Pluto’s heart is one of the most intriguing and puzzling features on the dwarf planet. Its smooth surface indicates that it is constantly changing, and researchers have toyed with the idea that there’s a liquid ocean under it.
So a US research team, led by Brandon Johnson from Brown University, constructed a new model for Pluto. They simulated the scenarios that could create the massive impact crater that is Pluto's heart, formally known as Sputnik Planum.
And they found that the presence of an ocean beneath the Plutonian surface was highly likely, suggesting it may be 100 kilometers (62 miles) thick. And the study also indicates it may be as salty as the Dead Sea.
“Thermal models of Pluto’s interior and tectonic evidence found on the surface suggest that an ocean may exist, but it’s not easy to infer its size or anything else about it,” said Johnson in a statement. “We’ve been able to put some constraints on its thickness and get some clues about composition.”
The research, published in Geophysical Review Letters, focuses on Sputnik Planum. The region is a former meteor crater, formed when a object 200 kilometers (125 miles) wide hit Pluto.
A crucial clue about this work comes not from Pluto but from its moon Charon. Charon and Pluto are tidally locked, meaning they always show the same face to each other. Sputnik Planum sits directly under Charon, an indication that there’s a gravitational anomaly in the region.
The researchers think that the impact that formed the heart was followed by a rebound that pulled denser material from deep within the dwarf planet interior. Water is denser than ice, so it might have filled the crater basin, which was later covered in nitrogen ice. This makes the region more massive than the rest of the Plutonian surface, and thus explains the gravitational anomaly.
“This scenario requires a liquid ocean. We wanted to run computer models of the impact to see if this is something that would actually happen,” Johnson added.
The model used a variety of parameters from no water at all to an ocean 200 kilometers (124 miles) deep. They also changed the salinity of the potential ocean. A 100-kilometer thick, 30-percent-salinity ocean was the scenario that best reconstructed what we see in Sputnik Planum.
“It’s pretty amazing to me that you have this body so far out in the Solar System that still may have liquid water,” Johnson concluded.
Researchers hope that more analysis of the New Horizons data will provide more information about the interior workings of Pluto.