Mars has two natural moons: Phobos and Deimos.
Both moons are small and irregularly shaped, unlike Earth's large, nearly spherical Moon. Their names come from Greek mythology: Phobos represents fear or panic, while Deimos represents terror or dread. They are companions of the war god Ares, the Greek counterpart of the Roman Mars.
The American astronomer Asaph Hall discovered both moons in 1877 while using the 26-inch refractor at the U.S. Naval Observatory in Washington, D.C. He found Phobos on August 17 and Deimos on August 12, although Deimos was observed first chronologically. Hall named them after figures associated with Ares in Homer's Iliad.
Phobos is the larger and closer moon, orbiting Mars so rapidly that it rises in the west and sets in the east. Deimos is smaller and farther away. Their dark, asteroid-like appearances have led to continuing debate about their origins.