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Bruce Moomaw

The theory set forth by Ray Arvidson and others before the landing -- and restated by Andrew Knoll today -- is that the top-level blueberries are actually the only existing remains of the top part of that soft light-colored outcrop rock layer, which was originally much thicker.

Judging from the craters on the Meridiani surface -- a strange mixture of extremely old eroded ones and a sprinkling of very small and sharp recent ones, with nothing in between -- the outcrop rock was covered up for billions of years after being laid down, was re-exposed by the wind only a few tens of millions of years ago, and has since then been gradually eroded away, from the top down, by windblown sand from neighboring areas (presumably that dark, olivine-rich basaltic sand detected by the rover in the bottom of its landing crater, since that sand cannot possibly have been exposed to any significant amount of liquid water during its existence). The soft, light matrix rock has been completely powderized and blown away, leaving behind the harder hematite pellets as a "lag deposit". (Knoll says the original layer of the light rock could possibly have been much thicker.)

This raises the possibility that there may actually have been quite a lot of that water-soaked Meridiani-type rock on the surface of Noachian Mars -- but that it's so soft that it's completely eroded away by the wind within only a geologically short time of ever being exposed at the surface. (In this connection, I've heard a rumor that the science team for Mars Express' OMEGA near-IR mapping spectrometer announced two days ago at the LPSC conference that they have definitely confirmed that many of the deposits of light-colored layered rock on the floor of Valles Marineris, and around the valley, are also very sulfate-rich.)

While I haven't heard the following from a scientist, I imagine the explanation for the bottom of Opportunity's crater being lined with the dry basaltic sand, and having few hematite pellets, is that the small crater was formed only recently -- with a hemisphere of material being blasted out of its bowl, exposing a cross-section edge of the light rock around its perimeter. Since then a lot of the basaltic sand has blown down into the crater, but has eroded away relatively little of the light rock from its exposed vertical edge, thus liberating relatively few new hematite pellets to roll down into the bottom of the crater. (Presumably the trillions of hematite pellets sitting on the surface of the upper plain are relatively dense and resist being rolled along by the wind, so few of them have yet rolled over the crater's lip into its interior, either.)

Duncan Young

One problem with Bruce's model for the crater floor (which I much prefer to the one offered by Phil Christensen's group - that a layer of unaltered basalt underlies the Opportunity Ledge material) is the very sharp contact that MiniTES sees between the hematite rich material and the basaltic sand.

However, I think a sorting mechanism is more likely for the following reason: In Dick Morris' talk, he pointed out the jarosite within the Opportunity Ledge material most likely formed in very low pH conditions. It would be weird for unweathered olivine to exist within meters of an overlying acid bath (unless it might be an intrusion?)
Other key findings: not a trace of goethite in Eagle Crater, the basalts at Gusev came from a planet with a different mantle to the planet that produced the SNC meteorites (most likely a temporal, rather than spatial, distinction), an explicit statment that there was no evidence for a lake (yet) in Gusev by Hap McSween, and a personal finding that sitting prezle-like in the traffic zone of the most packed LPSC conference session in years is a recipe fo disconfort. Rumor of the day was that a Mr. James Cameron was ushered in to the begining of the Mars Missions section.

Neukum was memorably charged down by the section chairs after enthusiastically showing off the latest pictures from the HRCS on Mars Express for half an hour (you have 12 minutes).

Bruce Moomaw

(1) Judging from the behavior of the scientists at last year's DPS meeting, I'm surprised Neukum wasn't lynched. (By the way, are they by any chance better-dressed this year? Every planetary science conference I've attended so far looks like a homeless people's convention.)

(2) My own LPSC source also reports that there was actually a clash between the Mini-TES team and the Mossbauer team regarding Meridiani mineralogy -- the Mossbauer people reported no goethite and lots of jarosite, while the Mini-TES people reported some goethite and little jarosite. (Since it's very easy to detect goethite using a Mossbauer -- thanks to the major differences in its spectrum taken at different times of the day with different temperatures -- I imagine the Mossbauer people are probably right about it.)

(3) One website I've found ( http://www.talkorigins.org/faqs/mom/spheres.html )debunking one piece of supposed evidence for Ancient Aliens -- a bunch of small very round goethite spherules found in a mineral formation in South Africa -- reports that they are really round pyrite nodules formed by metamorphic processes in a Precambrian volcanic ash layer which had earlier been turned into bentonite clay by exposure to liquid water -- with the pyrite later being exposed to more liquid water which turned it into goethite. Goethite, in turn, when dehydrated for a long period of time, turns naturally into hematite. Sound familiar? By the way, during such a change, pyrite turns first into jarosite, which then turns into goethite -- with a lot of sulfuric acid being released during the latter change, so that pyrite tailings in abandoned mines frequently pollute the surrounding water table with acid. And while that African ash was developing its pyrite nodules, its matrix was turned into pyrophyllite (the aluminum analog of talc) -- a very soft sheet silicate, like the sheet silicates which Mini-TES (again according to the LPSC) has probably found in the Meridiani outcrop's matrix. In short -- while there are alternative theories -- I wonder whether all those hematite berries started out as pyrite berries.

Oliver Morton

Re Bruce's 1), above. If Neukum wants to show more pictures, wouldn't posting them on his website be a good start...?

Duncan Young

Well, most of the ones he showed can be found right here (link below).
I think at LPSC he was mainly bragging (justifiably - those images are sweet!). There is a good chance of global coverage with the extended mission, and people working with them are ecstatic. Of course, once the radar sounder starts up, the pictures will start drying up (the Martian ionosphere will interfere with day time observations with the sounder, so periapsis will be moved to the night side).



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