The origins of Sputnik Planitia, a 1,000-kilometre-wide basin within the heart-shaped region observed on Pluto’s surface, are described in two separate studies published online in Nature this week. The studies suggest that as this basin filled with ice, it made the dwarf planet roll over, creating cracks and tensions in the crust that point towards the presence of a subsurface ocean.

James Keane and co-authors propose that the current location of Sputnik Planitia was determined by tidal forces. They posit that as the basin filled with ice, it altered the tidal interactions between Pluto and Charon, causing reorientation of the dwarf planet. Their models show that this reorientation put stress on the crust, producing a network of faults that created canyons and mountains.

Francis Nimmo and colleagues also consider the implications of Pluto’s apparent reorientation. They agree that tidal forces could explain the current location of Sputnik Planitia, but suggest that these processes would require the presence of an ocean beneath Pluto’s surface.

Together, these studies provide new insights into what shaped Pluto’s heart, and how it shaped the dwarf planet.