"Phobos: Doomed Moon of Mars This is Phobos, one of the two moons of Mars, and it's living on borrowed time. It is thought to be perhaps a captured asteroid, sucked in by Mars' gravity, and its pock-marked surface is scarred with craters thanks to debris ejected from its home planet's own collisions with meteors and the like over the years. But Phobos won't be around forever. Unlike our own Moon, which orbits at a safe distance of several hundred thousand kilometers (and will one day be ""tidally locked"" to Earth), Phobos is less than 6,000 km from Mars. This causes extreme tidal forces, stretching Phobos like saltwater taffy made of solid rock. Eventually, perhaps a million years from now, it will crumble into a ring of debris, with that ring later decaying into an orbital rainstorm of rocky meteoric fireballs. That's pretty cool. Mars will eat its own moon one day, in a spectacular show of orbital destruction, and I'm sorry we won't be around to watch. (via APOD)"