Formation of Planet-Satellite Systems
Regular satellites provide a probe of the compositional and thermal state in the subnebula at the tail end of giant planet formation. Early models propose the formation of satellites in the circumplanetary nebulae of Jupiter and Saturn (Pollack and Reynolds 1974: Pollack et al. 1976). These models envision a condensation sequence analogous to that of the nebula (e.g., Lewis 1972), such that the compositional gradient of the Galilean satellites results from the thermal gradient of the subnebula and sets a temperature of T ~250 K at the "snowline" near the location of Ganymede. Yet, the Saturnian satellites evince no such trend.
This study analyzes the formation of satellites both in gaseous and gas-poor circumplanetary disks. In the gas-poor case, we rely on the collisional capture of heliocentric planetesimals to deliver both the mass and angular momentum needed for satellite formation - but lose the connection to the thermal state, and rely instead on collisional and other processes to account for compositional differences between satellites. In the gaseous case, we seek to connect the thermal structure of the circumplanetary disk to the compositions of the Galilean satellites and the Saturnian satellites. The objective of this program is to employ constraints obtained from satellite bulk properties to investigate whether the regular satellites of Jupiter and Saturn formed in gas-poor or gaseous environments. Interpretation of satellite observations depends on this issue.