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Powering prolonged hydrothermal activity inside Enceladus

Nature Astronomy volume 1, pages 841–847 (2017)Cite this article

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Abstract

Geophysical data from the Cassini spacecraft imply the presence of a global ocean underneath the ice shell of Enceladus1, only a few kilometres below the surface in the South Polar Terrain2,3,4. Chemical analyses indicate that the ocean is salty5 and is fed by ongoing hydrothermal activity6,7,8. In order to explain these observations, an abnormally high heat power (>20 billion watts) is required, as well as a mechanism to focus endogenic activity at the south pole9,10. Here, we show that more than 10 GW of heat can be generated by tidal friction inside the unconsolidated rocky core. Water transport in the tidally heated permeable core results in hot narrow upwellings with temperatures exceeding 363 K, characterized by powerful (1–5 GW) hotspots at the seafloor, particularly at the south pole. The release of heat in narrow regions favours intense interaction between water and rock, and the transport of hydrothermal products from the core to the plume sources. We are thus able to explain the main global characteristics of Enceladus: global ocean, strong dissipation, reduced ice-shell thickness at the south pole and seafloor activity. We predict that this endogenic activity can be sustained for tens of millions to billions of years.

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Fig. 1: Tidal friction in the porous core of Enceladus saturated with liquid water.
Fig. 2: Synthetic characteristics for porous convection of liquid water with heterogeneous tidal heating of the rocky core.
Fig. 3: Heat flux pattern at the interface between rocky core and ocean.
Fig. 4: Hotpots at the seafloor.

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Acknowledgements

The research leading to these results received financial support from the CNRS PICS (G.C., G.T.), the CNRS-INSU PNP program (G.C., G.T.) and the ANR OASIS project (G.C., G.T.), from the Czech Science Foundation project 15-14263Y (OS), from the German Research Foundation DFG projects PO 1015/2-1, /3-1, /4-1 (F.P.) and from the Icy Worlds node of NASA’s Astrobiology Institute 13-NAI7-0024 (C.S.). The computations were carried out using CCIPL computational facilities (France).

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Authors and Affiliations

  1. Laboratoire de Planétologie et Géodynamique, UMR-CNRS 6112, Université de Nantes, 44322, Nantes Cedex 03, France

    Gaël Choblet & Gabriel Tobie

  2. Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA

    Christophe Sotin

  3. Charles University, Department of Geophysics, V Holešovičkách 2, 180 00, Praha 8, Czech Republic

    Marie Běhounková & Ondřej Čadek

  4. Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 236, 69120, Heidelberg, Germany

    Frank Postberg

  5. Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 236, 69120, Heidelberg, Germany

    Frank Postberg

  6. Charles University, Mathematical Institute, Sokolovská 83, 186 75, Praha 8, Czech Republic

    Ondřej Souček

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  1. Gaël Choblet
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Contributions

All authors contributed to the discussions and commented on the manuscript. G.C. and G.T. led the writing of the letter. C.S. performed calculations on core porosity. G.T. computed the tidal dissipation in the porous core. G.C. developed the 3D code of porous water flow and conducted the numerical simulations of porous convection. All authors contributed to the interpretation of results.

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Correspondence to Gaël Choblet.

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Supplementary Sections 1–2, Supplementary References, Supplementary Tables 1–4, and Supplementary Figures 1–9

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Choblet, G., Tobie, G., Sotin, C. et al. Powering prolonged hydrothermal activity inside Enceladus. Nat Astron 1, 841–847 (2017). https://doi.org/10.1038/s41550-017-0289-8

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