Orbital Resonance is also the title of a science fiction novel by John Barnes.

In celestial mechanics, orbital resonance occurs when two orbiting bodies have periods of revolution that are in a simple integer ratio so that they exert a regular gravitational influence on each other. This can stabilize the orbits and protect them from gravitational perturbation. For instance:

• Pluto and some smaller bodies called Plutinos were saved from ejection by a 3:2 resonance with Neptune.
• The Trojan asteroids may be regarded as being protected by a 1:1 resonance with Jupiter.
• The extrasolar planets Gliese 876b and Gliese 876c are in a 2:1 orbital resonance

Orbital resonance can also destabilize one of the orbits. For instance:

• There is a series of almost empty lanes in the asteroid belt called Kirkwood gaps where the asteroids would be in resonance with Jupiter.

A Laplace resonance occurs when three or more orbiting bodies have a simple integer ratio between their orbital periods. For example, Jupiter's moons Ganymede, Europa, and Io are in a 1:2:4 orbital resonance.

See also

• Lagrangian points
• Tidal locking