How many moons does Mars have?
Answer
Two
Mars has two moons: Phobos and Deimos. Both are small, irregularly shaped natural satellites that orbit the planet close to its equatorial plane.
American astronomer Asaph Hall discovered Deimos on August 12, 1877, and Phobos six days later at the U.S. Naval Observatory in Washington, D.C. Their names come from Greek mythology: Phobos represents fear and panic, while Deimos represents terror and dread. They were companions of Ares, the Greek counterpart of Mars.
Phobos is the larger and closer moon, measuring about 22 kilometers across and completing an orbit in roughly 7.66 hours. Deimos is about 12.6 kilometers wide and takes approximately 30.3 hours to orbit Mars. Because Phobos travels faster than Mars rotates, it appears to rise in the west and set in the east—opposite the motion of Earth's Moon.
Scientists still debate how the moons formed. They may be captured asteroids, or debris produced by an ancient impact involving Mars. Phobos is gradually spiraling inward and may eventually break apart or collide with Mars.