| Term: | Mars |
| Definition: |
Fourth planet from Sun and the seventh largest. Mass 6.42 x 10^26 g (0.11 Earth's); radius 3397 km. Mean distance from Sun 1.52 AU. Sidereal period 687 days; synodic period 779.9 days. Surface temperature 248 K., rotational period 24h 37m 22.66s. Obliquity 23°59'. Atmosphere more than 90% CO_2, traces of O_2, CO, H_{2}O. Two tiny satellites (Phobos and Deimos), both of which are locked in synchronous rotation with Mars. |