Phobos Lives on Borrowed Time

...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.