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P. Thebault (Observatoire de Paris), A. Brahic, C. Perrot (Universite Paris VII)
We have numericaly studied in previous work (Thebault & Brahic BAAS 29.2810) the importance of the coupled effect of massive proto-Jupiter perturbations with mutual collisions in the inner planetesimals disc. A "collisional diffusion" mechanism, starting from the mean-motion resonant regions (in particular the 2:1 at 3.27 a.u.), had been identified. This process tends to increase mutual relative velocities in the region extending above 1.8 a.u.. Its typical time scale is of the order of a few 100 000 years, which means that this increase of the velocities may have taken place before the completion of the accretion process and that it may have considerably slowed down or even stopped this accretion in the perturbed area. A more complete version of our 3-dimensional deterministic model has been developed in order to study the effect of gas drag on this diffusion mechanism, since gaseous friction may have had a significant influence on the earlier kilometer-sized planetesimals. Different gas densities, planetesimals sizes and perturber's masses have been explored. Preliminary results show that for a "standard" gas density of 10g/cm*cm, a significant slowing down of the collisional diffusion together with a decrease of its amplitude is observed. The time scale of the process now exceeds 1 000 000 years and the diffusion wave does not reach regions below 2.3 a.u. This damping of the collisional diffusion is due to the considerable gaseous friction that planetesimals suffer in the resonant regions (which are the sources for the propagation of the perturbations towards the inner solar system). Other runs with lower gas density, or taking in account the decrease of this gas density with time, show a much smaller damping and an almost "nominal" collisional diffusion. Similar results are obtained by considering bigger initial planetesimals.