Jay Melosh

Part 1 of 2 by colleagues Marc W. Caffee, Timothy D. Swindle, and Elizabeth (Zibi) P. Turtle H. Jay Melosh passed away on September 11, 2020 in Cape Cod, Massachusetts. Jay’s research career spanned five decades, during which time he served on the faculty at Caltech, SUNY Stonybrook, University of Arizona, and Purdue University. Jay’s research interests were diverse and influential. His work on the geophysics of impact processes revolutionized understanding of not only the impact processes themselves, but the important roles impacts have played in the evolution of the solar system, Earth, and the development of life. Jay was born on June 23, 1947 in Patterson, New Jersey and grew up in nearby Ridgewood. He completed his elementary schooling at New Hampton High School in New Hampshire, but not before shattering multiple windows from a chemistry experiment gone awry, a harbinger of his later research in the shattering and explosive effects of impacts. He earned a Bachelor’s degree (Magna Cum Laude) in physics from Princeton University in 1969. He then attended Caltech from 1969 to 1972, earning his PhD in Physics and Geology. His research advisor was Nobel laureate Murray Gell-Mann. Although Jay published a highly cited paper on quarks in 1974, during his time as a research associate at the Enrico Fermi Institute at the University of Chicago his passion was geophysics. In 1976 Jay took his first faculty appointment at Caltech, where he worked until 1979. During this time Jay explored the role of impacts in determining the orientation of the Moon as well as the relationship between the Moon’s orientation and mascons, concentrations of denser material beneath the lunar surface that cause an increase in the local gravitational pull. Jay continued to study these enigmatic features and more recently was a member of the scientific team associated with the GRAIL lunar spacecraft, which confirmed in greater detail the link between these mass concentrations and the impact cratering process. Jay left Caltech in 1979 for SUNY Stonybrook where he was an Associate Professor of Geophysics for three years. In 1982, Jay joined the Planetary Sciences faculty at the University of Arizona, working there until 2009. During this time Jay continued groundbreaking research in the nature and effects of impacts on Earth, and other planetary bodies, literally writing the book on "Impact Cratering" in 1989. Together with his students and postdoctoral researchers, he explained how impacts on Mars could deliver meteorites to Earth, explored details of how Earth’s Moon could have been formed by a giant impact 4.5 Gyr ago, and performed detailed theoretical calculations that led to a more complete understanding of the Chicxulub impact, the event that led to the disappearance of dinosaurs 66 million years ago. In 2009, Jay moved to Purdue University, where he built a planetary science group within the Earth, Atmospheric, and Planetary Sciences Department. During his time at Purdue University, Jay and his students continued investigations of impact processes and other geophysical phenomena. His work spanned a wide variety of celestial objects: Earth and its Moon, Mercury, Venus, Mars, Pluto, comets, and giant planet satellites including Callisto, Ganymede, Europa, Titan, Miranda. Jay viewed his role as an educator and mentor with great enthusiasm. Jay advised over 20 graduate students who ultimately received PhDs in the disciplines of geology, planetary science, and physics. Jay also sponsored many undergraduate students, helping them early in their careers to explore what it meant to be a scientist. Although his training was in theoretical physics and geophysics, Jay had a deep passion for geologic field studies and the lessons that could be learned about planetary processes by studying analogs here on Earth. Jay relished field trips, and with a Socratic, and at times irreverent, approach that drew students into the excitement of exploration and discovery on their own, he led numerous trips to nearby sites such as Meteor Crater and the Pinacate Volcanic Field, as well as sites further afield like the Channeled Scablands and Yellowstone. His field trips at Arizona were legendary. While the development of geologic field expertise was the priority, these trips were seldom without high adventure, much to the dismay of university officials responsible for the repair of vehicles damaged or sacrificed for the sake of learning. Late in his tenure at Arizona, a survey of alumni about the curriculum revealed that many of them viewed Jay’s field trips as the most valuable learning experience they had in graduate school. His understanding of geologic processes and his ability to explain them in terms that not only educated but engaged students, and his colleagues, was unique. Jay encouraged students to take scientific chances, not to be afraid to consider new ideas or to revisit old ideas that had previously been overlooked. He considered school a time to explore and to make the most of opportunities, even if not directly related to one's research. Jay's love of learning, of questioning established wisdom (often with a mischievous grin), and of searching for answers to mysteries – new or old – were inspiring and exemplified just how much fun scientific investigation can be. He modeled this in his own career. His studies on the mechanisms for launching meteorites from Mars led to a long-standing interest in the possibility of life-forms being exchanged between the two planets. He served on a panel of senior scientists reviewing selected UFO reports, a panel that concluded in 1998 that while there was no evidence of extraterrestrial visitations, there was sufficient evidence that there could be “unusual phenomena currently unknown to science” that would certainly be worth studying. continued....