The heart of Pluto is forever facing away from its largest moon, Charon. To explain why is not a story of spurned love, although it does involve a heavy heart. If the basin continues to gain mass, Pluto will continue rolling. New Horizons detected a glacier of nitrogen ice, which is also denser than water ice, covering Sputnik Planitia. Mr. Keane does not argue against an ocean, but he said a thick layer of nitrogen ice might be sufficient explanation.

Source: New York Times November 16, 2016 18:00 UTC