment that changed from wind-blown dunes to wet sediments deposited in shallow water. The chemostratigrapy also supports an arid environment that led to the deposition of quite a lot of evaporite salts within the sediments.

I've "borrowed" a couple of the images from Dr. Grotzinger's Power Point file, that I think are relevant to this discussion. But I would recommend that anyone seriously interested in this stuff check out his entire presentation. It's very good and contains images of earthly analogues. Ignore the second copy of the column. I don't know where it comes from, but it is a duplicate, and I can't delete it. Other important notes about the stratigraphic column were not attached to that image. See the original PPT file to view it as the author intended.

By the way, as I recall, they did a super-res set of images of the Wellington contact when they realized they weren't going to chance going all the way across Burns cliff to get to the contact. The "borrowed" image of that contact is the best one I have seen of it. Could it be the result of the super-res stack?

Click to view attachmentClick to view attachment

Yes, this is the so-called "White Plains" model with playas, etc. that many on the Opportunity science team favor, though one of the $64,000 (or $850 million) questions is from whence the water was derived. Precipitation from the atmosphere, transient groundwater release, melting of retreating ice sheets, etc.?

EDIT (11/23/05): Oops. Change "White Plains" to "White Sands." What was I thinking?

Ahh, yes. If someone only had the details about the history of water on Mars. These intriguing glimpses provided by the two rovers in two very different geologic terrains really only give us a pair of limited windows into Martian geological history. While it is tempting to grab these new and high-resolution ground-truth samples, and then attempt to extrapolate martian history, the fact is that we do not have the boots-on-the-ground observations we need to paint a sufficiently long section of Martian geological history.

It seems that the window we are looking through might be showing the late stages of the water history and an arid environment, but the sedimentological clues of things like the festoon crossbedding indicate flowing water. You can throw in complications, like aeolian erosion down to the capillary fringe, and other intricacies, but the fact of the matter remains. We do not have enough of the fine geological observations needed to determine where Meridiani's sediments lie in the the history of water on Mars. Is this only the late stages of a previously wet, primordial planet, are we seeing only a stage in a cyclical process, or is it a transient or episodic event?

I think you hit the nail on the head. As far as we really know, it could have been any of those processes. Am I sounding evasive? I think so. Damn, you've got to love these Rovers, though.

Precisely the quandry, Tom. It's a 50% chance between three choices... We've got these jigsaw puzzle pieces spread out on the table and we can't tell if the completed puzzle is going to be a beach, a woodland or a mountain scene.

We know more that we did, and since we aren't picking out gingerbread men in these images, we're doing OK.

--Bill

I tend to think so also, Endurance hinted at a dryer period below the layers of blueberry sediments, but what is below that?

The difference between Mars and Earth in this respect is that geology are ongoing on Earth but on Mars things did run almost to a standstill with the exception for the erosion of small pebbles over a very long timespan.
There could have been cliffs and outcrops earlier, but most have been eroded only protected in sheltered locations like down in Endurance or again Victoria.



Does that suggest that you have inside information that Marvin have teamed up with Daffy making christmas preparations already?

We are getting a lot of puzzle-pieces in putting together the history of this area and we can toss around various (sometimes conflicting) explanations of what we see; however, we aren't quite Daffy about it, and we are very far from getting Goofy about it...

--Bill

November 29, 2005

George Deutsch/Erica Hupp
Headquarters, Washington
(202) 358-1324/1237

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-6278)

RELEASE: 05-415

NASA ROVER HELPS REVEAL POSSIBLE SECRETS OF MARTIAN LIFE

Life may have had a tough time getting started in the ancient
environment that left its mark in the Martian rock layers examined by
NASA's Opportunity rover. The most thorough analysis yet of the
rover's discoveries reveals the challenges life may have faced in the
harsh Martian environment.

"This is the most significant set of papers our team has published,"
said Dr. Steve Squyres of Cornell University, Ithaca, N.Y. He is
principal investigator for the science instruments on Opportunity and
its twin rover, Spirit. The lengthy reports reflect more thorough
analysis of Opportunity's findings than earlier papers.

Scientists have been able to deduce conditions in the Meridiani Planum
region of Mars were sometimes wet, strongly acidic and oxidizing.
Those conditions probably posed stiff challenges to the origin of
Martian life.

Based on Opportunity's data, nine papers by 60 researchers in volume
240, issue 1 of the journal Earth and Planetary Science Letters
discuss what this part of the Martian Meridiani Planum region was
like eons ago. The papers present comparisons to some harsh habitats
on Earth and examine the ramifications for possible life on Mars.

Dr. Andrew Knoll of Harvard University, Cambridge, Mass., a paper
co-author, said, "Life that had evolved in other places or earlier
times on Mars, if any did, might adapt to Meridiani conditions, but
the kind of chemical reactions we think were important to giving rise
to life on Earth simply could not have happened at Meridiani."

Scientists analyzed data about stacked sedimentary rock layers 23 feet
thick, exposed inside "Endurance Crater." They identified three
divisions within the stack. The lowest, oldest portion had the
signature of dry sand dunes; the middle portion, windblown sheets of
sand with all the particles produced in part by previous evaporation
of liquid water. The upper portion corresponded to layers Opportunity
found earlier inside a smaller crater near its landing site.

Materials in all three divisions were wet both before and after the
layers were deposited by either wind or water. Researchers described
chemical evidence that the sand grains deposited in the layers had
been altered by water before the layers formed. Scientists analyzed
how acidic water moving through the layers after they were in place
caused changes such as the formation of hematite-rich spherules
within the rocks.

Experimental and theoretical testing reinforces the interpretation of
changes caused by acidic water interacting with the rock layers. "We
made simulated Mars rocks in our laboratory then infused acidic
fluids through them," said researcher Nicholas Tosca from the State
University of New York. "Our theoretical model shows the minerals
predicted to form when those fluids evaporate bear a remarkable
similarity to the minerals identified in the Meridiani outcrop."

The stack of layers in Endurance Crater resulted from a changeable
environment perhaps 3.5 to 4 billion years ago. The area may have
looked like salt flats occasionally holding water, surrounded by
dunes. The White Sands region in New Mexico bears a similar physical
resemblance. "For the chemistry and mineralogy of the environment, an
acidic river basin named Rio Tinto, in Spain, provides useful
similarities," said Dr. David Fernandez-Remolar of Spain's Centro de
Astrobiologia.

Many types of microbes live in the Rio Tinto environment, one of the
reasons for concluding that ancient Meridiani could have been
habitable. However, the organisms at Rio Tinto are descended from
populations that live in less acidic and stressful habitats. If
Meridiani had any life, it might have had to originate in a different
habitat.

"You need to be very careful when you are talking about the prospect
for life on Mars," Knoll said. "We've looked at only a very small
parcel of Martian real estate. The geological record Opportunity has
examined comes from a relatively short period out of Mars' long
history."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Mars
Exploration Rover project. Images and information about the rovers
and their discoveries are available at:

http://www.nasa.gov/vision/universe/solars...m/mer_main.html


-end-