Like Earth, Mars has seasonal polar caps that grow in the winter and retreat in the spring, but on Mars the seasonal caps are composed primarily of carbon dioxide (dry ice). Carbon dioxide is the major component of the Martian atmosphere, and a significant fraction of the mass of the atmosphere is cycled through the seasonal caps every year.

This image shows sand dunes that are mostly covered by seasonal frost/ice in the northern spring. When the springtime sun shines on the ice, some of it penetrates to the base of the ice and warms the dark sand dune surface below. The warm sand evaporates the carbon dioxide ice from below, building gas pressure that apparently breaks the ice and carries sand to the surface as the pressure is released. The sand then cascades down the surface of the ice, forming the streaks seen in this image.

Written by: Ken Herkenhoff   (5 May 2010)