Accretional evolution of a planetesimal swarm: 1. A new simulation

Abstract

We describe a new simulation for planetary accretion which treats simultaneous accretion in many interacting heliocentric distance zones, rather than the single one characteristic of earlier models. The planetesimals are characterized by keplerian elements rather than a single “random velocity.” This numerical code can follow the evolution of both the size distribution and the orbit element distribution of a planetisimal swarm from any initial distributions of sizes and orbits. It also can treat a small number of the largest bodies as discrete objects with individual orbits, rather than as part of the continuum size distribution. We describe the structure of this model, results of testing the code against two analytic solutions of the coagulation equation, and comparison of our results with those of other workers. We find that our accretion algorithm yields good agreement with the analytic solutions. We also find agreement with the results of Wetherill and Stewart (1989, Icarus 77, 330–357) for gravitational accretion of planetesimals with equivalent initial conditions. In addition, we demonstrate accretion in multiple heliocentric zones.