Pluto’s Subsurface Ocean

Since the New Horizons probe visited Pluto in 2015, scientists have suspected that Sputnik Planitia (a.k.a. Pluto’s Heart), shown above, may hide a subsurface ocean. But it’s tough to explain how that ocean could stay warm enough to be liquid while the surface ice remains cold and viscous enough to support the variations in thickness we see. One theory cites the possibility of ammonia in the ocean, essentially serving as anti-freeze, but that would require much higher concentrations of ammonia than have been observed in comets – which, like Pluto, spend most of their time in the icy, frigid regions of the Kuiper Belt.

A new study suggests another theory: a layer of gas-trapping hydrates between the liquid ocean and its icy cap. A thin layer of clathrate hydrates, as proposed by the authors, would trap gases like methane and create a thermally-insulating layer between a warm ocean and much colder ice cap. Because heat would struggle to cross the insulation layer, the water beneath would stay above the freezing point without the cold ice above leeching all of its warmth away.

It would likely require future missions to Pluto or other potential ocean worlds to confirm the presence of such a hydrate layer, but, for now, the theory provides a possible new explanation for how icy objects like Pluto maintain liquids. (Image credit: NASA/JHU Applied Physics Laboratory/SwRI; research credit: S. Kamata et al.; via Gizmodo)

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