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S. Charnoz, A. Brahic, P. Thébault (Gamma-Gravitation, Université Paris VII, CEA, France)
In order to understand if the dynamical evolution of a disc of planetesimals may be modified by the presence of a giant planet embryo, simple dynamical models have been studied. We present here the evolution of a disc of few thousands particles orbiting in the potential field of a central body and perturbed by a 5 to 30 Earth's masses embryo. Physical collisions between particles have been considered while gravitational encounters have been neglected. Initial conditions correspond to a cold unperturbed disc of particles where relative velocities are of the order of 10 m/s. Particles initially between one and few Hill radii from the perturber's orbit are put on very eccentric orbits and relative velocities become of the order of 1000 m/s, well beyond the escape velocity of planetesimals. Due to successive violent collisions between particles, the perturbation propagates far away from the perturber, like a heat transfer. A 30 Earth's masses perturber orbiting at 5.2 u.a is able to heat the disk in a region extending from 1.7 a.u to 10 a.u in few 100 000 years. In the perturbed region, a radial mixing and transport of material occur and relative velocities are 100 to 1000 m/s. In few million years, the loss of energy due to collisions cools down the disc. As a function of the perturber's mass, two different cooling regimes appear. For a massive embryo, perturbations are strong but the associated time scales are rather short, while smaller perturbations appear for a small mass perturber, but for a much longer time scale. Potential applications concerning the origin of the asteroid belt are presented. The possible role of fragmentation is also discussed.
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