Red Planet Impact: Huge Moons May Have Crashed Into Mars

The moons of Mars, Phobos and Deimos, may be the only survivors of a giant impact that created many short-lived, but now-absent moons around the Red Planet, a new study finds. Phobos and Deimos are both small for moons — about 14 and 7.7 miles (22.5 and 12.4 kilometers) wide, respectively — and sort of potato-shaped. As a result, astronomers previously hypothesized that these moons were asteroids captured by Mars' gravitational pull.