planet

Laplace resonance

A special three-body orbital resonance, named for Jupiter's inner moons Io, Europa, and Ganymede, locked in a 4:2:1 rhythm - Io laps four times for Europa's two and Ganymede's one. The steadily repeating tugs keep their orbits slightly eccentric, and that is what sustains Io's ferocious volcanism. Pandora almost certainly needs a similar arrangement with sibling moons of Polyphemus.