Carolyn Shoemaker was a housewife with no science degree when, aged 51, she started searching for comets and asteroids with her astrogeologist husband, Gene Shoemaker. By the time of her death at the age of 92 from a fall, she had established herself as one of the leading hunters of such bodies of her generation.
She found a total of 32 comets and, according to the IAU Minor Planet Center, 377 asteroids, of which 160 were her sole discoveries. Among the comets was one of the most famous of all time, Comet Shoemaker-Levy 9, which crashed into Jupiter in a spectacular display in 1994.
That story had begun 16 months earlier at the Palomar Observatory in California. She stopped scanning her plates to observe: “I do not know what I have, but it looks like a squashed comet.” In fact the comet had already broken up and was a train of fragments heading for its extinction. Shoemaker was not thrilled with this news. “I never lost a comet before,” she said. “All my comets, I knew where they were. But this one I was going to lose.”
The Palomar Asteroid and Comet Survey (Pacs), which Shoemaker joined in 1980, was set up to find comets and asteroids that might pose a threat to civilisation, but the discovery of Shoemaker-Levy 9 by Carolyn, Gene, and David Levy, overshadowed that aim. The impact of the comet with Jupiter was experienced with awe around the world, visible with quite small telescopes and seen live on television.
For the first time many people found themselves pondering the question of what happens when comets hit planets and whether these impacts could have influenced the origin of life on Earth. Appearing on the BBC children’s programme Blue Peter, Shoemaker was asked what would happen if this comet hit the Earth. “We would all die,” was her reply. When it was pointed out that this was for a children’s programme she modified her answer to: “We would all be very uncomfortable.”
The 32 comets Shoemaker had found by 1994 were at the time the largest number ever discovered by one individual. It was patient work and she found one comet for every 100 hours of scanning plates. She received an honorary doctorate of science from the University of Northern Arizona in 1990, the scientist of the year award in 1995 and the Nasa exceptional scientific achievement medal in 1996.
In 1998 the US National Academy of Sciences named the Shoemakers jointly as recipients of the James Craig Watson medal. Asteroid 4446 Carolyn is named after her.
Carolyn was born in Gallup, New Mexico, where her parents, Hazel and Leonard Spellmann, ran a chicken farm. The family moved to Chico, California, where she and her brother Richard grew up. She studied history, political science and English at Chico State University.
At her brother’s wedding in 1950 she met his former Caltech roommate, Gene Shoemaker, who had moved to Princeton to work on his doctorate. They corresponded by letter and both attended a two-week camping trip on the Tennessee Plateau. They were married in 1951 and had three children, Christine, Linda and Patrick.
The Shoemaker family lived in Colorado and California before settling in Flagstaff, Arizona. Her first job was as a schoolteacher, teaching seventh grade, but she tired of this and devoted herself full-time to raising her children. When they had grown up she began studying astronomy and worked as a field assistant for her husband, mapping and analysing meteoritic impact craters.
In 1980 she joined Pacs and was hired as a scientist in the astronomy branch of the US Geological Survey. She used plates taken at the Palomar Schmidt telescope, working with a stereoscope to compare plates taken on different nights to look for moving objects, asteroids or comets.
In 1989 she became an astronomy research professor at Northern Arizona University. Eight years later, while on a trip investigating meteoritic craters in Australia, she and Gene were involved in a car crash. Gene died instantly and Carolyn suffered severe injuries. “Without Gene, I would never have known the excitement of planetary science,” she wrote in an autobiographical essay. “Without me, he often said, his search for asteroids and comets, and then the Australian cratering work, would never have been attempted. Together, we could do more than either of us alone.”
She is survived by her children, three grandchildren and five great-grandchildren.
• Carolyn Jean Spellmann Shoemaker, comet and asteroid hunter, born 24 June 1929; died 13 August 2021