Glaciers move, or flow, downhill due to gravity and the internal deformation of ice on Earth. It is not the same when there is dry ice (frozen carbon dioxide). NASA research indicates hunks of frozen carbon dioxide — dry ice — may glide down some Martian sand dunes on cushions of gas similar to miniature hovercraft, plowing furrows as they go. Researchers deduced this process could explain one enigmatic class of gullies seen on Martian sand dunes by examining images from NASA’s Mars Reconnaissance Orbiter (MRO) and performing experiments on sand dunes in Utah and California.