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