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Pluto’s ocean is capped and insulated by gas hydrates

Nature Geoscience volume 12, pages 407–410 (2019)Cite this article

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Abstract

Many icy Solar System bodies possess subsurface oceans. On 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 its thickness, Pluto’s ice shell needs to be cold. Here we show, by thermal evolution and viscous relaxation calculations, 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 completely freezing while keeping the ice shell cold and immobile. The most likely clathrate guest gas is methane, derived from precursor bodies and/or cracking of organic materials in the hot rocky core. Nitrogen molecules initially contained and/or produced later in the core would probably not be trapped as clathrate hydrates, instead supplying the nitrogen-rich surface and atmosphere. The formation of a thin clathrate hydrate layer cap to a subsurface ocean may be an important generic mechanism to maintain long-lived subsurface oceans in relatively large but minimally heated icy satellites and Kuiper belt objects.

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Fig. 1: A schematic diagram of the interior structure of Pluto.
Fig. 2: Time evolution of the interior thermal profile above the rocky core.
Fig. 3: Timescale of viscous relaxation of the ice shell.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.

Code availability

Codes for the thermal evolution and viscous relaxation calculations are available upon reasonable request from S.K.

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Acknowledgements

This study was supported by KAKENHI from the Japan Society for Promotion of Science (grant nos. JP16K17787, JP17H06456 and JP17H06457) and by the Astrobiology Center Program of the National Institutes of Natural Sciences.

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Author notes

  1. Shunichi Kamata

    Present address: Department of Earth and Planetary, Sciences, Hokkaido University, Sapporo, Japan

Authors and Affiliations

  1. Creative Research Institution, Hokkaido University, Sapporo, Japan

    Shunichi Kamata

  2. Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, CA, USA

    Francis Nimmo

  3. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan

    Yasuhito Sekine

  4. Department of Cosmosciences, Hokkaido University, Sapporo, Japan

    Kiyoshi Kuramoto

  5. Graduate School of Technology, Industrial and Social Sciences, Tokushima University, Tokushima, Japan

    Naoki Noguchi

  6. Department of Earth and Space Science, Osaka University, Toyonaka, Japan

    Jun Kimura

  7. Department of Human Environmental Science, Kobe University, Kobe, Japan

    Atsushi Tani

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Contributions

S.K. developed the idea of this study, conducted thermal evolution and viscous relaxation calculations, created all figures and was the primary author of the manuscript. F.N. participated in numerous discussions and co-wrote the manuscript. Y.S. and K.K. provided information on gas production mechanisms and likely guest gas species of clathrate hydrates. N.N. provided detailed information on clathrate hydrates and calculated their densities. J.K. participated in numerous discussions on thermal evolution models. A.T. provided detailed information on clathrate hydrates formation. All of the authors participated in interpretation of the results.

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Correspondence to Shunichi Kamata.

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Supplementary Figs. 1–9, Table 1 and discussion.

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Kamata, S., Nimmo, F., Sekine, Y. et al. Pluto’s ocean is capped and insulated by gas hydrates. Nat. Geosci. 12, 407–410 (2019). https://doi.org/10.1038/s41561-019-0369-8

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