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P. Tanga, P. Michel (OCA), D.C. Richardson (Maryland Univ.)
The usual approach to the study of planetary accretion always considers homogeneous distributions of planetesimals and isotropic velocity dispersions. Nevertheless, if small planetesimals (in the 1 cm - 1 m range) were affected by the turbulent gas disk motion, several studies have suggested that the properties of homogeneity could be easily lost (see e.g. Tanga et al. 1996, Bracco et al. 1999, Godon and Livio 2000). In fact, due to gas drag, surface density fluctuations can appear, as well as a correlation in planetesimal velocities. In particular, the presence of vortices seems to be very effective in this sense. Unfortunately, if a dust surface density close to that of a "Minimum Mass" Solar Nebula is assumed, the numerical integration of self-gravitating planetesimal systems in the concerned size range is not possible due to the huge number of particles involved. Therefore, our first step has been the investigation of the role of pure self-gravitation in the evolution of planetesimal clusters in disks of 104 - 106 bodies (implying thus much larger bodies) by use of the gravitational N-body code pkdgrav. Preliminary results clearly show that under certain conditions a local planetesimal clustering can remain compact over several disk revolutions, provided that a velocity correlation among neighbouring particles is present. An appropriate rescaling of these results toward planetesimals of smaller sizes shows that cluster survival is relevant in affecting their dynamics, collisional properties and growth rate. These processes could then be very relevant in the early stages of planetary system formation.
The author(s) of this abstract have provided an email address for comments about the abstract: tanga@obs-nice.fr