Ganymede is the largest and most massive moon of Jupiter and in the Solar System. The ninth largest object in the Solar System, it is the largest without a substantial atmosphere. Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field. Ganymede orbits Jupiter in roughly seven days.
It was place for at least two adventures of Tommy Tomorrow.