Pluto's iconic icy heart is likely harboring a slushy ocean with layers of frozen nitrogen and water ice, which best explains the features revealed after the New Horizons spacecraft flyby, a new study suggests.

What's more, the dwarf planet may have once been walloped by a large comet that left a "giant scar" on its surface, which has since then been filled with heavy nitrogen ice, scientists said.

Pluto Is An 'Ocean World'

The theory that Pluto holds an underground liquid water ocean is nothing new. In fact, a report in late September proposed that an asteroid impact may have created the dwarf planet's heart-shaped feature, hinting that it likely hides a subsurface ocean.

Now, the new research provides supporting evidence and the most detailed investigation yet of how the subsurface ocean affected the evolution of Pluto's key features, including the Sputnik Planitia.

The vast and lowland region known as Sputnik Planitia covers one side of the dwarf planet's iconic icy heart. Researchers have wondered why this 621-mile (1,000 km) deep impact basin was situated in its current location near the equator, suspiciously aligned with the dwarf planet's tidal axis.

During a computer analysis of Pluto's orbit and features, planetary scientists from University of California Santa Cruz discovered an anomaly: with the way that Pluto interacted with one of its moons Charon, more material or extra mass should be found at Sputnik Planitia.

Professor Francis Nimmo, one of the researchers of the study, described Spuntik Planitia as a big and elliptical hole, with which an extra mass must be lying underneath.

"[A]n ocean is a natural way to get that," said Nimmo.

Pluto's tides with Charon can't be explained if the dwarf planet was frozen solid all the way through. What best accounts for the extra mass is a hidden, subsurface ocean.

According to the report, the dwarf planet's slushy ocean lies about 93 to 124 miles (150 to 200 km) underneath its surface, containing a blend of ammonia, alcohol and other antifreeze chemicals.

Nimmo said Pluto holds enough rock for heat to be generated, adding that a hundred-mile thick ice shell can be quite a good insulator.

"A deep subsurface ocean is not too surprising, especially if the ocean contains ammonia, which acts like an antifreeze," he added.

Giant Scar On Pluto's Icy Heart

Similar to other planetary basins, Pluto's Sputnik Planitia may have been formed after a massive meteorite impacted the dwarf planet, which blasted away a large amount of its crust and left a giant scar. This catastrophe may have occurred within the past 4 billion years, scientists said.

Nimmo said because water is denser than ice, this scenario would leave a basin with a thin crust of ice over an upwelled mass of water. However, he said at this point they figured that no extra mass on Sputnik Planitia exists.

What happens is that the ice shell becomes strong and cold, and the impact basin becomes filled with nitrogen ice, which is the excess weight, he said.

Details of the new study were published in the journal Nature on Nov. 16.

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