Planetesimal evolution and the formation of terrestrial planets

To create an accurate numerical model of solar system formation it is necessary to understand how planetesimals, the planetary building blocks, evolve and grow into larger bodies. In order to determine the effects of various collision parameters, I have completed several parameter-space studies of collisions between kilometer-sized planetesimals. The planetesimals are modeled as "rubble piles"---gravitational aggregates of indestructible particles bound together purely by gravity.; I find that as the ratio of projectile to target mass departs from unity the impact angle has less effect on the collision outcome. At the same time, the probability of planetesimal growth increases. Conversely, for a fixed impact energy, collisions between impactors with mass ratio near unity are more dispersive than those with mass ratio far from unity. Net accretion dominates the outcome in slow head-on collisions while net erosion dominates for fast off-axis collisions. The dependence on impact parameter is almost as important as the dependence on impact speed. Off axis collisions can result in fast-spinning elongated remnants or contact binaries while fast collisions result in smaller fragments overall. Clumping of debris escaping from the post-collision remnant can occur, leading to the formation of smaller rubble piles.; Results are presented from a dozen direct N-body simulations of terrestrial planet formation with various initial conditions. In order to increase the realism of the simulations and investigate the effect of fragmentation on protoplanetary growth, a self-consistent planetesimal collision model was developed that includes fragmentation and accretion of debris. The collision model is based on the rubble-pile planetesimal model developed and investigated in the parameter space studies summarized above.; I have also looked to the small bodies currently in our solar system to help constrain its evolution. Understanding the dynamics and evolution of these objects will also place constraints on the initial conditions of planet formation models. I present a new code (companion) that identifies bound systems of particles in O (N log N) time. The method is applied to data from asteroid satellite simulations (Durda et al. 2004) and previously unknown multi-particle configurations are noted. (Abstract shortened by UMI.)...