19 July 2006
This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a portion of a sand dune field in the north polar region of Mars. The dunes are covered with frozen carbon dioxide which accumulated over the autumn and winter months in the northern hemisphere. During the spring, the time at which this image was acquired, the carbon dioxide begins to sublime away, going directly from solid to gas, just as dry ice does here on Earth. The dark spots, streaked by blowing winds, may be places where the frost has been removed (exposing underlying dark sand), places where the grain size or roughness of the frost has increased (increasing shadowing due to the change in texture), or both.

Location near: 79.7°N, 148.3°W
Image width: ~3 km (~1.9 mi)
Illumination from: lower left
Season: Northern Spring