Recent findings suggest that Pluto has buried an ocean of liquid water under its icy shell. But how could such a thing be possible on the cold outer edges of the solar system? Scientists from Japan and the US could have an answer.
In an article published on Monday in Nature Geoscience, these researchers speculate that Pluto's ocean may be isolated by a layer of gas under the ice. If this hypothesis proves true, this mechanism could prevent other ice worlds from completely freezing.
"If this mechanism is widespread, then oceans could be spread on other large oceans," said study co-author Francis Nimmo of the University of California, Santa Cruz, to combine Gizmodo with other pieces of evidence. The New Horizons mission flew with Pluto in 2015 and found that geologically it is quite complex. In 2016, the scientists' models suggested that the Sputnik Planitia, the left lobe of the "heart" of the dwarf planet, could have an underground, partially liquid ocean, as found on the icy moons of Jupiter or Saturn.
It's pretty wild to think about it: something so distant and as small as Pluto is not completely frozen, but could have liquid water under its surface. Scientists wondered how this could be possible. Pluto does not have the gravitational energy of a nearby giant planet to maintain the tides and warm the water. Also, the warming caused by the radioactive decay of its elements would not, according to the new publication, help prevent complete freezing. And it seems that there is not enough ammonia on Pluto to dissolve in the water and raise its melting point.
Instead, scientists suggest that the ice shell contains a layer of water cages that trap gas like methane. Without the layer, the ice would dissipate heat from Pluto's interior. However, the gas cage layer of "clathrate hydrate" would have other thermal properties that would slow down the ice's ability to extract heat from the water. And methane inclusion would also explain why scientists in Pluto's atmosphere did not observe much methane, Nimmo said.
The article is "pretty interesting," J. Hunter Waite, Program Director at the Southwest Research Institute, did not participate in this study, Gizmodo said in an email. "Understanding the role of processes such as clathrates enhances the knowledge base for exploring the ocean worlds and their role in the formation and evolution of the solar system, thereby broadening our horizons on what habitable environments are," he continued.
But he warned that scientists still need to know little about Pluto's overall makeup and look for other objects, such as comets and meteorites, to guide their hypothesis.
However, it is still interesting. "Our findings suggest that a long-lived ocean can exist without tidal warming, which is important to preserve the oceans in icy satellites," said first-time author Shunichi Kamata of Hokkaido University in Japan opposite Gizmodo.
New Horizons has flown far beyond Pluto, and there is currently no mission that could prove the existence of these clathrate hydrates. But Nimmo and Kamata hope that in the future a mission can check its results. And maybe there are other icy oceans in the solar system that are kept warm in the same way.