William (Bill) R. Ward passed away on September 20th at his home in Prescott, Az after a battle with brain cancer. Ward was a preeminent theoretician that made many seminal contributions to our understanding of planetary dynamics and solar system formation. With his thesis advisor, Peter Goldreich, Ward proposed that planetesimals were formed via local gravitational instability in the protostellar disk. In 1973, Ward was the first to recognize that the obliquity of Mars undergoes large oscillations, and with Alastair Cameron in 1976, he was one of the original proposers of the giant impact theory for the origin of the Moon. Ward was a pioneer in the study of gravitational interactions between planets and their precursor gas disk, and how these may cause large scale changes in planetary orbits. His many papers on this topic elucidated the nature of Type I vs. Type II migration, central to our understanding of planet formation in our Solar System and in exoplanetary systems. Ward also contributed greatly to our understanding of satellite formation and dynamical evolution. After completing his PhD at Caltech, Ward worked as a post-doc at CFA, before moving to JPL. He joined SwRI in Boulder, Co., in 1998, and retired from SwRI as an Institute Scientist in 2014. Ward is survived by his wife Sandra, brother Jeff,sister Patty, sons Brad and Scott, and daughter Stephanie.
Robin Canup
Southwest Research Institute