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. One project I have completed recently is to explain why the geyser on Enceladus is almost exactly at the south pole. It turns out that if there is warm ice in the subsurface (see Figure below), 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. I am now working with James Roberts, a post-doc, to see whether other moons might have undergone similar reorientations. A long-term collaborator is Bob Pappalardo, now at JPL.
Figure 1. Artist's impression of area of warm ice within Enceladus responsible for geysering and reorientation (see the Nature article for more details).
PhD Opportunities (click here for more
details)
There are a large number of projects that I am interested in pursuing, of which two are particularly suitable for graduate students. One is investigating the extent to which compositional convection, as opposed to thermal convection, may be responsible for surface features such as domes and bands. Compositional convection is a strong contender because it can generate larger stresses, and thus bigger topography, than thermal convection, but very little work has been done on it in the icy satellite context.
The other project is using newly-obtained topography to investigate surface processes on the icy satellites. For instance, by looking at how the topographic power varies with wavelength, we can assess the wavelength range over which processes such as erosion or mass-wasting are important, and thus infer the rate at which the surface is being modified. Nobody has yet tried this for the icy satellites, though similar efforts are underway on Mars.
Publications
Here is a list of recent papers on icy satellites:
· Diapir-induced reorientation of Saturn's moon Enceladus, F. Nimmo and R.T. Pappalardo, Nature , 441, 614-616, 2006. Reprint (PDF)
· Thermal and topographic tests of Europa chaos formation models from Galileo E15 observations, F. Nimmo and B. Giese, Icarus (Europa special issue) , 177, 327-340, 2005. Reprint (PDF)
· A shear heating origin for ridges on Triton , L.M. Prockter, F. Nimmo and R.T. Pappalardo, Geophys. Res. Lett., 32, L14202, 2005. Reprint (PDF)
· Stresses generated in cooling viscoelastic ice shells: Application to Europa, F. Nimmo, J. Geophys. Res. , 109, E12001, 2004 Reprint
· Furrow flexure and ancient heat flux on Ganymede, F. Nimmo and R.T. Pappalardo, Geophys. Res. Lett. , 31, L19701, doi:10.1029/2004GL020763, 2004 Reprint
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Last Modified: 1st Aug 2006.