Pluto's 'Hulk-like' Moon Charon: A Possible Ancient Ocean?

Explanation: Images from NASA's New Horizons mission suggest that Pluto's largest moon, Charon, once had a subsurface ocean that has long since frozen and expanded, pushing out on the moon's surface and causing it to stretch and fracture on a massive scale. Charon's outer layer is primarily water ice. When the moon was young this layer was warmed by the decay of radioactive elements, as well as Charon's own internal heat of formation. Scientists say Charon could have been warm enough to cause the water ice to melt deep down, creating a subsurface ocean. But as Charon cooled over time, this ocean would have frozen and expanded (as happens when water freezes), pushing the surface outward and producing the massive chasms we see today.

Pluto

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute