Peter Gierasch, 1940–2023

Peter J. Gierasch

Peter Gierasch, an astronomer at Cornell University whose mathematical models unveiled the turbulent vortices, tempestuous eddies, and atmospheric tumult arising on other worlds — long before spacecraft could consistently prove it with images — died on January 20, 2023, in Ithaca, New York, at the age of 82.

Gierasch, a professor emeritus of astronomy in Cornell’s College of Arts and Sciences, contributed to a wealth of knowledge on the processes of planetary atmospheres — specifically Mars, Venus, Jupiter, and Saturn’s largest moon, Titan. He served as a team scientist on the Viking, Pioneer, Voyager, Galileo, and Cassini missions for NASA.

“Peter is truly one of the leading people who have developed almost everything we know today about the atmospheres of planets, other than the Earth,” said Joseph Veverka, the James A. Weeks Professor of Physical Sciences emeritus (A&S). Gierasch was known for his amazing mathematical ability. “With models, he could predict things before they were seen, but he did take advantage of observation,” Veverka said. “He was able to explain the strange things that were seen in spacecraft images.”

As a freshly minted Ph.D., Gierasch published a 1968 paper on martian thermal and dynamical structure, which was the first to systematically consider the surface-atmosphere (wind-driven) interaction occurring on Mars and how it fundamentally differed from Earth. Gierasch, Veverka, and the late Cornell astronomer Carl Sagan published a detailed paper on martian winds in 1971 that proved accurate when rovers visited the Red Planet about three decades later.

His next groundbreaking 1975 finding focused on Venus’ atmospheric rotation, where he showed how the planet’s equatorial atmospheric region moved much faster than the rest of the planet’s atmosphere. This process — an angular-momentum surplus that contributes to atmospheric superrotation — is now known as the Gierasch Mechanism. Subsequently, this process was discovered again on the large saturnian moon Titan.

Gierasch’s impact on examining planetary atmospheres was exceptional, according to a citation when he received the 2014 Gerard P. Kuiper Prize, the highest honor bestowed by the Division for Planetary Sciences of the American Astronomical Society. He also examined the atmospheres of giant planets. A 1986 paper looked at temperatures as a function of latitude and altitude on Jupiter, as he inferred the atmospheric circulation that those temperatures required. This led to a theory of belts and zones churning above the clouds in Jupiter’s upper troposphere. NASA’s Juno spacecraft mission to Jupiter — which arrived in 2016 —confirmed the concepts.

Gierasch was born in Washington, DC, on December 19, 1940. He graduated from Wayland High School in Wayland, Massachusetts, just outside Boston. He earned both his bachelor’s degree (1962) and his Ph.D. (1968) from Harvard University. His first academic position was at Florida State University in Tallahassee.

Gierasch joined the Cornell faculty in 1972, and he served for a decade as director of the Cornell Center for Radiophysics and Space Research. He was an Alfred P. Sloan Foundation Research Fellow from 1975 to 1979.

For his 60th birthday celebration at Cornell, the International Astronomical Union formally named an asteroid — 5153 Gierasch — in his honor.

— Text courtesy of Cornell University