These volcanoes probably released the water and carbon dioxide still found in the thin atmosphere which produces dust storms, clouds and mist. There is a thin ice cap at the poles, probably made of water ice and solid carbon dioxide. Channels on the surface indicate that liquid water once flowed on the surface of Mars. Mars has two small moons which are probably captured asteroids. It had long been thought that life might exist on Mars but satellite exploration has found no evidence for it.
Some people think they can see evidence of cells in meteorites believed to have come from Mars.