DDA 33rd Meeting, Mt. Hood, OR, April 2002
Session 12. Protoplanetary Disks
Tuesday, April 23, 2002, 4:20-6:00pm

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[12.05] Oligarchic Growth Before and After Gas Dispersal

E. W. Thommes (UC Berkeley, CA), M. J. Duncan (Queen's University, Ontario), H. F. Levison (Southwest Research Institute, CO)

Runaway growth ends when the largest protoplanets dominate the dynamics of the planetesimal disk; the subsequent self-limiting accretion mode is referred to as ``oligarchic growth'' (Kokubo and Ida, Icarus 1998, 2000). Here, we expand on our previous investigation of oligarchic growth. We include the effect of gas drag-induced orbital decay of planetesimals, which acts to reduce the final protoplanet masses. Our model predicts find that a fairly massive protoplanetary disk, of order ten times the minimum mass, is required in order to form gas giant planets by core accretion during the lifetime of the nebular gas (about 10 Myrs or less); numerical simulations suggest that the actual accretion efficiency is even lower. The in-situ formation of Uranus- and Neptune-mass ``ice giants'' during this same time appears to be ruled out for any plausible disk mass. We also look at the much slower process of gas-less oligarchic growth, and derive limits on the conditions under which the formation of ice giants in the trans-Saturnian region, in less than the age of the Solar System, could be possible.

This work is supported by NASA's Origins of Solar Systems (EWT and HFL), Planetary Geology and Geophysics (HFL), and Exobiology (HFL) programs, and by NSERC (MJD)

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Bulletin of the American Astronomical Society, 34, #3
© 2002. The American Astronomical Society.