An American geophysicist specializing in impact cratering, after earning a degree in physics at Princeton Jay earned a doctorate in physics and geology from Caltech in 1972. His research interests included impact craters, planetary tectonics, and the physics of earthquakes and landslides. His most recent research included study of the giant-impact origin of the moon. He was active in astro-biological studies, which relate to the exchange of microorganisms between the terrestrial planets.

In 2008 the American Geophysical Union awarded him the Harry H. Hess medal for outstanding achievement in research in the constitution and evolution of Earth and its sister planets. Asteroid 8216 Melosh was named in his honor. His recognition, honors, and awards were many and varied and a reflection of his leadership and international reputation.

Jay is survived by his wife, Ellen Germann, an accomplished weaver; sons Nick and his wife, Jill; and Greg and his wife, Carmen; five grandchildren; and Ellen’s four grandchildren who also looked to Jay as their granddad.