Roche Limit:

The Roche limit is the minimum distance to which a large satellite can approach its primary body without being torn apart by tidal forces. If satellite and primary are of similar composition, the theoretical limit is about 2 1/2 times the radius of the larger body. The rings of Saturn lie inside Saturn's Roche limit and may be the debris of a demolished moon. The limit was first calculated by the French astronomer douard Roche (1820-83). Artificial satellites are too small to develop substantial tidal stresses.

Excerpt from the Encyclopedia Britannica without permission.