Pluto's famous heart-shaped feature caused the dwarf planet to roll over the eons, and this reorientation probably wouldn't have been possible without a subsurface ocean, new research suggests.
The left lobe of Pluto's "heart" is a 600-mile-wide (1,000 kilometers) plain called Sputnik Planitia (formerly known as Sputnik Planum), which astronomers think is an enormous impact crater. This basin has been filling with nitrogen ice over the years and now contains huge amounts of the stuff. Indeed, observations by NASA's New Horizons spacecraft, which flew by Pluto last year, suggest that Sputnik Planitia's ice may be up to 6 miles (10 km) thick.
Sputnik Planitia is aligned nicely with Pluto's "tidal axis" — the line along which the gravitational pull from the dwarf planet's largest moon, Charon, is the strongest. And that's probably no coincidence, according to two new studies, both of which were published online today (Nov. 16) in the journal Nature