The Roche Limit [SL9] Closed

The Roche Limit was first described by Edouard Roche in 1848. It is the closest distance a body can come to a planet without being pulled apart by the planet's tidal (gravity) force. As a result, large moons cannot survive inside the Roche Limit. On July 7, 1992, Comet Shoemaker-Levy 9 broke apart into 21 pieces due to tidal forces when it passed within Jupiter's Roche Limit; on the subsequent pass, each of the comet's pieces collided with Jupiter.
If a planet and a moon have identical densities, then the Roche Limit is 2.446 times the radius of the planet. The Roche Limits for the ringed planets are:

•Jupiter - 175,000 km (108,000 miles)
•Saturn - 147,000 km ( 92,000 miles)
•Uranus - 62,000 km ( 39,000 miles)
•Neptune - 59,000 km ( 37,000 miles)
This limit represents the rough boundary between each planet's ring system and its innermost moons.