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K. Ohtsuki (U. Colorado), H. Tanaka (Tokyo Inst. Tech.)
We study the rate of radial diffusion of planetesimals due to gravitational encounters. We calculate the viscosity in a swarm of equal-sized planetesimals using three-body orbital integrations, and obtain a semi-analytic expression that reproduces these numerical results. We find that the viscosity is independent of the velocity dispersion of planetesimals when the velocity dispersion is so small that Kepler shear dominates planetesimals' relative velocities. On the other hand, in high velocity cases where random velocities dominate the relative velocities, the viscosity is a decreasing function of the velocity dispersion. We also calculate the rate of radial diffusion of planetesimals due to gravitational perturbation by a protoplanet. Using these results, we obtain a condition of gap formation by a protoplanet embedded in a planetesimal disk, which can explain the results of previous N-body simulations.
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Bulletin of the American Astronomical Society, 34, #3
© 2002. The American Astronomical Society.