Turbulence effects in planetesimal formation

The formation of planetesimals is investigated by studying the transport of dust particles in a local three-dimensional simulation of accretion disc turbulence. Heavy particles fall rapidly towards the midplane, whereas lighter particles are strongly advected by the flow. For light particles the turbulence leads to a rapid redistribution of particles such that their density per unit mass is approximately constant with height. There is no pronounced concentration of particles in vortices or anticyclones, as was suggested previously. This is partly because of the adverse effect of keplerian shear and also because in our simulation vortices are only short lived. However, if we assume the gas velocity to be frozen in time, there is a concentration of dust in ring-like structures after a few orbits. This is caused mainly by a convergence of the gas flow in those locations, rather than the presence of vortices or anticyclones.