Moons of the Solar System: Phobos and Deimos

Mars’s moons as irregular and one of them is on its way to crashing into the planet

Mars’s two moons are called Phobos and Deimos, meaning fear and terror respectively. Mars itself is named for the Roman God of War. Phobos and Deimos were the two sons who would accompany Mars’s Greek equivalent, Ares, to war.

The two moons were discovered within six days of each other by American astronomer Asaph Hall in 1877. Both moons are irregular in shape and seem to be captured asteroids.

Simulated image of Phobos and Deimos (R) against the background of Mars. Image: Brown University

Phobos orbits Mars closer than any other moon orbits its planet. In fact, Phobos is so close to Mars, it orbits quicker than Mars rotates! So from Mars, Phobos rises and sets in just a little over four hours. The moon is gravitationally very weak, but manages to hold together its own structure at the edge of collapse. Its orbit is decaying, which means that in about 40 million years, it would crash into Mars.

Deimos orbits higher than Phobos and is about half as small. It is so small that when fully illuminated (“full moon”), viewed with naked eye from Mars, it would appear just as bright as Venus does to us today.

There are several missions being planned to explore Phobos and Deimos, considering we now know more about Mars’s surface than our own oceans. No mission has been announced yet.

Check out the entire series on other moons in our solar system.

Did you enjoy this article? Please recommend it to others by clicking on the ❤ below. You can also subscribe to our newsletter to stay updated on our Moon mission.