A Self-consistent Model of the Growth of Jupiter's Core

Details A Self-consistent Model of the Growth of Jupiter's Core A Self-consistent Model of the Growth of Jupiter's Core

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p21c1687h&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P21C-1687

Physics

[5749] Planetary Sciences: Fluid Planets / Origin And Evolution, [6220] Planetary Sciences: Solar System Objects / Jupiter

Scientific paper

We report preliminary results of self-consistent calculations of the assembly of Jupiter's solid core by accretional collisions of planetesimals in the early Solar System. These calculations are performed by using a code that models the accreting solids and a planet formation code to model the core's envelope structure. The planetesimal accretion code simulates the growth of a seed body embedded in a swarm of planetesimals with sizes ranging from ~10 m to ~100 km. The code employs multiple zones at semi-major axes in the swarm and computes the collision rate for each zone as the swarm evolves and the seed body grows, becoming the protoplanetary core. Gravitational stirring due to the mutual interactions of the bodies in the swarm is included, although stirring by the core is usually dominant. Collisions among planetesimals, migration and velocity damping due to the drag of nebular gas are also included. The planet formation code simulates the thermodynamical structure and growth of the core's envelope. The code computes the trajectory and evolution of accreted planetesimals as they travel through the envelope and deposit mass and energy. The effective cross-section for planetesimal capture, as a function of the planetesimal size, is calculated and used in the planetesimal accretion code so that gas drag effects in the core's envelope are properly taken into account. The calculation of the opacity at each depth accounts for sedimentation and coagulation of dust and small grains which are released in the envelope by ablating planetesimals. Previous results imply that, if mutual collisions among planetesimals and gas drag are ignored, the isolation mass of the core is set by the restricted 3-body problem. For a surface density of 10 g/cm2 at Jupiter's orbital distance, the isolation mass is about 10 Earth masses and this typically is typically reached within 1 Myr. However, inclusion of collisional damping reduces eccentricities in the swarm, causing mass to pile up in zones adjacent to the core. This shepherding effect generally decreases the core's growth rate when about half the isolation mass is reached. Growth then continues at a slower rate, as planetesimals diffuse into the core's zone by collisions and gas drag. We find that gas drag in the core's envelope affects the cross-section for capture of planetesimals smaller than ~1 km, even when the envelope is very tenuous. Planetesimals with a radius of order 100 m and smaller, are entirely consumed in the envelope, providing a major source of dust and hence opacity. Support from NASA Outer Planets Research Program is gratefully acknowledged.

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