Martian dust devils, artwork. Mars is a rocky desert world with no surface water. Wind erosion creates sandy deserts, and thermal heating creates localized vortices that can spin dust up into the atmosphere, a phenomenon called a dust devil. Dust storms can sometimes cover the whole planet. The rocks' orange colour is due to a high content of iron oxides. The Martian atmosphere, less dense than Earth's, is mostly carbon dioxide. Surface temperatures are well below freezing. The gravity is about one third of that on Earth.