Dry Ice Etches Terrain
Every year seasonal carbon dioxide ice, known to us as "dry ice," covers the poles of Mars. In the south polar region this ice is translucent, allowing sunlight to pass through and warm the surface below. The ice then sublimes (evaporates) from the bottom of the ice layer, and carves channels in the surface.
The channels take on many forms. In the subimage shown here the gas from the dry ice has etched wide shallow channels. This region is relatively flat, which may be the reason these channels have a different morphology than the "spiders" seen in more hummocky terrain.