Mars. Computer artwork of the surface of Mars from multiple aspects as it rotates over six hours. North is at top. Mars is the fourth planet from the Sun, and is a rocky desert world. Its diameter is around half that of Earth's, and the surface area is about the same as Earth's land surface area. It has a thin carbon dioxide atmosphere, which forms ice at the poles. There are large canyons, volcanoes and craters on Mars. The orange colour is due to the iron oxides in the rocks.