- MEAN RADIUS:
- 13.4×11.2×9.2 km
- MASS: 1.063 × 1019 g
- GRAVITY: Negligible
- ORBIT PERIOD: 0.31891023 (Earth days)
- ROTATION PERIOD: Synchronous
- ECCENTRICITY OF ORBIT: 0.015
Phobos, named after a messenger of the Roman god of war, is the larger and innermost of Mars' two moons. In Greek mythology, Phobos is one of the sons of Ares (Mars) and Aphrodite (Venus). Phobos is Greek for fear, it's the root word for phobia.
It was discovered August 12, 1877 by Asaph Hall. Mariner 9 photographed it during a flyby in 1971, Viking 1 in 1977, and Phobos in 1988.
Phobos does have something to fear. It is doomed. Due to its low orbit, tidal forces are slowly lowering that orbit, currently by about 1.8 meters per century. In about 50 million years, it will either crash into its mother world, or break up into a ring. Phobos has no atmosphere. It may be a captured asteroid, but some scientists show evidence that contradicts this theory.