Robert T. Pappalardo

Diapir-induced reorientation of Saturn's moon Enceladus

Enceladus is a small icy satellite of Saturn. Its south polar region consists of young, tectonically deformed terrain and has an anomalously high heat flux. This heat flux is probably due to localized tidal dissipation within either the ice shell or the underlying silicate core. The surface deformation is plausibly due to upwelling of low-density material (diapirism) 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 satellites 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 patterns that are compatible with the observed deformation of the south polar region. 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.

Chapter 36 – Europa

Europa and her sibling satellites were discovered by Galileo in 1610, and more controversially by Simon Marius at essentially the same time, but it took almost four centuries before any detailed views of their surfaces were seen. In the 1960s, ground-based telescopic observations determined that Europas surface composition is dominated by water ice, as are most other solid bodies in the far reaches of the solar system. This chapter discusses various aspects of the satellite, including the internal structure, global tectonics, landforms, surface composition, thermal state, and surface physical processes.