Recent impacts on Mars exposes subsurface ice

The Mars Reconnaissance Orbiter (MRO) took these images of a 6m crater on Mars in October 2008 (left) and again in January 2009; see this press release for more details. This crater is absent from images acquired in 2007, so it must be due to a relatively recent impact. Note also the bright material in the crater that fades over time. This is to be expected if this were subsurface ice that was suddenly exposed to the surface. Water ice is not stable at the surface of Mars, and will sublimate (vaporize) over time. The MRO spacecraft has discovered several new craters where fresh ice appears to fade over time. This particular crater has a latitude of 43 degrees, which indicates that subsurface ice on Mars extends all the way from from the poles to Mars' mid-latitudes.