Pluto’s ocean is capped and insulated by gas hydrates

Many icy solar system bodies possess subsurface oceans. At Pluto, Sputnik Planitia’s location near the equator suggests the presence of a subsurface ocean and a locally thinned ice shell. To maintain an ocean, Pluto needs to retain heat inside. On the other hand, to maintain large variations in ice shell thickness, Pluto’s ice shell needs to be cold. Achieving such an interior structure is problematic. Here we show that the presence of a thin layer of clathrate hydrates (gas hydrates) at the base of the ice shell can explain both the long-term survival of the ocean and the maintenance of shell thickness contrasts. Clathrate hydrates act as a thermal insulator, preventing the ocean from complete freezing while keeping the ice shell cold and immobile. The most likely clathrate guest gas is methane either contained in precursor bodies and/or produced by cracking of organic materials in the hot rocky core. Nitrogen molecules initially contained and/or produced later in the core would likely not be trapped as clathrate hydrates, instead supplying the nitrogen-rich surface and atmosphere. The formation of a thin clathrate hydrate layer capping a subsurface ocean may be an important generic mechanism maintaining long-lived subsurface oceans in relatively large but minimally-heated icy satellites and Kuiper Belt Objects.

This is the Author's Accepted Manuscript of the following article: Pluto’s ocean is capped and insulated by gas hydrates, Shunichi Kamata, Francis Nimmo, Yasuhito Sekine, Kiyoshi Kuramoto, Naoki Noguchi, Jun Kimura & Atsushi Tani, Nature Geoscience 12(6), 407-410 (2019), which has been published in final form at https://doi.org/10.1038/s41561-019-0369-8.