Jupiter's Satellites
Jupiter has 16 known satellites, the four large Galilean moons and 12 small ones.
- Jupiter is very gradually slowing down due to the tidal drag produced by the Galilean satellites. Also, the same tidal forces are changing the orbits of the moons, very slowly forcing them farther from Jupiter.
- Io, Europa and Ganymede are locked together by tidal forces into a 1:2:4 orbital resonance and their orbits evolve together. Callisto is almost part of this as well. In a few hundred million years, Callisto will be locked in too, orbiting at exactly twice the period of Ganymede and eight times the period of Io.
Resonance
A state in which one orbiting object
is subject to periodic gravitational
perturbations by another