There is a small amount of water vapour which condenses in some places to give thin clouds and fog. There are polar caps at each pole which grow in the Martian winters, with the addition of deposits of solid carbon dioxide, and decrease in the Martian summers to leave what is thought to be a small residue of ordinary water ice. The maps were made by the orbiting Mars Global Surveyor spacecraft, using its laser altimeter instrument. The surface of Mars shows impact craters, like the Moon, mountains, rift valleys, ridges, hills plains and extinct volcanoes. There are signs that water existed on the surface at some earlier stage of the planet.
Winds can be very severe and are responsible for extensive weathering of the rocks on the surface.
Sometimes the winds blow up enormous sandstorms that obscure the view of the planet's surface. Although it is only 6794 km in diameter it is probably the most Earthlike of all the planets. There are some suggestions that it might be possible to alter the planet's atmosphere sufficiently to enable a permanent base to be set up there. Until that is done Mars will represent a very hostile environment for any human visitor. Mars has two moons, Phobos and Deimos.