Planetesimal Accretion onto Growing Proto–Gas Giant Planets

Abstract

The solar and extra solar gas giants appear to have diverse internal structure and metallicities. We examine a potential cause for these dispersions in the context of the conventional sequential accretion formation scenario, which assumes the initial formation of cores from protoplanetary embryos. In principle, gas accretion onto cores with masses below several times that of the Earth is suppressed by the energy released from the bombardment of residual planetesimals. After the cores have attained their isolation masses, additional mass gain through gas accretion enlarges their feeding zones and brings a fresh supply of planetesimals. However, the relatively low-mass cores have limited influence on exciting the eccentricities of the newly embraced planetesimals. Due to their aerodynamical and tidal interaction with the nascent gas disk, planetesimals on eccentric orbits undergo slow orbital decay. We show that these planetesimals generally cannot pass through the mean motion resonances of the cores, and the suppression of planetesimal bombardment rate enables the cores to accrete gas with little interruption. During growth from the cores to protoplanets, the resonance width of protoplanets increases with their masses. When the resonances overlap with each other, the trapped planetesimals become dynamically unstable