Charon's Ocean

Researchers are suggesting Pluto's largest moon, Charon, may once have had a subsurface liquid water ocean, like Saturn's Enceladus and Jupiter's Europa.  They speculate that if Charon's orbit around Pluto was once more eccentric than it is now gravitational interaction between the two bodies would have created friction within Charon, thus heat, and thus, possibly, liquid water.  That same interaction would have eventually circularized Charon's orbit, freezing the little world solid.

The New Horizons spacecraft arrives at Pluto next summer, and should provide new data about Charon.