37th DPS Meeting, 4-9 September 2005
Session 29 Planet and Satellite Formation
Poster, Tuesday, September 6, 2005, 6:00-7:15pm, Music Foyer

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[29.12] The Effects of Atmospheric Opacity on Giant Planet Growth Rates

J. J. Lissauer (NASA Ames), O. Hubickyj (NASA Ames, UCSC), P. Bodenheimer (UCSC)

Observations of protoplanetary disks imply that gas giant planets form in less than 10 Myr. Recent interior models of Jupiter suggest smaller core masses (0 - 10 Earth mass) than had been previously estimated (10 - 30 Earth mass). We have computed several evolutionary simulations of Jupiter based on the core accretion model of gas giant planet formation. The core accretion model states that a solid core is formed from the accretion of planetesimals in the protoplanetary disk followed by the capture of a massive envelope from the solar nebula gas. The primary parameters that we varied from simulation to simulation are the grain opacity in the planet's atmosphere and the planetesimal surface density of the protoplanetary disk. Our results demonstrate that decreasing the atmospheric opacity due to grains to realistic values reduces the formation time by more than half compared with that for models computed with full interstellar grain opacity values. In fact, it is primarily the opacity due to grains in the upper portion of the envelope with T < 500 K that governs the lowering of the formation time. Decreasing the surface density of the planetesimals lowers the final core mass of the protoplanet but increases the formation timescale. Finally, a core mass cutoff results in the 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. Our models show that with reasonable parameters it is possible that Jupiter formed by means of the core accretion process in 3 Myr or less. This research was supported by grants from NASA's Outer Planets Research Program (JJL) and Origins of Solar Systems Program (OH and PB).

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.