The Phoenix lander has been doing all sorts of cool things since it touched down on the red planet a few months ago. And the news keeps coming down in a flurry... literally!
Phoenix has an experiment on board that beams a laser upward to measure how the atmosphere and ground interact. Incredibly, it detected snow falling from clouds! Sadly, the snow vaporized before it could get the surface, so there won't be any Marvin the Snowman antics from the Phoenix engineers. Actual falling snow has never been detected on Mars before, so this is pretty cool. Every time I hear something like that, I'm reminded that Mars is a world, an actual place, and not just a reddish-butterscotch dot in the sky. Wow.
Also, Phoenix has detected what looks to be calcium carbonate -- chalk -- in the Martian regolith. On Earth, that only happens when there is interaction with water, so this is another piece of evidence on the checklist that says that liquid water once flowed at least for a while on the surface of Mars. The evidence for calcium carbonate comes from the ovens on board the lander used to bake the regolith: as the samples were heated, carbon dioxide was detected when the temperature reached a point known to be the decomposition temperature of calcium carbonate, which is also known to release CO2 in these conditions.
I should caution conclusion-jumpers that while yes, calcium carbonate can be created on Earth by the death and compression of marine animal shells, there are plenty of non-biological processes that can generate it as well. Heck, calcium carbonate is the principle ingredient of chicken egg shells, but I think claiming that Marvin's been making omelets is a stretch too.
Anyway, as northern winter on Mars sets in, and the Phoenix mission winds down, I expect the scientists involved will be sad, but still overjoyed to have so much data with which to work. It'll be very exciting to see what else they can find!
Picture credit: Mars image from NASA/Phoenix, the snowman from Mykl Roventine's Flickr set (CC license), and the Marvin found randomly on the web with no pedigree. I made the composite, without an Earth-shattering kaboom.