Dunes in the spring

A piece of Mars: Dunes near the north and south poles get cold in the winter, just like they do on Earth. Except on Mars instead of H2O ice, it’s a mix of CO2 and H2O ice (mostly CO2). In the spring the white ice slowly disappears, revealing the dark dunes underneath. (HiRISE PSP_002033_1325, NASA/JPL/University of Arizona)