1. Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA
2. Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Boulder, Colorado 80304, USA
3. Planetary Science and Life Detection Section, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 183-301, Pasadena, California 91109, USA
4. Department of Astrophysical and Planetary Sciences, Campus Box 391, University of Colorado, Boulder, Colorado 80309-0391, USA

Correspondence to: F. Nimmo¹ Correspondence and requests for materials should be addressed to F.N. (Email: fnimmo@es.ucsc.edu).

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 pole^{1, 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 production^{6, 7} is shear heating by tidally driven lateral (strike-slip) fault motion^{1, 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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