Object Analysis

Phobos is the larger and closer of the two natural satellites of Mars. It is a small, irregularly shaped object with a mean radius of 11 km (7 mi). It orbits Mars closer than any other moon orbits its planet in the Solar System—less than 6,000 km above the surface.

Phobos is dominated by the massive Stickney crater, which is 9 km across. The impact that created this crater nearly shattered the moon. Grooves radiating from the crater suggest structural failure during the impact event.

Because it orbits below the synchronous orbit radius, Phobos is spiraling inward at a rate of 2 meters per century. In about 30 to 50 million years, it will either crash into Mars or break apart into a planetary ring. It is essentially a doomed moon.