A possible underground ocean on Pluto could be protected by an insulating layer

An article published in the journal “Nature Geoscience” reports the results of a study of the conditions that could allow the presence of an ocean below the dwarf planet Pluto’s surface. A team of researchers analyzed using computer simulations the possibility that under the heart-shaped area called Sputnik Planitia there’s a layer of gas hydrate of the class known as clathrates formed by water and natural gas which acts as an insulator allowing the layer below them it remains warm enough to keep water in its liquid state.

The possibility that Pluto may have or at least had in the past an underground ocean of liquid water was studied several years ago but was based on a number of hypotheses that at the time were impossible to verify. The extraordinary dwarf planet July 14, 2015 flyby by NASA’s New Horizons space probe allowed to gather a lot of new information on its characteristics, opening the doors to new research on what could be hidden under its surface.

Over the last few years research on various celestial bodies of the solar system and on exoplanets has revealed that water is very common in the universe, opening even more to the possibility that there are ocean worlds covered with water and in the solar system dwarf planets and moons with underground oceans. Identifying the presence of water is the first step but it is necessary to try to understand if it can still be in a liquid state: the dwarf planets cool relatively quickly after their formation, so other processes are needed that maintain sufficient heat to avoid freezing water.

Now a team of researchers led by Shunichi Kamata of Hokkaido University tried to simulate the evolution of Pluto’s interior to understand how long it would take for a possible underground ocean to freeze and to create the icy shell that covers it in a uniform thickness. The result is that the ocean would have completely frozen hundreds of millions of years ago, but assuming the presence of an insulating layer of gas hydrates, it would hardly get frozen at all.

The presence of a layer of gas hydrates that form in environments with low temperature, high pressure and a certain level of concentration of natural gas that would probably be methane isn’t a far-fetched hypothesis but one of the possible consequences of the conditions existing on Pluto. The presence of methane trapped as a gas hydrate is consistent with the unusual composition of Pluto’s atmosphere, which is instead poor in methane while nitrogen-rich.

The location and topography of Sputnik Planitia offer the possibility that under it there’s still an ocean under the ice crust that in that region is thinner than the rest of the dwarf planet, as shown in the topographic map, the one on the right of the figures created using images of NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

This research is still based on simulations that match to surveys carried out by the New Horizons space probe but also require some extra hypotheses. In the past various hypotheses were made based on the data collected during that flyby, for example in December 2016 a research illustrated the possibility that Pluto’s underground ocean contained considerable amounts of ammonia, which would work as antifreeze.

In essence, the issue is far from closed but offers new insights into the search for other oceans under the surface of dwarf planets. Moons such as Europa and Enceladus are heated thanks to Jupiter and Saturn’s influence but the assessment of the state of water in dwarf planets is more complex. The interest has grown in recent years thanks to the search for water and studies are important because those oceans could be candidates for hosting life forms.

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