Asaph Hall discovered Phobos on August 12, 1877.

Phobos circles Mars under the geo-stationary orbital radius. It rises in the west and dashes quickly across the sky setting in the east. This takes place normally twice a day.

Since Phobos just barely sweeps above the surface of Mars it is not possible to observe it from all points of the surface of Mars. Because its path is situated below the synchronous height, tidal power lowers its path (approximately 1.8 m per year). In approximately 50 million years it will either collide with mars or (more probable) disintegrate into a ring.

Deimos also written Dejmos, is the smaller outer Mars moon. It is the smallest known moon in our solar system.

In Greek Mythology Deimos is also son of Ares and Aphrodite. Deimos means "panic" in Ancient Greek. It was also discovered by Asaph Hall on August 12, 1877.

Deimos and Phobos are both made up of carbon rich rock, such as type C asteroids, and ice. They are both heavily.

It is possible that both of these moons were asteroids that were pulled into orbit by Jupiter, providing the opportunity for them to be trapped by Mars. There is no satisfactory theory revealing how Deimos and Phobos came to orbit around Mars.