Oligarchic growth of giant planets

Authors:
Edward W. Thommes,
Martin J. Duncan,
Harold F. Levison

Comments: ScienceDirect already has the final published version here:
dx.doi.org/10.1016/S0019-1035(02)00043-X

Journal-ref: Icarus 161, 2003, 431-455

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.” Here, we begin by expanding on the existing
analytic model of the oligarchic growth regime. From this, we derive global
estimates of the planet formation rate throughout a protoplanetary disk. We
find that a relatively high-mass protoplanetary disk ($sim$ 10$ imes$
minimum-mass) is required to produce giant planet core-sized bodies ($sim$ 10
M$_{oplus}$) within the lifetime of the nebular gas ($la$ 10 million years).
However, an implausibly massive disk is needed to produce even an Earth mass at
the orbit of Uranus by 10 Myrs. Subsequent accretion without the dissipational
effect of gas is even slower and less efficient. In the limit of
non-interacting planetesimals, a reasonable-mass disk is unable to produce
bodies the size of the Solar System’s two outer giant planets at their current
locations on {it any} timescale; if collisional damping of planetesimal random
velocities is sufficiently effective, though, it may be possible for a
Uranus/Neptune to form in situ in less than the age of the Solar System. We
perform numerical simulations of oligarchic growth with gas, and find that
protoplanet growth rates agree reasonably well with the analytic model as long
as protoplanet masses are well below their estimated final masses. However,
accretion stalls earlier than predicted, so that the largest final protoplanet
masses are smaller than those given by the model. Thus the oligarchic growth
model, in the form developed here, appears to provide an upper limit for the
efficiency of giant planet formation.

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