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 northern hemisphere is characterised by vast, sparsely cratered plains. The southern hemisphere is highly cratered and features large canyons systems such as Valles Marineris. On the right is the volcano Elysium Mons flanked by Hecates Tholus to the northeast, and Albor Tholus to the southeast.