Internal structure and dynamics of the large icy satellites

The magnetic data returned by the Galileo mission suggest that deep oceans are present within the icy Galilean satellites. In addition, tectonic features on Europa are consistent with models of subsolidus convection within the outer ice I layer. Ice viscosity is a key parameter for modeling the thermal and orbital evolution of these large satellites. Using laboratory experiments and glacier measurements, this article shows that tidal heating is a strong source of internal heating which may explain the presence of a deep ocean within Europa. Another key parameter is the composition of ice. The presence of ammonia, which is likely in Saturn's sub-nebula, decreases so much the melting point temperature of ice that it would inhibit the complete freezing of the ocean. Predictions for the internal structure of Titan are made and will be checked by the Cassini mission which started orbiting Saturn on 1st July 2004.