The first paper (Jerolmack et al.) in a series of papers for a special issue of JGR-Planets (Special Section - Results From the Mars Exploration Rover Opportunity Mission) has just been published online.

Preprint available here:

http://www.mit.edu/%7Edouglasj/Vital_Stati...miscellany.html

Another paper, Glotch et al., is being published today. In fact, the listing of papers for this special section has been updated, and there will be more.

EDIT: See Tim's publications page for a preprint/reprint.

Great references. Thanks guys.

"Linear deconvolution of the outcrop spectral shape suggests that it is composed primarily of Al-rich opaline silica, Mg-, Ca-, and Fe-bearing sulfates, plagioclase feldspar, nontronite, and hematite."

That is the wonderfully interesting part.

Thanks, Alex.

--Bill

Super paper packed with lots of great information...a quick read leaves me with some questions and ideas:

1) the mineralogy of the light-toned outcrop suggests an origin as the weathering product of olivine-rich basalt...could the precursor unit have been the eolian-reworked basaltic sand that is stratigraphically below the light-toned sulfate-rich units?...I'd think that the increased available surface area of clastic sand-sized particles, and the intrinsic porosity and permeability of unconsolidated basaltic sand would lend it self to this process

2) if so, then is the paragenetic sequence something like this:

- accumulation of basaltic sand in a sand sheet or dune field in a low lying topographic basin (see Ultreya/Eldorado on steroids...)
- hydrothermal or basin-scale fluid movement that causes a regional rise in groundwater table...the groundwater is acidic and sulfur rich
- in places, the groundwater table intersects the surface, creating ponds, lakes, and maybe an inland sea
- the acidic groundwater reacts with the basaltic sand, creating a silica, Fe, Mg rich sulfate solution
- evaporation of this solution results in the precipitation of sulfate salts, opaline silica, and jarosite in an evaporite succession within the areas of standing water
- the areas of standing water dry up, the groundwater table goes down, the evaporites are reworked by eolian processes, and unaltered, extrabasinal mineral sands blow into the basin
- the groundwater table rises again, slightly re-dissolving and cementing the reworked evaporite, slightly altering the extrabasinal minerals blown in, and precipitating hematite concretions
- the groundwater table falls, eolian processes return, and Meridiani undergoes a long period of net erosion, exposing the concretions, and creating a lag on the surface
- of course, through out these processes, rocks variously fall out of the sky and go boom (see Victoria crater...)

3) is there any indication in the analyses of the basaltic sand below the light-toned evaporite unit, or the contact between the units, that suggests alteration?

Yes, all of the above. This mineralogy no longer whispers 'wet', it yells WATER.

The interesting find to me is the Nontronite, an iron-rich smectite (clay mineral) derived from the weathering of basalt. Not only is it another mineral that relates to a wet environment, it also has a biological tie-in. Nontronite been found to be a source for iron in the metabolism of iron- and sulfate-reducing bacteria.

I'm not a big bugs-and-bunnies sort, but many early micro-organisms on Earth were likely iron- and sulfate-reducing organisms, the iron and sulfates are too much of an energy source in an anaerobic environment to ignore.

--Bill

For anyone who's interested,
I googled nontronite and found this abstract:


"Iron reduction and alteration of nontronite NAu-2 by a sulfate-reducing bacterium"

http://www.uga.edu/srel/Reprint/2778.htm

Good find, Gray. I remember that paper.

>I'd think that the increased available surface area of clastic sand-sized particles, and the intrinsic porosity and permeability of unconsolidated basaltic sand would lend it self to this process...

The weathering processes on Mars do tend to create large quantities of basalt sand: for example the Syrtis Major region has thousands of huge barchan dunes composed of black basalt sand.

>is there any indication in the analyses of the basaltic sand below the light-toned evaporite unit...

That would be the holy grail of this mission. I've done a lot of arm-waving about a "dark basal unit" under the light evaporite sequence, which would answer a lot of questions. Perhaps we'll find it in Victoria (though I doubt we'll see it, there is too much "talus" in the crater to see the bottom). That is why the next leg of this traverse ought to be to the southeast, downhill and down-section. Victoria is a beautiful crater, but photo-ops do not make science, working the outcrops does.

