Mars The high resolution imaging science experiment camera on Nasa’s Mars reconnaissance orbiter shows snow and ice accumulated during winter covering dunes in the northern hemisphere. Unlike on Earth, this snow and ice is carbon dioxide, better known as dry ice. When the sun starts shining on it in the spring, the ice on the smooth surface of the dune cracks and escaping gas carries dark sand out from the dune below, often creating beautiful patterns.

Photograph: NASA/AFP/Getty Images