Direct large-scale N-body simulations of planetesimal dynamics

We describe a new direct numerical method for simulating planetesimal dynam ics in which N similar to 10(6) or more bodies can be evolved simultaneousl y in three spatial dimensions over hundreds of dynamical times. This repres ents several orders of magnitude improvement in resolution over previous st udies. The advance is made possible through modification of a stable and te sted cosmological code optimized for massively parallel computers. However, owing to the excellent scalability and portability of the code, modest clu sters of workstations can treat problems with N similar to 10(5) particles in a practical fashion. The code features algorithms for detection and resolution of collisions and takes into account the strong central force field and flattened Keplerian disk geometry of planetesimal systems. We demonstrate the range of problems that can be addressed by presenting simulations that illustrate oligarchic growth of protoplanets, planet formation in the presence of giant planet p erturbations, the formation of the jovian moons, and orbital migration via planetesimal scattering. We also describe methods under development for inc reasing the timescale of the simulations by several orders of magnitude. (C ) 2000 Academic Press.