[X] My Assistant

[dvandorn]

As we all know, Martian meteorite ALH84001 has interesting structures that have now been debated endlessly as to their origins. The more interesting point, however, is that these structures occur within carbonate inclusions in the rock.

Carbonate Martian rocks have generally not been found from orbit by remote sensing equipment. And in ALH84001, the carbonate "nuggets" are rather tiny inclusions.

If there *are* carbonate rocks on Mars, how the heck do we find them? And if they tend to exist merely as tiny inclusions in other rocks, how do we analyze them (or even see that they're there) in situ?

-the other Doug

[dvandorn]

We don't see this admixture of carbonates from orbit in this area. That tells me that mixing the carbonates into the regolith at this kind of level (five to six percent) effectively hides it from orbital sensing. We needed something like TEGA and the AFM, working together, to make a positive identification of carbonates in this soil. So, that answers why we don't see it elsewhere -- it can't be seen easily from orbit, and nowhere else on Mars have we landed the kind of instruments that can actually detect this level of finely ground carbonate "flakes" in the soil.

So, indeed, it's possible that all of the soils on Mars contain a similar amount of carbonate material. We simply don't have the ability to detect it with the instruments currently deployed.

On the question of how representative this soil is, and whether or not local impact events have controlled its composition, there are a lot of ways to go with that. For one thing, Mars has for some time been spoken of as having a "ubiquitous dust layer" that is pretty much homogenous in composition and character everywhere on the planet, spread over the top of every landform by the global air circulation. It's very difficult to separate the soil components at any given location that are primarily derived locally, and the components that have been blown in on the wind.

Also, the polar regions build up layer after layer of accreted dust every year; Phoenix is only a few hundred kilometers from places where alternating layers of water ice and dust are being laid down, year after Martian year. We don't have a theory that even begins to address how long these polar soils at the Phoenix site have been in situ (though the lack of smaller impact craters hints that this terrain is being renewed pretty regularly). And if these soils are being actively renewed, how much of the material we see in place right now can have been locally derived?

There are a lot of questions to answer. I think it shows that my original set of four questions has to have been a pretty good starter set, since even setting limits on the estimate ranges seems to be bringing up other really good questions.

-the other Doug