Direct Simulation of Planet Formation With a Million Planetesimals

D. C. Richardson, T. Quinn, G. Lake (University of Washington)

We describe techniques for direct simulation of planet formation using tex2html_wrap_inline20 or more planetesimals over timescales of tex2html_wrap_inline22 yr or longer. This represents several orders of magnitude improvement over any previous direct studies (e.g. Beaugé & Aarseth 1990, MNRAS 245, 30; Aarseth et al. 1993, ApJ 403, 351; Kokubo & Ida 1997, Icarus 123, 180). This improvement will be made possible by modification of a spatially adaptive cosmology code designed to run on massively parallel supercomputers (Stadel & Quinn, in preparation). With such unprecedented spatial and temporal resolution, we will address fundamental questions regarding the origin of solar systems: the primordial mass distribution, the likely extent of radial mixing, the cause of mass depletion in the asteroid belt, the origin of planetary spins and obliquities, the likelihood that the Moon was formed by a late massive impact, and the role of giant planets in terrestrial planet formation. This last point is critical to help direct future ExNPS searches for terrestrial planets, since current survey techniques are limited to finding stars with giants (e.g. Marcy & Butler, BAAS 28, 1314). Our code is being modified to detect and process collisions between planetesimals and will support agglomeration, bouncing, cratering (mass transfer), and fragmentation, with provision for gas drag. Initially we will focus on the formation of rocky terrestrial planets. We will quantitatively show for the first time the transition from runaway growth to the final accumulation of protoplanets into planets. In the long term we will incorporate cosmology hydrocode to investigate giant planet formation in the volatile-rich outer nebula. We present here a description of our method, a plan of work to be carried out in the next year, and preliminary results from a feasibility study.