Radial Concentration of Particles within an Evolving Protoplanetary Disk

Recent theories of planetesimal formation contend that formation via gravitational and or fluid instabilities may occur in regions of enhanced solids content. While settling of solids toward a protoplanetary disk midplane is probably an important component of such concentration, because of disk turbulence it is insufficient to drive collapse into larger bodies. The next logical concentration mechanism is then global concentration of solids via radial drift of particles, and this has been explored to a degree with promising results. Here we combine radial drift of particles with radial diffusion, which acts to counteract the effects of inward particle flux. We use a stocastic model to track the radial mass distribution of a particle ensemble within an evolving protoplanetary disk using a range of particle sizes, and explore the feasibility of globally concentrating solids to a degree that could lead to enhanced planetesimal formation.