Featured VIDEO: Planet Mars

Mars is the fourth planet from the Sun. It is only about half as big as Earth and has only about one-quarter of our planet's surface area. But because Mars doesn't have any oceans or seas, the total area of the Martian surface is about equal to that of Earth's dry land. Mars has two tiny satellites, Phobos and Deimos, both believed to be captured asteroids. Mars orbits about one and half times farther from the Sun than Earth does, which is the main reason it's so much colder. The orbit of Mars is also noticeably more elliptical than Earth's. One Martian year equals just under two Earth years because Mars takes 687 days to complete an orbit. Although the yearly average temperature over the whole surface is about -55°C (-67°F), the temperature ranges from as low as -133°C (-207°F) at the winter pole to a surprisingly balmy 27°C (80°F) at the equator on a summer day. These values are generally much lower than would occur on Earth if our planet orbited the Sun at the distance of Mars, due to the relatively feeble greenhouse effect of the thin Martian atmosphere.

(For further details see Mars »)

(Source: The Internet Encyclopedia of Science »)