DDP

Abstract

In a relatively quiescent solar nebula, solid particles settle to form a dense layer in the midplane. The density of this layer is set by a balance between settling and diffusion caused by shear-generated turbulence. I present results of a numerical model for the equilibrium structure of a layer of particles of arbitrary size or a mixture of sizes. Radial drift rates and relative velocities are computed. Another model includes coagulation of particles throughout the thickness of the nebula; it is used to determine timescales for growth of aggregates and their settling, and the range of impact strength necessary for the production of macroscopic bodies by collisional sticking. Finally, a model for gravitational coagulation of bodies in Keplerian orbits is used to infer consequences of initial planetesimal sizes for accretion of planetary embryos.