Fobos

Phobos is one of Mars' two moons, notable for its irregular, potato-like shape and proximity to the planet—it's the closest moon to a planet in the solar system. It orbits Mars rapidly, completing an orbit in just about 7.7 hours. Phobos is very small, about 22 kilometers across, and is thought to be a captured asteroid or space debris. Its surface is heavily cratered, with a prominent impact crater called Stickney. Due to its rapid orbit and low altitude, Phobos appears to rise and set in about 40 minutes from the Martian surface.