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R.A. Murray-Clay, E.I. Chiang (UC Berkeley)
A residual planetesimal disk of mass \sim10--100 M_\oplus likely remained in the outer solar system following the formation of the giant planets, as suggested by the existence of the Oort cloud, formation requirements for Pluto, and inefficiencies in planet formation. Upon gravitationally scattering planetesimal debris, planets migrate. Orbital migration may explain resonant populations in the Kuiper belt and the asteroid belt. Finite sizes of planetesimals render migration stochastic (``noisy''). At fixed disk mass, larger (fewer) planetesimals generate more noise. Extreme stochasticity defeats resonance capture. We employ order-of-magnitude physics and numerical experiments to construct a general theory for how a planet's semi-major axis fluctuates in response to discrete scattering events. The degree of stochasticity depends not only on the number densities of planetesimals, but also on how their orbital semi-major axes and eccentricities are distributed. To maintain the viability of resonance capture, planetesimals must be sufficiently small; we apply our theory to estimate the maximum planetesimal size compatible with resonance capture by a migrating Neptune. This maximum size of 600 km applies to those planetesimals comprising the bulk of the mass of the disk.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.