Proto-Jupiter Perturbations on a System of Colliding Planetesimals

P. Thebault, A. Brahic (Universite Paris VII France)

We have developed a numerical model in order to quantitatively study the influence of a Proto-Jupiter on the accretion process of planetesimals. The proto-planetary disk is modeled by an optically thin tri-dimensional system of colliding particles. The perturbations of their keplerian orbits by the Proto-Jupiter are computed using Gauss' perturbing equations (Thebault & Brahic BAAS 28). We study, as a function of time, the distribution of relative velocities, which depends on the eccentricity and inclinaison distribution and on the phasing of the perturbed orbits.

New results, based on several runs with different disk characteristics (optical depth, collision rate...), are presented here. They all show that, within time scales of a few 10000 years, mutual collisions propagate the initially resonant pertubations (mostly the 2:1 and 3:1) towards the inner parts of the disk, until a location close to the actual martian orbit. In this perturbed region, mean relative velocities are much higher than the escape velocities of kilometer-sized bodies. Accretion is then completely stopped if the time scale of this diffusion mechanism is shorter than the runaway accretion time leading to large planetary embryos. If not, the biggest embryos continue to accrete material at an increased rate. It happens that both time scales have the same order of magnitude. A careful study of both mechanisms coupled in the same model has then to be performed in order to understand planetary accretion.

If we put the perturber on an eccentric orbit, then higher order resonances (3:1, 4:1) are enhanced. Outside mean motion resonances, we also observe a important rise of the particles eccentricities, but this additional phenomenon corresponds to phased orbits and does not lead to a significant increase of relative velocities. Only collisional diffusion from mean motion resonances seems to be an efficient mechanism to change the dynamical conditions of mutual encounters on a large scale..