17 June 2006
This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a group of sand dunes, covered by seasonal carbon dioxide frost, in the martian north polar region. Over the course of northern hemisphere spring, the carbon dioxide frost sublimes away, slowly revealing the dark sand that makes up the dunes. The dark spots in this image may be patches of freshly-exposed sand, or they could be places where the CO2 frost has changed, either becoming rougher, coarser-grained (larger crystals), or both. A rougher or coarser-grained surface will appear darker because of an increase in shadowing of the surface by the small-scale roughness elements.

Location near: 75.2°N, 51.3°W
Image width: ~3 km (~1.9 mi)
Illumination from: lower left
Season: Northern Spring