We have constructed an improved statistical method for the calculation of planetary accumulation using the currently standard model of terrestrial planet formation and using the latest results of planetary dynamical theory. The method is applicable for the range of masses in which velocity changes are dominated by gravitational forces, mutual collisions, and gas drag. Calculations are reported both with and without nebular gas. This method has been compared with N-body simulations, and the results of the two calculations are in agreement. As in earlier calculations, the growth of bodies in this mass range and at 1 AU occurs on a ~105 year time scale and is characterized by the evolution of an initially continuous mass distribution into a bimodal distribution, the high mass end of which consists of runaway bodies in the size range of ~1026 g. In this general way, these results are in agreement with those reported earlier (e.g., Wetherill and Stewart 1993, Icarus106, 190-209), but significant differences are also found as a result of the greater precision of the collision rate and the velocity evolution rate of planetesimals used in the present work.
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