Mars's Moons

Mars moon montage
Montage of Mars's two moons
Credit: NASA/JPL-Caltech/GSFC/Univ. of Arizona

Mars has two moons called Phobos and Deimos. The planet Mars is named after the Roman god of war. As such the moons are called Phobos, which means 'fear' or 'panic', and Deimos, meaning 'terror' or 'dread'.

The moons were discovered in 1877, and there is still much debate about where they came from. The moons look very similar to asteroids. Many people think that they once lived in the asteroid belt and were pulled to Mars by its gravity. Others think that when Mars first formed it was surrounded by lots of objects. Most moved out to the asteroid belt, but Phobos and Deimos remained.

Phobos orbits really close to Mars, closer than any other moon in the Solar System. It is travelling so fast that if orbits the planet three times each day! It is also very small. It reflects very little light from the Sun, so it does not appear very bright in the sky.

Deimos orbits Mars much further away than Phobos. It is slightly smaller than the other moon, making it very faint in the sky. It is made from similar materials to other asteroids, carbon rocks and ice. It is much less cratered on the surface though, meaning it has been hit by space debris less often.

Just like Earth's Moon, both of Mars's moons always show the same side to the planet.