--Bill

A quick note of caution:

As I mentioned in the paper, the the deconvolution of the outcrop spectral shape was not ideal. We're likely missing proper sulfate endmembers--which people are presently working hard to characterize. This can have a big effect on what other minerals are used in the deconvolution. Given that, I was trying to hedge a little with the nontronite identification, as it doesn't really fit too well with the theme of an acidic weathering environment. In any case, I just wouldn't go off the deep end talking about clays at Meridiani. I am very confident however about the identification of the amorphous silica which is interesting in and of itself.

Tim

Ah, those clays are another pesky grail to kick around, no? Or possibly a windmill to tilt at...

The pitfall of breezing through a 49-page paper. You did indeed make the tentative finding of natronite and I jumped the gun supposing more than I should have. But, still, the finding of amorphous silica is a positive note.

--Bill

Just to add to my post above....Arvidson is thinking the same way:

http://www.lpi.usra.edu/meetings/sulfates2006/pdf/7043.pdf

This is an extended abstract from an upcoming conference:

http://www.lpi.usra.edu/meetings/sulfates2006/home.shtml

There are other papers, many extremely relavent to our discussion...if anyone here happens to attend, I'm sure a summary would be well received!

Those papers are a goldmine, a feast for the mind. I'm snagging as many as I can during breaks at work thru our bigger pipeline so I don't have to dribble them thru my dial-up.

--Bill

My understanding is that the Bell et al. paper, "Chromaticity of the Martian sky as observed by the Mars Exploration Rover Pancam instruments," is going to be published online tomorrow in JGR-Planets as part of the special section noted above. I've read the paper and it's pretty interesting. Non-subscribers might keep an eye on the Pancam publications page; it looks as if the team posts a few of their reprints there.

The Bell et al. paper was just published online.

As expected, the paper is now available free from the publications page.
Direct link

Wonderful! I've been wanting information on this subject for ages. Incidentally, slinted, Doug told me once that you had done some work on true colour renderings of the Martian sky. Any directions to such would be most appreciated.

http://www.lyle.org/~markoff/ has the individual frames, but they don't make sense without position. If you have MMB, you can view the color images of the sky in their proper positional context by loading up any a panorama with a "View Mode" of "Calibrated color (DC)".
But, particularly when it comes to my sky images, please beware. The images of sky only are probably the weakest point in my color processing, and often have a strange and inappropriate brightness scale and sometimes hue.

Thanks, but I think I'm quite a few know-how steps away from being able to follow the trail you suggest. Also if special software is required I'd have to ask our college computer folks first. Have you anything handy you could post directly here that illustrates the variety of observed sky colours?

I understand the Glotch and Bandfield paper will be published online tomorrow.

Q.E.D.

The real thing

Two more papers were published online today: Squyres et al. and Yen et al. Note that Golombek et al. was published last week. Check here for an up-to-date listing as more papers trickle in for this issue.

I'll just add that the Squyres et al. paper, although only 19 pages long, is a fairly good summary of the Opportunity mission up to Purgatory, and Table 2, entitled "Summary of Rover Activities From Landing to Sol 511," is a handy reference.

Those were some fairly decent abstracts. I'm impressed. ...a couple of my favorite clips...

"Loose rocks on the soil surface are rare and include both impact ejecta and meteorites." (regarding Meridiani)

"These erosion rates are 2–5 orders of magnitude lower than the slowest continental denudation rates on Earth, indicating that liquid water was not an active erosional agent." (regarding Gusev)

Good stuff...

I don't understand this...the same scaling for the surface is not appropriate? I didn't follow this thread back far enough, I guess. There was a recent look at sky colors in:

http://www.agu.org/pubs/crossref/2006.../2006JE002687.shtml

if some basic radiative transfer calculations for a sample of dust loadings would help, i could post them here (can you work with I/F or do you prefer radiance?).

I guess this is a good opportunity (no pun intended) to give a new link to this special section. AGU tweaks its website from time to time, and I believe the new link gives a more up-to-date listing of the papers.