[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

[marsbug]

The ocean is still a speculative idea. I would have thought that if heimdall or any other impact had drilled into a preserved limestone layer (as opposed to a one-off deposit) it would be a detectable band in the crater?

As the OP notes carbonates on mars seem to be found as tiny inclusions and tiny regolith grains. This sounds to me more like water condensing in pore spaces in the rock during damp periods, giving rise to carbonate grains which are then eroded out by wind action and mixed in with the soil. I don't even know if that can happen but I've never heard that carbonates need large amounts of water to form only that they need water.

For these to make up six percent of the soil it must have happened many times, (perhaps too many times to be plausable?) but if we are going to have a major sea or lake bed as our source we need a 'smoking gun' with some signs of large scale carbonate deposits.

Now for some unfounded speculation:
Could the carbonate grains even be more contempory? If water vapour can build up enough in pore spaces today to make small amounts of liquid (perhaps if the rock had the right salts included in its structure as impurities?) could carbonate grains be slowly forming today? If it occured in soil pores might that explain the TECP results; thin films of water don't form because the water is being drawn into the few soil spaces with conditions right for liquid H2O? Can osmotic pressure (dimly remebered from school) work that way?

Anyway I'd like to see a crater with a ring of carbonate or a half destroyed carbonate deposite before we decide the grains started out as one big piece. My babbling for today.....