A little over six months later, more images of the same crater showed the ice was gone, leaving only brown dirt where the frozen water had been. That, too, was exactly what the scientists believed would happen: the ice had "sublimated," turning to invisible vapor in the thin, cold Martian atmosphere.

Read more: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/09/25/MN6U19SMRH.DTL#ixzz0SGDy61RG