Icy Satellites
The moons of the gas giants (Jupiter, Saturn, Uranus, Neptune) are composed mainly of ice, and are geologically fascinating. For instance, Europa has features which look similar to plate tectonic features on Earth, while tiny Enceladus has a giant geyser blasting off into space. The Galileo spacecraft provided a good look at the satellites of Jupiter, while Cassini is currently doing the same for those of Saturn. I have recently completed two projects on Enceladus. One was to explain why the geysers on Enceladus are almost exactly at the south pole. It turns out that if there is warm ice in the subsurface (see left-hand figure), then Enceladus probably rolled over until this region reached the pole. This hypothesis is testable with future observations of the gravity field of the satellite, and also the distribution of impact craters. The other project was to suggest that the geysers are generated by frictional heating due to faults rubbing back-and-forth against each other (see right-hand figure).
(Left) Artist's impression of an area of warm ice within Enceladus responsible for geysering and reorientation (see the Nature article for more details).
(Right) Artist’s impression of shear-heating on faults generating the observed vapour plumes above the surface (see another Nature article for details).
I am following up some of this work with two post-docs. James Roberts is investigating what these results tell us about the interior and long-term history of Enceladus, in particular whether it has an ocean, while Ke (Chris) Zhang is looking into the orbital evolution of Enceladus. One of my graduate students, Erinna Chen, has just finished a project on the history of Tethys. A long-term collaborator is Bob Pappalardo, now at JPL.
Publications
Here is a list of recent papers on icy satellites:
· The thermal and orbital evolution of Tethys as constrained by surface observations E.M.A. Chen, F. Nimmo Geophys. Res. Lett., 35 , L19203, 2008. Reprint (PDF)
· True polar wander on Europa from global-scale small-circle depressions, P. Schenk, I. Matsuyama and F. Nimmo, Nature 453 368-371, 2008, Reprint Supplementary Info.(PDF)
· Forced obliquity and moments of inertia of Titan B.G. Bills and F. Nimmo, Icarus 196 , 293-297, 2008 Reprint(PDF)
· Near-surface heating on Enceladus and the south polar thermal anomaly J.H. Roberts and F. Nimmo, GRL 35 L09201, 2008, Reprint(PDF)
· Tidal heating and the long-term stability of a subsurface ocean on Enceladus J.H. Roberts and F. Nimmo, Icarus 194 675-689, 2008, Reprint(PDF)
· Shear heating as the origin of the plumes and heat flux on Enceladus, F. Nimmo, J.R. Spencer, R.T. Pappalardo and M.E. Mullen, Nature , 447, 289-291, 2007. Reprint (PDF) Supplementary Info (.pdf)
· Reorientation of icy satellites by impact basins F. Nimmo and I. Matsuyama Geophys. Res. Lett. , 34, L19203, 2007. Preprint (PDF)
· The global shape of Europa: Constraints on lateral shell thickness variations, F. Nimmo, P.C. Thomas, R.T. Pappalardo, W.B. Moore, Icarus , 191, 183-192, 2007. Preprint (PDF)
· Rotational stability of tidally deformed planetary bodies I. Matsuyama and F. Nimmo J. Geophys. Res. , 112, E11003, 2007. Reprint (PDF)
· Diapir-induced reorientation of Saturn's moon Enceladus, F. Nimmo and R.T. Pappalardo, Nature , 441, 614-616, 2006. Reprint (PDF) Supplementary Info (.doc)
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Last Modified: 16th Oct 2009.