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F. Marzari (Universita di Padova), S. J. Weidenschilling (Planetary Science Institute)
Under the assumption that gas persisted in the asteroid region for some time after Jupiter attained its final mass, the combined effects of Jupiter's resonant perturbations and nebular gas drag inject a significant fraction of planetesimals populating the asteroid region into highly eccentric orbits with supersonic velocities relative to the gas. We have identified two distinct dynamical mechanisms that can excite high eccentricities despite the damping effects of gas drag: 2:1 resonance trapping and diffusion from the 3:2 resonance. If Jupiter's eccentricity was comparable to the present one, planetesimals entering the 2:1 resonance can be temporarily trapped and have their eccentricities pumped up by the resonant perturbations. A significant fraction of bodies entering the 3:2 resonance leave the resonance without encountering Jupiter and they diffuse in a region of phase space with high-order overlapping resonances. Both mechanisms can generate eccentricities of the order of 0.5 or higher for large size planetesimals (50-500 km in diameter). The large eccentricities cause enhanced orbital decay and rapid migration of bodies from the outer to the inner asteroid belt. During their migration, these planetesimals have a significant collisional evolution, since the resonant perturbations do not affect their inclinations, which remain low. The supersonic velocities attained by the resonant planetesimals would be a source of shock waves in the solar nebula with implications for chondrule formation.