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H. Hussmann, T. Spohn (Institut für Planetologie, Münster, Germany)
The orbital dynamics of the three inner Galilean satellites Io, Europa and Ganymede are driven by resonant locks, which maintain the satellites' orbital eccentricities over long periods of time. The resulting tidal forces tend to circularize their orbits and to drive them out of resonance. This is counterbalanced by torques exerted on the satellites by Jupiter. As another consequence of the resonance locking, orbital energy gained by the satellites (especially by Io as the closest to Jupiter) is shared among all three satellites. Dissipation of orbital energy due to tidal friction is an important internal heat source and provides a coupling between the thermal and orbital evolutions of the satellites. The dissipation rate in an individual satellite, here parameterized by the imaginary part of the tidal Love number k2 using a Maxwell rheology model, depends on the orbital parameters, on the structure of the satellite, and on the viscosities and shear moduli of its viscoelastic layers. The viscosities and the shear moduli are taken to be temperature dependent. The occurrence of partial melt in Io's silicate layer and the existence of a sub-surface ocean on Europa, which decouples the dissipative ice layer from the interior, will have a strong influence on the dissipation rates and thus on the orbital evolution.\\ We discuss the distribution of orbital and thermal energy between the satellites during their evolution in the Laplace resonance while focusing on Europa. Possible oscillations of the orbital elements of Europa will be shown to cause oscillations in tidal dissipation rate and ice shell thickness. Variations of the latter will have a feedback effect on the dissipation rate and thus on the orbital evolution of the satellites. We speculate that particular surface features on Europa may be interpreted as remnants of differing phases of tidal dissipation. For instance, Lenticulae could have formed at times when the ice shell was thick enough (several tens of kilometers) to allow convection and uprising plumes while chaos terrain may have formed when the ice was thin.
The author(s) of this abstract have provided an email address for comments about the abstract: hhussman@uni-muenster.de