Researchers had suspected a moon of Jupiter called Ganymede had an ocean. Now they’ve confirmed it.
Ganymede is bigger than our own moon, and even bigger than the smallest planet, Mercury. Ganymede has a magnetic field that creates northern and southern lights around its poles.
Scientists saw patterns of movement that showed the moon’s magnetic field is being influenced by a vast, salty ocean buried beneath miles of ice.
http://www.npr.org/blogs/thetwo-way/2015/03/12/392583244/moon-river-no-its-an-ocean-on-one-of-jupiters-moons