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Roche's limit[′rō·shəz ‚lim·ət]
the critical distance from a planet inside which, because of the destructive action of gravitational forces, satellites cannot exist. Roche’s limit was investigated by the French astronomer E. Roche (1820–83), who established that for fluid satellites this limit is A = 2.5R, where R is the radius of the planet. Since Saturn’s rings lie within Roche’s limit (the radius of the outer edge of the outer ring is equal to 2.3 times the planet’s equatorial radius), Roche concluded that the rings consist of small solid particles (1848). This was later confirmed by other investigators.
The action of gravitional forces on a solid satellite was studied by H. Jeffreys (1947), who ascertained that the internal stresses necessary to break up a solid satellite can arise only when the dimensions of the satellite are large. Thus, for a solid satellite approaching the surface of Jupiter to break up, the satellite’s diameter must be at least 400–500 km.
G. A. CHEBOTAREV