Pluto's heart-shaped feature hints at subsurface ocean

New research by astronomers suggests that 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.

The cutaway image of Pluto shown here is a section through the area of Sputnik Planitia, with dark blue representing a subsurface ocean and light blue for the frozen crust.

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. y NASA's New Horizons spacecraft's observations, which flew by Pluto last year, also 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 said to be the strongest.

If Pluto does have an ocean, how has it managed to avoid freezing up entirely over the past 4.5 billion years? Pluto is big enough that it may have retained a substantial amount of internal heat, Nimmo said. And the dwarf planet's water may contain significant amounts of ammonia or other substances that act as an antifreeze, he added.

Astronomers think subsurface oceans exist on the Saturn moons Enceladus and Titan; the Jovian satellites Europa, Ganymede and Callisto; and a number of other solar system bodies. Such buried water may be abundant in the Kuiper Belt, the ring of frigid objects beyond Neptune's orbit.

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Photo credit: Pam Engebretson