HR: 11:50h
AN: P42A-07    [Abstracts]
TI: Core Accretion - Gas Capture Model for Gas Giant Planet Formation
AU: * Hubickyj, O
EM: hubickyj@pollack.arc.nasa.gov
AF: NASA Ames Research Center, Space Science Building M. S. 245-3, Moffett Field, CA 94035 United States
AU: * Hubickyj, O
EM: hubickyj@pollack.arc.nasa.gov
AF: UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 940564 United States
AU: Bodenheimer, P
EM: peter@ucolick.org
AF: UCO/Lick Observatory, University of California at Santa Cruz, Santa Cruz, CA 940564 United States
AU: Lissauer, J J
EM: jlissauer@mail.arc.nasa.gov
AF: NASA Ames Research Center, Space Science Building M. S. 245-3, Moffett Field, CA 94035 United States
AB: The core accretion - gas capture model is generally accepted as the standard formation model for gas giant planets. This model proposes that a solid core grows via the accretion of planetesimals and then captures a massive envelope from the solar nebula gas. Simulations based on this model (Pollack et al. 1996, Bodenheimer et al. 2000) have been successful in explaining many features of giant planets. We have computed simulations (Hubickyj et al. 2005) of the growth of Jupiter using various values for the opacity produced by grains in the protoplanet's atmosphere and for the initial planetesimal surface density in the protoplanetary disk. We also explore the implications of halting the solid accretion at selected core mass values during the protoplanet's growth. Halting planetesimal accretion at low core mass simulates the presence of a competing embryo, and decreasing the atmospheric opacity due to grains emulates the settling and coagulation of grains within the protoplanet's atmosphere. We examine the effects of adjusting these parameters to determine whether or not gas runaway can occur for small mass cores on a reasonable timescale. Our results demonstrate that reducing grain opacities results in formation times less than half of those for models computed with full interstellar grain opacity values. The reduction of opacity due to grains in the upper portion of the envelope with T ≤ 500 K has the largest effect on the lowering of the formation time. If the accretion of planetesimals is not cut off prior to the accretion of gas, then decreasing the surface density of planetesimals lowers the final core mass of the protoplanet, but increases the formation timescale considerably. 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 sufficiently large. The overall results indicate that, with reasonable parameters, it is possible that Jupiter formed at 5 AU via the core accretion process in 1 Myr with a core of 10 M_⊕ or in 5 Myr with a core of 5 M_⊕. This research has been supported by NASA grant NAG 5--9661 and NASA grant NAG 5--13285 from the Origins of Solar Systems Program. Bodenheimer, P., O. Hubickyj, & J. J. Lissauer 2000. Models of the in situ formation of detected extrasolar giant planets. Icarus 143, 2--14. Hubickyj, O., P. Bodenheimer, & J. J. Lissauer 2005. Accretion of the gaseous envelope of Jupiter around 5 -- 10 Earth--mass core. Icarus, in press. Pollack J. B., O. Hubickyj, P. Bodenheimer, J. J. Lissauer, M. Podolak, & Y. Greenzweig 1996. Formation of the giant planets by concurrent accretion of solids and gas. Icarus 124, 62--85.
DE: 6220 Jupiter
SC: Planetary Sciences [P]
MN: Fall Meeting 2005