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Shear heating as the origin of the plumes and heat flux on Enceladus

Nature volume 447, pages 289–291 (2007)Cite this article

Abstract

Enceladus, a small icy satellite of Saturn, has active plumes jetting from localized fractures (‘tiger stripes’) within an area of high heat flux near the south pole1,2,3,4. The plume characteristics1 and local high heat flux2 have been ascribed either to the presence of liquid water within a few tens of metres of the surface1, or the decomposition of clathrates5. Neither model addresses how delivery of internal heat to the near-surface is sustained. Here we show that the most likely explanation for the heat2 and vapour production6,7 is shear heating by tidally driven lateral (strike-slip) fault motion1,8,9 with displacement of ∼0.5 m over a tidal period. Vapour produced by this heating may escape as plumes through cracks reopened by the tidal stresses10. The ice shell thickness needed to produce the observed heat flux is at least 5 km. The tidal displacements required imply a Love number of h2 > 0.01, suggesting that the ice shell is decoupled from the silicate interior by a subsurface ocean. We predict that the tiger-stripe regions with highest relative temperatures will be the lower-latitude branch of Damascus, Cairo around 60° W longitude and Alexandria around 150° W longitude.

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Figure 1: Shear heating model.
Figure 2: Heat flow and vapour flux as a function of shear velocity u and parameter α.
Figure 3: Predicted tiger-stripe stresses.
Figure 4: Effect of interior structure on mean shear velocity.

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Acknowledgements

We thank D. Gleeson and Z. Crawford for their efforts. This work was funded by NASA’s Planetary Geology and Geophysics and Outer Planets Research programmes.

Author information

Authors and Affiliations

  1. Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA,

    F. Nimmo

  2. Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Boulder, Colorado 80304, USA,

    J. R. Spencer

  3. Planetary Science and Life Detection Section, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 183-301, Pasadena, California 91109, USA,

    R. T. Pappalardo

  4. Department of Astrophysical and Planetary Sciences, Campus Box 391, University of Colorado, Boulder, Colorado 80309-0391, USA,

    M. E. Mullen

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  1. F. Nimmo
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  2. J. R. Spencer
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  4. M. E. Mullen
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Correspondence to F. Nimmo.

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Supplementary information

Supplementary Notes

This file contains Supplementary Notes divided into four sections: 1) scaling tidal strain rates and stresses from Europa to Enceladus; 2) calculating the resolved stresses on a fault; 3) details of the shear heating model, including estimates of the minimum shell thickness required; 4) details of the vapour transport model. It also contains four Supplementary Figures. (PDF 391 kb)

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Nimmo, F., Spencer, J., Pappalardo, R. et al. Shear heating as the origin of the plumes and heat flux on Enceladus. Nature 447, 289–291 (2007). https://doi.org/10.1038/nature05783

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