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New Evidence Strengthens the Case for Pluto’s Underground Ocean

Features on the dwarf planet’s smooth surface suggest that not all is frozen on that tiny, distant world

A view of twilight on Pluto (NASA/JHU APL/SwRI)
smithsonian.com

From far in the chilly depths of our solar system, the dwarf planet Pluto keeps scientists on their toes—from its exotic ices to its chilly heart. Now, new computer modeling supports that idea that the tiny world harbors a liquid ocean between it's rocky core and outer shell of ice.

Ever since the New Horizon's Probe swung by Pluto last year, scientists have wondered if a liquid ocean could be "sloshing around under its icy crust," writes Kevin Stacey in a press release. But a new study, published in Geophysical Research Letters, suggests that this ocean is indeed a reality.

The team of Brown University researchers used computer simulations to show that if the global liquid ocean had solidified, the heavy outer ice shell would have crushed the freezing ocean into a strange type of ice called ice-II. Unlike typical ice, which expands as it freezes, ice-II takes up less volume than liquid water. As a result, the entire dwarf planet would have shrunk, causing the surface shell to buckle and scrunch up in distinctive ways, "like the skin of an overripe peach wrinkling as it dries," writes Conor Gearin for New Scientist.

Instead, the New Horizon's probe recorded deep cracks marking Pluto's surface. That leads researchers to conclude that something, perhaps heat radiating from radioactive elements in the dwarf planet's core, is keeping the ocean on Pluto wet.

That's an exciting finding because it means that other bodies in the solar system could still hold liquid water and potentially life, Ker Than reported for Smithsonian.com in January, when scientists presented the prospects for an underground ocean at a meeting of the American Geophysical Union.

"The fact that even cold, distant Pluto could have a subsurface ocean means that there are potential habitats even in apparently unpromising locations," Francis Nimmo, a New Horizons scientist based at the University of California, Santa Cruz, told Than.

Even Pluto's moon Charon could have a liquid water ocean, according to a NASA press release

Than writes:

"Such distant oceans would be very different from what we're accustomed to on Earth, notes Nadine Barlow, an astronomer at Northern Arizona University. Besides being locked beneath dozens of feet of ice, a Plutonian ocean would almost certainly have a different composition than Earth's seas.

"We have to remember that the ices out at Pluto not only include water ice but also carbon dioxide and methane ices," says Barlow. Compared to our seas, Pluto's potential ocean would also likely be especially briny, rich in dissolved salts and ammonia that would help reduce its freezing point and keep it in a liquid state.

There is a small chance that the liquid ocean under Pluto's crust could have slowly frozen into normal, non ice-II ice, but the researchers think that is unlikely. When even the seemingly hostile environment of Pluto turns out to be more friendly than we suspected, it seems more possible that there might be life out there beyond Earth.

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