William R. Ward

Southwest Research Institute, Boulder, Colorado ~Institute Scientist, Department of Space Studies. Worked with Peter Goldreich to explain how planetary accretion evolves from cold, condensed dust grains to gravitationally active planetesimals. With A. G. W. Cameron, first advanced the idea that the Moon was born in a giant impact from a Mars-sized object. Predicted the obliquity variations of Mars and linked them to climatic oscillations and the layered terrain in Mars's polar regions. More recently, made contributions to the interactions between growing planets (and the Moon) and the massive disks from which they formed, explaining how many extrasolar planets came to orbit so close to their stars. Among the first to advance the widely accepted theory of planet migration early in solar system history. Contributed to understanding how the excitation of collective motions in the accretion disk by a planet's gravitational field affects the evolution of the planet's orbital size and eccentricity. Clarified the consequences of resonance sweeping, currently the leading candidate for explaining the late heavy bombardment of the planets by projectiles from both the outer solar system and the asteroid belt. Most recently, developed with Robin Canup a new inflow model for the formation of giant-planet satellite systems.~