Mars. Computer artwork showing the surface of Mars. Seen here is the polar ice cap (white) of the Martian North Pole (Planum Boreum), composed mainly of frozen water and carbon dioxide. The ice cap extends up to the 80 degree latitude circle. During the local winter atmospheric carbon dioxide freezes out onto the polar terrain and creates a thin white layer covering a much greater area. The northern hemisphere is characterised by vast, sparsely cratered plains. The southern hemisphere is highly cratered and features large canyons system such as Valles Marineris. In the background is the Milky Way.