Early Phases of Jupiter's Formation from an Evolving Disk of Solids

Abstract:

We are performing calculations of the formation of Jupiter via core nucleated accretion and gas capture. The calculations model the growth of a solid core from an evolving disk of planetesimals and the growth of a contracting gaseous envelope. We present results of the early phases of formation. The evolution of the solids accounts for growth and fragmentation, viscous and gravitational stirring, and for drag-assisted migration and velocity damping operated by the disk's gas. The envelope structure accounts for mass and energy deposition due to the ablation of planetesimals that move through the envelope. The envelope’s opacity takes into account coagulation and sedimentation of dust particles released by ablating planetesimals. The core starts as a seed body of 350 km in radius, orbiting at 5.2 AU in a disk of planetesimals whose initial radii range from 15 m to 50 km. The initial surface density of the solids is 10 g/cm^2 at the seed’s location. During the evolution of the solids, most of the mass resides in bodies of several tens of km in radius. These are also the planetesimals that provide most of the solids accretion to the planet. By comparing results with a calculation that does not account for the envelope bound to the core, we find that the size-dependent cross-section of the planet for the accretion of planetesimals is substantially enhanced by a low-mass, but voluminous envelope. The calculation without the envelope produces a core of 4.4 Earth masses (Mearth) after about 1 Myr, and an extrapolated mass of about 5 Mearth after 6 Myr. The full calculation with envelope yields a core of 7.3 Mearth and an envelope of 0.15 Mearth after about 0.4 Myr. At this point of the planet's evolution, the envelope accretion rate exceeds that of the core. Over the following 1 Myr, the core mass reaches about 8 Mearth and the envelope mass grows to about 4 Mearth. Support from NASA Outer Planets Research Program is gratefully acknowledged.