Pluto’s heart-shaped region hides an icy sea underneath

The prominent heart-shaped region of Pluto known as Sputnik Planitia may be hiding a slushy liquid water ocean beneath its icy crust, according to two new studies published this week in the journal Nature and based data on collected last summer by NASA’s New Horizons probe.

According to Reuters, the authors of the studies report that the ocean lies between 150 and 200 kilometers (93 to 124 miles) beneath the surface of the dwarf planet, and is roughly 100 km (62 miles) deep, and that this may help explain Pluto’s unusual alignment with its moon Charon.

“If you were to draw a line from the centre of Pluto’s moon Charon through Pluto, it would come out on the other side, almost right through Sputnik Planitia,” James Keane, a doctoral candidate at the University of Arizona and co-author of one of the newly-published papers, told BBC News on Wednesday. “That line is what we call the tidal axis.”

Computer models have suggested that the heart-shaped impact basin was located in its present position because it was filled with ice, causing the dwarf planet to roll over by up to 60 degrees relative to its spin axis while cracking its crust in the process, according to reports. This would have only been possible if Pluto contained a subsurface ocean, the researchers explained.

“If you have a perfectly spherical planet… and you stick a lump of extra mass on the side and let it spin, the planet will re-orient to move that extra mass closer to the equator. For bodies like Pluto that are tidally locked,” Keane told BBC News, “it will move it toward that tidal axis – the one connecting Pluto and Charon.”

Residual heat keeps water liquid… but could Pluto be habitable?

University of California, Santa Cruz professor Francis Nimmo, one of the authors of the other Nature study, told BBC’s Inside Science radio program that Sputnik Planitia contained a greater amount of mass than the surrounding regions. “Somehow,” he said, “there’s extra stuff there.”

That in itself is a bit of a puzzle since the heart-shaped region is believed to have been created following an impact with some unknown object, meaning that it should weigh less, not more, the professor continued. However, if some of the ice believed to be beneath Sputnik Planitia was not ice after all, but water (which is denser), “you’d be adding extra mass,” Nimmo noted.

So how is it that a world located approximately 40 times further from the sun than Earth can be home to an underground ocean of mostly liquid water? As Nimmo told Reuters, it is because the dwarf planet still has enough radioactive heat remaining from its formation more than 4.5 billion years ago to keep water liquid, largely due to heat-generating rock and insulating ice shell.

Naturally, the discovery of liquid water on another planet will raise questions about whether or not it could be capable of supporting microbial life. Given that Pluto’s subsurface ocean is under a thick shell of ice, however, Massachusetts Institute of Technology planetary scientist Richard Binzel, another of the scientists involved in the research, told Reuters that this is unlikely.

“One is careful to never say the word impossible,” though, he added.


Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute