Far out, at the edge of our solar system, there's water. A new study indicates that Pluto appears to still have a liquid ocean under its icy crust.
Using data from the New Horizons space probe, researchers from Brown University found that the dwarf planet has been expanding. If the ocean had “frozen into oblivion” long ago, Pluto would have shrunk.
“Thanks to the incredible data returned by New Horizons, we were able to observe tectonic features on Pluto’s surface, update our thermal evolution model with new data and infer that Pluto most likely has a subsurface ocean today,” said Noah Hammond, a graduate student in Brown’s Department of Earth, Environmental and Planetary Sciences, and the study’s lead author.
Spectacular images from New Horizons have changed the impression of Pluto from a “simple snowball in space” to something more “exotic,” with surface ice composed of water, nitrogen and methane.
Furthermore, the planet is spiked with mountains that are hundreds of meters high in contrast to the now famous “heart-shaped plain.” The surface is also far from static, as the probe revealed sinuous faults “hundreds of kilometers long, as deep as 4 kilometers.”
Those tectonic features, researchers say, point to a strong possibility of a subsurface ocean.
“What New Horizons showed was that there are extensional tectonic features, which indicate that Pluto underwent a period of global expansion,” Hammond said. “A subsurface ocean that was slowly freezing over would cause this kind of expansion.”
The researchers added that despite the frigid temperatures so far from the sun, “there may have been enough heat-producing radioactive elements within Pluto’s rocky core to melt part of the planet’s ice shell.”
Then, researchers said, the melted liquid would have likely refrozen and expanded.
“If Pluto had on ocean that was frozen or in the process of freezing, extensional tectonics on the surface would result, and that’s what New Horizons saw,” the researchers wrote in a news release.
A gravitational “tug of war” with Pluto’s moon Charon could have caused the faults, but researchers say that dynamic has “long since wound down.”
To determine the state of a potential ocean today, the researchers used data from New Horizons and came to the conclusion that a frozen ocean would have caused the planet to contract.
“We don’t see the things on the surface we’d expect if there had been a global contraction,” Hammond said. “So we conclude that ice II has not formed, and therefore that the ocean hasn’t completely frozen.”
Ice II is a more compact form of standard ice, so an ocean of it would "occupy a smaller volume and lead to a global contraction on Pluto, rather than an expansion."
The researchers added that it is possible that if the Pluto’s ice shell were less than 260 kilometers thick, an ocean below could have frozen without causing contraction, but their updated model indicates the ice shell is over 300 kilometers thick.
“Those exotic ices are actually good insulators,” Hammond said. “They may be helping Pluto from losing more of its heat to space. That’s amazing to me,” Hammond said. “The possibility that you could have vast liquid water ocean habitats so far from the sun on Pluto — and that the same could also be possible on other Kuiper belt objects as well — is absolutely incredible.”