Academic and Professional Appointments: 1966, Fellow, Lick Observatory 1967-1968, Postdoctoral Research Fellow, Kellogg Radiation Laboratory, California Institute of Technology 1968-1972, Assistant Professor of Astronomy, University of Texas at Austin 1970-1977, Consultant, Jet Propulsion Laboratory, Pasadena, California 1972-1982, Consultant, NASA Headquarters, Washington, DC 1972-1986, Consultant, Lawrence Livermore National Laboratory, Livermore, California 1972-1975, Associate Professor, Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 1973 National Academy of Sciences Exchange Scientist to the USSR O. Yu. Schmidt Institute of Geophysics, Moscow) 1975- Professor, Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 1977, Acting Director, Lunar and Planetary Laboratory, and Acting Head, Department of Planetary Sciences, University of Arizona 1978-1981, Director, Lunar and Planetary Laboratory, and Head, Department of Planetary Sciences, University of Arizona