Geology's Cassidy tripled the world’s meteorite collection

Emeritus Professor William A. Cassidy of the Department of Geology and Environmental Science in the Dietrich School of Arts & Sciences — creator of the Antarctic Search for Meteorites (ANSMET) program in 1976 and its primary investigator for nearly 20 years — died March 25, 2020.

Bruce Hapke, a department geophysicist who arrived with Cassidy in 1967 and retired in 2001, just a few years after him, had the office next door and spent many a lunch together. Hapke recalled Cassidy as “a very kind person and thoughtful. He was very considerate, and he had a kind of unique gift: If two people were discussing something and they started to argue, he would be able to come up with just the right sentence and diffuse the situation. It made him a good leader.

“He was a good friend and a good scientist,” Hapke added. “He was a meticulous observer and researcher and he mentored his students well.”

Cassidy’s greatest impact came with ANSMET, Hapke said. Learning that a Japanese team had discovered several meteorites on the Antarctic ice and theorizing that glacier movement and subsequent wind erosion of the ice was exposing meteorite falls from disparate times and locations, Cassidy received National Science Foundation funding over many years to explore the area. His own team recovered more than 22,000 meteorite samples, tripling the world's meteorite collection. Some of his finds were later discovered to be pieces from the moon and Mars.

In recognition of his work, Antarctica’s Cassidy Glacier was named for him, as well as the mineral Cassidyite and an asteroid, 3382 Cassidy. He recounted his work in a 2003 Cambridge University Press memoir, “Meteorites, Ice, and Antarctica: A Personal Account.”

Cassidy also spent years studying the impact craters left by meteorites, particularly in Argentina, where about 20 clustered craters were left from a large iron meteorite that had broken up in mid-air. Employing local people to help with the excavation, Cassidy received another NSF grant to uncover a 13-ton iron meteorite, one of the largest iron meteorites in the world, which the Argentine government subsequently turned into the center of a national park.

One meteorite, however, eluded Cassidy, Hapke said. Searching through the records of the original Spanish conquerors of what would become Argentina, Cassidy noticed their sighting of “a mountain of fire” that had fallen from the sky. It must have arrived during the same meteorite shower that produced the 20 craters, Cassidy surmised. But he could never find this other impact area. “He said, ‘How can you lose a meteorite that big?’” Hapke remembered. “But he never did find the ‘mountain of fire.’ He figured the Spaniards melted it down for weapons or something.”

Another departmental colleague, William Harbert, who joined Pitt in 1989, remembered Cassidy as “a world-class scientist” and instructor. “His teaching was really exceptional. He was a very popular teacher. Any time people saw him or his office door was open, people were welcome to walk in, and he was always focused on what they were talking about.

“He was just a voice of common sense, very good natured as a mentor for me and giving me advice” as a fellow faculty member, Harbert said. “He was someone who was extremely generous with his time, focusing on what needed to be done and what the path forward was – what was best collectively.

“He had a very wry sense of humor,” he added. “It’s the kind of sense of humor you see in field geologists who have spent a lot of time in remote field areas.”

According to a department memorial statement, Cassidy graduated from the University of New Mexico with a bachelor’s degree in geology and earned his Ph.D. in geochemistry from Penn State University, where he met his wife, Beverly, at Penn State. They had three children, Shauna, Laura and Brian.

— Marty Levine