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P. Thebault (Observatoire de Paris, Section de Meudon), H. Beust (Observatoire de Grenoble, Universite J. Fourier)
The number density of kilometre-sized planetesimals in the Beta-Pictoris Disc is inferred from 2 independent constrains: 1) by extrapolating the estimated dust density with a size distribution power law 2) by considering the number density of bodies necessary to produce the estimated rate of Falling Evaporating Bodies (FEB) probably responsible for observed time-variable redshifted absorption features (Ferlet et al. 1995, Beust and Morbidelli 1996). These two estimated densities satisfyingly fit for a power law close to the classical r-3.5 size distribution and for FEBs being excited at the 4:1 resonance with a 0.001 stellar mass perturbing planet located at 10 a.u. on an eccentric orbit. For this estimated density, we numerically explore the mutual collisions among the inner planetesimals, as perturbed by this 0.001 stellar mass planet. First estimates of the collision rate and mean encounter velocities tend to show that these collisions may produce a significant amount of dust that may at least partially account for the required dust production in the inner Beta Pictoris disc. The effect of collisions on the resonant FEBs is also studied, with preliminary results showing that ~ 10 suffer one violent collisions before reaching eccentricities high enough to allow evaporation close to the star. The orbits of the produced debris is also numerically investigated.