H. Jay Melosh

2008 Harry H. Hess Medal Winner

H. Jay Melosh was awarded the 2008 Harry H. Hess Medal at the AGU Fall Meeting Honors Ceremony, held 17 December 2008 in San Francisco, Calif. The medal is for “outstanding achievements in research in the constitution and evolution of Earth and sister planets.”


Jay is a world-class Earth and planetary scientist. He is responsible for a number of predictions, innovations, and contributions to our understanding of important phenomena in geophysics and planetary physics. Jay is the world’s expert on collisional/cratering processes in the solar system, processes that are perhaps the most important in shaping the planets and other bodies in space.

Jay is an extraordinarily original thinker. Most of Jay’s research in the Earth and planetary sciences has focused on the application of physical principles to the understanding of the forces that shape the surfaces of the Earth and other planets. One of his most original contributions is the process he has called “fluidization,” which is a unified explanation for the paradoxes surrounding the collapse of impact craters, the emplacement of long runout landslides, and the physics of earthquakes.

Jay participated in the analysis of geodetic motions in the Pacific Northwest and in 1983 concluded from these data that the region is not undergoing aseismic subduction, but is in an interseismic interval that must have followed a large prehistoric earthquake. Jay also proposed a viscous flow theory for the origin of the outer rise topography in subduction zones that cured many problems posed by the then current elastic flexure models. Although the community neglected this work for a few years, it was recently revived by Mike Gurnis and his students and is currently the accepted model for how topographic features arise in subduction zones.

Additional examples of Jay’s original thinking include the following:

  1. In 1980 he predicted that meteor-strewn fields would be found on Venus with a characteristic dimension of 20 kilometers. This prediction was verified by Magellan in 1991.
  2. In 1993 he predicted that the Shoemaker-Levy 9 fragments were only a few hundred meters in diameter. After a lot of controversy, this prediction was confirmed in 1995.
  3. In 1997 he predicted that about 50% of fast rotating near-Earth objects would have satellites. This prediction was confirmed by P. Pravek and Al Harris.

Jay has also made major contributions to understanding how meteorites can be ejected from planetary size bodies, the impact origin of the Moon and its implications for the earliest history of the Earth, the mechanism by which the dinosaurs were extinguished, as well as a steady background of contributions to the understanding of impact craters, landslides, and terrestrial tectonics. Jay has written a very well received monograph, Impact Cratering: A Geologic Process, literally “the book” on impact cratering.

Jay has shown unusual breadth in his scientific career. He is a worthy recipient of the Harry H. Hess Medal.

—MICHAEL J. DRAKE, University of Arizona, Tucson


I am very pleased to have been awarded the AGU Harry H. Hess Medal. I thank my official nominator and department head, Mike Drake, as well as those who served on the awards committee and wrote letters of support. I also thank all of those who have served as my mentors, and a large group of students, former students, postdocs, colleagues, and the Department of Planetary Sciences at the University of Arizona. Without all of their support and intellectual stimulation I would have achieved little in my scientific endeavors. The myth of a scientist working in isolation, somehow distilling the nature of the universe in an ivory tower, is widely promulgated as a pleasant fiction. Everyone here knows how wrong this perception is. Science is an intensely social activity and cannot be divorced from personal interactions.

Although I never interacted with Harry Hess scientifically, I benefited greatly from his department at Princeton. I was an undergraduate at Princeton from 1965 to 1969, overlapping his last 4 years there. I met him briefly several times but do not recall any scientific exchanges. Although I was then (and remained) a physics major, I was enraptured by the introductory geology course taught by Ken Deffeyes. Classes with J. C. Maxwell and Sheldon Judson and interactions with Bob Hargraves fed the spark he struck, not to mention many hours spent in the now defunct geology museum in Guyot Hall. Upon arriving at California Institute of Technology for Ph.D. studies in theoretical physics, I continued to pursue geology with Barclay Kamb, Bob Sharp, and Gerry Wasserburg. I spent two wonderful summers on Blue Glacier with Barclay, honed the art of critical thinking in classes and discussions with Gerry, and was introduced into the essential role of field geology by Bob, all while continuing to pursue the physics of quarks. From Murray Gell-Mann, my physics advisor, I took away a lasting appreciation of the value of paradoxes in science. After a brief postdoctoral year at Chicago’s Enrico Fermi laboratory, Barclay and Gerry convinced me to return to Caltech as a junior faculty member in the Division of Geological and Planetary Sciences. Thanks to the efforts, inspiration, and support of these individuals, as well as many others whom I lack space to name, I made the transition from theoretical physics to geological and planetary sciences, a change I have never regretted.

In subsequent years at the University of Arizona, my research directions were strongly influenced by new data appearing on the scientific horizon. Meteorites that seemed to have come from Mars, the Alvarezes’ proposal of a K/T impact, and the idea that the Moon was born in a giant impact all enriched the texture of my research.

Although I cannot disguise the pleasure I feel upon receiving the Hess Medal, the pleasure is only the latest part of the joy I have experienced in participating in a fascinating scientific adventure, an adventure in which many of you present here tonight have been fellow travelers.

—H. JAY MELOSH, University of Arizona, Tucson