The outer solar system is awash with liquid water. A briny ocean is concealed beneath the icy crust of Jupiter’s fourth largest moon, Europa — with more water than all of Earth’s oceans combined. A subsurface sea on Saturn’s moon, Enceladus, spews plumes of water vapor into space. And there are tantalizing hints that oceans could exist on Ganymede, Callisto, Titan and other distant moons, too.
