On Mars, the stuff we know as "dry ice," or frozen carbon dioxide, is a powerful agent for change. In winter, it forms a polar ice cap. In spring, it becomes an expanding gas that carves channels in the surface and sends loose debris into landslides.
Shown here is some of the spectacular scenery created by carbon dioxide as it freezes and thaws on Mars. From left to right, sun-warmed blocks of icy debris tumble down the cliffs of the north polar ice cap. Dust devils leave tracks on defrosting dune surfaces in the southern hemisphere. Receding south polar ice erodes the surface into scalloped ridges. During northern spring, sun-facing dunes emerge from a blanket of frost. As sunlight penetrates translucent ice near the south pole, the ice turns to gas that expands and erodes radiating channels. Where there's a break in the ice, the gas bursts forth, lofting surface materials downwind.
High Resolution Imaging Science Experiment, Mars Reconnaissance Orbiter
Image credits: NASA/JPL-Caltech/University of Arizona