Formation of the giant planets and their satellite-ring systems: An overview

This paper presents an overview of the nature of the outer giant planets and their satellite and ring systems, theories of their origins, and models of the planets' evolution. The giant planets may have formed either as a result of gravitational instabilities in the solar nebula that gave rise to their envelopes, with their cores being formed later (the gas-instability hypothesis); or as a result of the formation of massive solid cores, chiefly by binary accretion of smaller planetesimals, which permanently captured massive amounts of gas from the surrounding solar nebula (the core-instability hypothesis). Neither model fits all the relevant observational constraints in an obvious fashion. However, the core-instability hypothesis is currently favored because it leads to a ''first principles'' prediction of the value and near constancy of the core masses