Mars Global Surveyor passes over the north polar polar region of the red planet twelve times each day, offering many opportunities to observe how the polar cap frosts and dunes are changing as the days go by. Right now it is summer in the north. This picture, taken the second week of April 1999, shows dark sand dunes and remnant patches of bright frost left over from the winter that ended in July 1998.
Dark streaks indicate recent movement of sand.
Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission.