Mars, computer artwork. Mars is a cold, rocky, desert world, with an atmosphere of mostly carbon dioxide. Its diameter (6800 kilometres) is around half Earth's, and its surface area is about the same as Earth's land surface area. Ices of carbon dioxide and water (white) form at the poles (North Pole at upper right). The orange colour is due to the iron oxides in the rocks. Mars orbits the Sun at an average distance of 230 million kilometres. This view shows the southern highlands, which are heavily cratered, in contrast to the much smoother and therefore younger northern hemisphere.