Accumulation of Giant Planet Atmospheres Around Cores of a Few Earth Masses

Details Accumulation of Giant Planet Atmospheres Around Cores of a Few Earth Masses Accumulation of Giant Planet Atmospheres Around Cores of a Few Earth Masses

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p22c0415h&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P22C-0415

Physics

5749 Origin And Evolution

Scientific paper

New numerical simulations of the formation and evolution of Jupiter with small mass cores are presented. Earlier studies of the core instability model demonstrated that it was possible for Jupiter to form with a solid core of 10 to 30 M⊕ within the lifetime of the protoplanetary disk of 107 years. However, recent interior models of Jupiter suggest a core mass of about 5 M⊕ . Simulations of the growth of Jupiter were computed where the grain opacity and the initial planetesimal surface density, σ init,Z, in the solar nebula were varied. Decreasing the grain opacity emulates the settling and coagulation of grains within the protoplanetary atmosphere. The implications of halting the solid accretion at selected core mass values during the protoplanet's growth, thus simulating the presence of a competing embryo, were also explored. The effects of adjusting these parameters to determine whether or not gas runaway can still occur for small mass cores on a reasonable time scale were examined. Four series of simulations were computed. Each series consists of a run without a cutoff in the core accretion rate plus one or more runs with a cutoff at a particular core mass. The first series of runs is computed with a grain opacity that is 2% of the interstellar value and σ init,Z = 10 g/cm2. Cutoff runs are computed for core masses of 10, 5, and 3 M⊕ . The second series of Jupiter models is computed with the grain opacity at full interstellar value and σ init,Z = 10 g/cm2. Cutoff runs were computed for core masses of 10 and 5 M⊕ . The third series of runs is computed with the grain opacity at 2% of the interstellar value and σ init,Z = 6 g/cm2. One cutoff run is computed with a core mass of 5 M⊕ . The final series consists of one run which is computed with the grain opacity that is temperature dependent (i.e. 2% of the interstellar value for T <= 500 K and full interstellar value for T > 500 K) and σ init,Z = 10 g/cm2. No cutoff run is computed. Our results demonstrate that decreasing the grain opacity results in reducing the evolution time by more than half of that for models computed with full interstellar grain opacity values. In fact, it is the reduction of the grain opacity in the upper portion of the envelope with T < 500 K that governs the lowering of the formation time. Decreasing the surface density of planetesimals lowers the final core mass of the protoplanet but increases the formation timescale. Finally, a core mass cutoff results in a reduction of the time needed for a protoplanet to evolve to the stage of runaway gas accretion provided the cutoff mass is not too small compared with the crossover mass.

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