Run! Hide! Cannibal Planets!
According to Dr. Robin Canup of the Southwest Research Institute and her colleagues, the four giant “Galilean” moons orbiting Jupiter are the only survivors of what the KAMS Blog likes to think of as a “moon massacre.” Earlier in the history of the solar system, there were as many as 20 moons orbiting Jupiter, but these moons were “eaten” by the planet. Canup also speculates that something similar could have happened in the case of Saturn. For further information, see here.