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tidal force
1. The minimum distance to which a large satellite can approach its primary body without being torn apart by tidal forces.

If the satellite and primary body are of similar composition, the theoretical limit is about two and a half 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 Édouard Roche (1820–83). Artificial satellites are too small to develop substantial tidal stresses.

2. The force arising from differences in the strength of gravity experienced over different parts of an object.

Such a force is responsible for the tides, and for the breakup of a body straying within the Roche limit of a planet.

When comets pass close to a massive body like the sun or Jupiter, they may break up due, at least in part, to the tidal forces encountered.

This entry is located in the following unit: Astronomy and related astronomical terms (page 26)