Dead Zones In Circumplanetary Discs as Formation Sites For Regular Satellites

Regular satellites in the solar system are thought to form within circumplanetary discs. We consider a model of a layered circumplanetary disc that consists of a nonturbulent midplane layer and and strongly turbulent disc surface layers. The dead zone provides a favorable site for satellite formation. It is a quiescent environment that permits the growth of solid bodies. Viscous torques within the disc cause it to expand to a substantial fraction of its Hill radius (~0.4 R_H) where tidal torques from the central star remove its angular momentum. For certain parameters, the dead zone develops into a high density substructure well inside the Hill sphere. The radial extent of the dead zone may explain the compactness of the regular satellites orbits for Jupiter and Saturn. The disc temperatures can be low enough to be consistent with the high ice fractions of Ganymede and Callisto.