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.

Two studies published on Wednesday by the journal Nature show how the surface of Pluto might have been scarred long ago when a smaller body slammed into it. The resulting crater then partially filled with denser nitrogen ice and possibly a bulge of liquid water from an underground ocean, and the additional mass caused Pluto to roll over, perhaps as much as 60 degrees, to its present configuration, the scientists conclude.

“These are interesting and plausible papers,” said David J. Stevenson, a professor of planetary science at the California Institute of Technology who was not involved with either paper.