When NASA’s New Horizons spacecraft sailed past Pluto on July 14th, 2015, it gathered a treasure trove of information regarding what used to be the 9th planet. Among the most intriguing was an odd “heart shaped” feature on Pluto’s surface which is clearly of more recent origin than what surrounds it. Now, a new study published in Nature argues that the feature is actually the clearest evidence yet that Pluto supports a large sub-surface ocean.
See related: Now Even Pluto May Harbor a Subsurface Ocean
According to the authors, the equatorial location of one lobe of the “heart,” called Sputnik Planitia, is directly aligned with Pluto’s major moon Charon, sitting on the opposite side of the planet from its moon. Pluto and Charon are actually a co-orbiting pair of worlds, rotating around a common gravitational point, with Charon being tidally locked to the larger body. In short, the best explanation for the heart, which is believed to have originated as an ice-filled impact basin, is that as a massive feature, denser than the rest of the Pluto, it gradually shifted the dwarf planet’s orientation, eventually finding its natural location as gravitational anchor.
While a second study, also in the same issue of Nature, suggests that over time the ocean froze solid, the first study’s authors believe that the easiest explanation for the smooth surface of the “heart” is that it is continually replenished by water and slush up-welling from the ocean below, creating fresh, impact-free ice as it ultimately encounters the deep cold of the thin atmosphere above.