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S.J. Kortenkamp, G.W. Wetherill (DTM, Carnegie Institution of Washington)
Recent discoveries of extrasolar giant planets orbiting very close to their central stars have revived discussion about the origin and evolution of Jupiter and Saturn. Recent work by A. Boss suggests that Jupiter and Saturn may have formed from gravitational instabilities in the cool outer regions of the early solar nebula. Gravitational interactions between the massive planets and the even more massive gaseous disk then cause the planets to migrate inwards, presumably giving rise to the small orbits of the known extrasolar giant planets.
Formation times scales in Boss' models are ~100 years, implying that the giant planets may have formed long before the formation of the asteroids and terrestrial planet embryos. Using a symplectic N-body integrator modified to account for gas drag we modeled the orbital evolution of planetesimals near 2.6 AU subject to Jupiter and Saturn perturbations. We found the relative velocities (Vr) of planetesimals to be moderately dependant on their size and strongly dependent on the heliocentric distance of Jupiter. With Jupiter at 5.2 AU Vr<800 m/s, with Jupiter at 6.2 AU Vr<500 m/s, and with Jupiter at 7.2 AU Vr<180 m/s.
An accompanying abstract by the authors discusses the consequences of these relative velocities on the growth of asteroids.