Strain rates and heat fluxes on icy satellites

Thursday, February 12, 4:10pm, 1 LeConte

W.H. Francis Nimmo

The satellites of Jupiter are a good example of the diversity observed in this solar system, the causes of which remain obscure. Explaining this diversity requires characterization of both the satellites' present-day state, and their thermal and orbital evolution. Two particularly important parameters to characterize are heat flux and strain rate.

Flexural profiles across terrains of different ages on Ganymede can be used to obtain estimates of how the surface heat flux has varied with time. The estimated heat fluxes are considerably in excess of likely chondritic values, and estimates of recent heat fluxes on Europa. However, the heat fluxes are compatible with estimates of the transient tidal dissipation produced during Ganymede's capture into the Laplace resonance. The estimated heat fluxes also have implications for the state of Ganymede's ice shell (convecting vs. conducting), and the fact that it has a present-day dynamo.

An example of planetary diversity is that extension is accommodated in very different fashions on Europa and Ganymede. Rifts on Europa are narrow and have high stretching factors; rifts on Ganymede are broad with lower stretching factors. A simple model of extension on icy satellites demonstrates that Europa-type rifts are favoured at high strain rates or low heat fluxes, while the converse is true for Ganymede-style rifts. The Ganymede heat fluxes inferred are compatible with the results obtained above; the strain rates for Europa constrain the likely processes responsible for rifting.