Known as the Red Planet, for its rusted color, Mars is the 4th planet from the Sun and the outermost of the rocky planets. It orbits at an aproximate distance of 141.6 million miles from the Sun. It is roughly half of the size of the Earth. It is now a dry and barren planet. It has a surface marked by huge extinct volcanoes, large canyon systems, and rock-strewn plains. There planet also has vast dust storms. Spacecraft sent to explore its surface have found clouds and falling snow. Mars has seasons and polar ice caps, much like Earth. Mars was probably very different in the past. Evidence from orbiting space probes and planetaery rovers suggests that Mars had liquid water on its surface billions of years ago.