Phobos is the innermost and larger of the two natural satellites of Mars, the other being Deimos. Both moons were discovered in 1877 by American astronomer Asaph Hall. Phobos is a small, irregularly shaped object with a mean radius of 11 km and is seven times as massive as the outer moon, Deimos.

Radius: 7.0008 mi

Orbital period: 8 hours

Distance to Earth: 48.34 million mi

Gravity: 0.0057 m/s²

Surface area: 1548.3 km²; (3.03545 µEarths)

Did you know: It is believed that it will one day crash into Mars, possibly in as little as 10 million years.