Mars is accompanied on its orbit around the Sun by two moons, Deimos and Phobos. Their names are taken from Homer's "Iliad" and mean "terror" and "fear". They have highly irregular shapes and resemble huge potatoes.
The existence of Deimos and Phobos was considered a possibility several hundred years before their actual discovery. The description of the two moons of Mars in "Gulliver's Travels" (1726) by Jonathan Swift is quite close to reality.
The moons of Mars were discovered in 1877 by Asaph Hall at the Washington Observatory. It is almost certain that they were captured from a nearby asteroid_belt. Deimos and Phobos are two small moons. The mean diameter of Deimos is only 13 kilometers, that of Phobos 25 kilometers. Both are almost completely covered with different sized craters. Deimos is made of very dark rock. Its surface is smoother and less cratered than that of Phobos. The surface of Phobos is coarser with strange furrows up to 500 meters wide. It has large craters, the largest being Stickney with a diameter of 10 kilometers.
The moons orbit Mars on very different paths. Phobos is 9270 kilometers distant from the planet. It completes one orbit in 7 hours 39 minutes. Deimos' orbit is 23,400 kilometers from Mars. The Moon has an orbit_period of 30 hours and 21 minutes.
