And there are tantalizing hints that oceans could exist on Ganymede ... an ocean seemed impossible. Mimas looks much like our Moon, with a heavily cratered surface. It didn’t host any ...

At Callisto, during 21 flybys JUICE will study its cratered surface, look for evidence of a subsurface ... be similar to Earth in some ways. “Ganymede is like a mini-planet,” said Witasse.