A graduate student on my shuttle bus to the conference center tipped me off to a couple of really cool abstracts, presented on Tuesday and tomorrow. I was all set to push for a story about them. But then a) the authors didn’t want to talk to me about it, because they’re hoping the work will make a splash in a journal-which-will-not-be-named, and b) I realized that my eagle-eyed editor had, like MRO, already spotted the work, and its novelty, when the authors were presenting it at AGU in December.

But the gist of the work is worth repeating: members of the MRO HiRise team are using fresh impact craters as probes of the subsurface, and are finding ice farther south than anyone has thought possible. Pictured here are the two blue pools of ice exposed after small impacts last summer excavated craters five or six metres across and about 70 centimetres deep. (Little impacts like this happen quite often in Mars’ thin atmosphere.)

The authors watched the ice sublimate away over subsequent weeks, and used calculations from that to show that this ice is solid and nearly pure, not just a little bit of pore ice mixed in with the soil. And since these craters lie around 45 degrees north, it means that the subsurface ice that Mars Odyssey spotted (providing the raison d’etre for Phoenix) extends further south than previously thought. And it would support a global atmospheric water content that’s higher than what’s currently measured — a sign that subsurface ice on Mars might be in global retreat.

But mostly I just love the idea of using asteroid impacts as a natural, experimental probe. You can spend half a billion dollars to send a robot near Mars’ north pole to scoop away soil and expose a trench of ice. Or you can wait for asteroid impacts to do the scooping and trenching for you. Of course, you need to have spent $720 million on MRO, the equivalent of a martian spy satellite.

Image: NASA/JPL-Caltech/University of Arizona