http://scienceblogs.com/catdynamics/2009/09/water_water_everywhere.php [Broken] Nasa press release from 24 September. http://marsprogram.jpl.nasa.gov/mro/newsroom/pressreleases/20090924a.html Photos of fresh meteorite craters show white at estimated depths of 1 - 3 meters. The white material goes away within a few weeks. It is almost certainly ice, which the small meteorite impact exposes, and which then evaporates in the course of time. Spectrograph reading confirmed it's H2O.