An observed correlation between plume activity and tidal stresses on Enceladus

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Abstract

Saturn’s moon Enceladus emits a plume of water vapour and micrometre-sized ice particles from a series of warm fissures located near its south pole1,2,3,4,5,6,7,8,9,10. This geological activity could be powered or controlled by variations in the tidal stresses experienced by Enceladus as it moves around its slightly eccentric orbit. The specific mechanisms by which these varying stresses are converted into heat, however, are still being debated11,12,13,14,15,16. Furthermore, it has proved difficult to find a clear correlation between the predicted tidal forces and measured temporal variations in the plume’s gas content17,18,19 or the particle flux from individual sources20,21. Here we report that the plume’s horizontally integrated brightness is several times greater when Enceladus is near the point in its eccentric orbit where it is furthest from Saturn (apocentre) than it is when near the point of closest approach to the planet (pericentre). More material therefore seems to be escaping from beneath Enceladus’ surface at times when geophysical models predict its fissures should be under tension12,15,16 and therefore may be wider open.

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Figure 1: Sample VIMS observations of Enceladus and its plume.
Figure 2: Sample vertical profiles of the plume’s brightness.
Figure 3: Variations in the plume’s brightness with phase angle.
Figure 4: Variations in the plume’s corrected brightness with Enceladus’ orbital position.

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Acknowledgements

We acknowledge the support of the VIMS team, the Cassini project and NASA. This work was supported in part by NASA grant NNX12AC29G. The work of C.M.G. on this project was made possible by the Research Experience for Undergraduates programme at Cornell University.

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M.M.H., C.M.G. and P.D.N. performed the data analysis. R.N.C., along with P.D.N., C.S., R.H.B., K.H.B. and B.J.B., planned the observations, and provided the data from the VIMS instrument and the appropriate calibration routines. M.R.S. supported the photometric interpretation of these data. All authors discussed these results.

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Correspondence to M. M. Hedman.

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The authors declare no competing financial interests.

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Hedman, M., Gosmeyer, C., Nicholson, P. et al. An observed correlation between plume activity and tidal stresses on Enceladus. Nature 500, 182–184 (2013). https://doi.org/10.1038/nature12371

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