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|Roche limit |
The shortest distance at which a satellite not held together by any force other than its own gravity can orbit another celestial body without being torn apart by the tidal force between them. The distance depends on the densities of the two bodies and the orbit of the satellite. If the satellite and the object are of similar densities, the Roche limit is about two and a half times the radius of the larger object. Since most natural satellites are rigid bodies, their tensile strength allows them to orbit much closer than their Roche limit; however, rigid bodies too may be broken up by tidal forces. The rings surrounding Saturn and the other gas giants in the outer solar system may be the orbiting debris of moons that approached much closer than the Roche limit and were fragmented by tidal forces. The limit is named after the French mathematician Edouard Roche (1820-83).