Resurfacing and Tectonics of Ganymede and Europa

Thursday, February 19, 4:10pm, 1 LeConte

Adam Showman

Ganymede and Europa, two of Jupiter's Galilean satellites, have icy surfaces that display a record of intense resurfacing and tectonics. 65% of Ganymede's surface consists of bright, resurfaced terrain that has defied understanding since its discovery by Voyager in 1979. The best explanation is that bright terrain formed when liquid water or slush flooded a global system of rift valleys, but there has been no mechanism for pumping dense liquid water onto the surface, confining the flows to the rift valleys, or even producing the near-surface liquid water in the first place. To overcome these problems, I describe calculations showing that ancient tidal heating events can plausibly produce near-surface liquid water, and I describe new mechanisms for delivering the liquid to the surface. In particular, I show that topography associated with rift valleys induces subsurface pressure gradients that can drive negatively buoyant liquid water upward into the rift valleys, naturally helping to explain the bright-terrain morphology. Pros and cons of the model will be discussed.

Next I switch gears and discuss portions of Europa's surface that are covered by pits, domes, and disrupted "chaos" regions. A popular hypothesis is that these features result from solid-state convection in Europa's ice shell, but this hypothesis has not yet been fully tested by quantitative physical models. Here I present numerical simulations of convection in Europa's ice shell that shed light on whether convection can produce the observed features. I will discuss the simulations and their implications in detail.