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Diapir-induced reorientation of Saturn's moon Enceladus

Abstract

Enceladus is a small icy satellite of Saturn. Its south polar region consists of young, tectonically deformed terrain and has an anomalously high heat flux1,2. This heat flux is probably due to localized tidal dissipation within either the ice shell3 or the underlying silicate core4. The surface deformation is plausibly due to upwelling of low-density material (diapirism5) as a result of this tidal heating. Here we show that the current polar location of the hotspot can be explained by reorientation of the satellite's rotation axis because of the presence of a low-density diapir. If the diapir is in the ice shell, then the shell must be relatively thick and maintain significant rigidity (elastic thickness greater than 0.5 km); if the diapir is in the silicate core, then Enceladus cannot possess a global subsurface ocean, because the core must be coupled to the overlying ice for reorientation to occur. The reorientation generates large (10 MPa) tectonic stress patterns6 that are compatible with the observed deformation of the south polar region2. We predict that the distribution of impact craters on the surface will not show the usual leading hemisphere–trailing hemisphere asymmetry. A low-density diapir also yields a potentially observable negative gravity anomaly.

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Figure 1: Schematic diagram of subsurface diapirism on Enceladus.
Figure 2: Variation of parameters affecting reorientation, and the degree of reorientation itself, as a function of d , the lithospheric thickness.

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Acknowledgements

We thank J. Moore, J. Melosh and M. Mullen for comments. This research was supported by NASA PGG and OPR.

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Correspondence to Francis Nimmo.

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Supplementary information

Supplementary Methods

This file gives the derivation of the degree-two gravitational potential G20 and gives further details on the calculation of the resulting gravity anomaly, the k2 Love numbers of the satellite and the derivation of equation (1) for a tidally-distorted body. (DOC 39 kb)

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Nimmo, F., Pappalardo, R. Diapir-induced reorientation of Saturn's moon Enceladus. Nature 441, 614–616 (2006). https://doi.org/10.1038/nature04821

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