Phobos is the larger of the two moons and is only 27 kilometres in diameter. This is about as far as a car can travel on the highway in 15 minutes. It is covered with craters, as Earth's moon is.
Phobos is trapped in tidal drag, with its orbit lowering roughly 1.8 meters per century. In about 50 million years, Phobos will reach the Roche limit, where it is likely to be torn apart. Some fragments will fall on Mars and some will form a planetary ring or rings around Mars.
Flights to Phobos
None. Photographs from vehicles in Mars Orbit and flybys (Viking 1, ect)
- Future Flight – Phobos-Grunt (Orbiter Addon)