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takyon writes:

Pluto may have a massive subsurface ocean under its heart-shaped region, Sputnik Planitia, aligned with Pluto's tidally-locked satellite Charon:

Pluto may harbour a slushy water ocean beneath its most prominent surface feature, known as the "heart". This could explain why part of the heart-shaped region - called Sputnik Planitia - is locked in alignment with Pluto's largest moon Charon. A viscous ocean beneath the icy crust could have acted as a heavy, irregular mass that rolled Pluto over, so that Sputnik Planitia was facing the moon.

[...] Sputnik Planitia is a circular region in the heart's left "ventricle" and is aligned almost exactly opposite Charon. In addition, Pluto and Charon are tidally locked, which results in Pluto and Charon always showing the same face to each other.

"If you were to draw a line from the centre of Pluto's moon Charon through Pluto, it would come out on the other side, almost right through Sputnik Planitia. That line is what we call the tidal axis" said James Keane, from the University of Arizona, co-author of one of a pair of papers published on the subject in Nature journal. This is strongly suggestive of a particular evolutionary course for Pluto. The researchers contend that Sputnik Planitia formed somewhere else on Pluto and then dragged the entire dwarf planet over - by as much as 60 degrees - relative to its spin axis.

Also at UCSC.

Reorientation of Sputnik Planitia implies a subsurface ocean on Pluto (DOI: 10.1038/nature20148) (DX)

Previously: New Horizons Finishes Sending 2015 Flyby Data

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