Mars, rotating during a Martian day. Mars's rotation on its axis with respect to the stars (the sidereal period) takes 24 hours, 37 minutes and 22 seconds. Mars, named after the Roman god of war, is the fourth planet from the Sun. Mars's diameter is around 6780 kilometres. The iron oxide on its surface gives it a reddish appearance. Mars is a rocky desert world with a gravity about one third of that on Earth. The atmosphere is mostly carbon dioxide and surface temperatures are well below freezing.