Whipple, Fred Lawrence

(b. 5 November 1906 in Red Oak, Iowa; d. 30 August 2004 in Cambridge, Massachusetts), pioneer in twentieth-century astronomy best known for his “dirty snowball” theory, which was later proved correct, that comets are made of ice mixed with some rock.

Whipple was born into a farming family, the only child of Harry Lawrence Whipple and Celestia (MacFarland) Whipple. For the first fourteen years of his life, Whipple lived on his family’s farm in Iowa, where, as Whipple would later recall, he spent most of his time going to school and trapping skunks to make some money. During that time Whipple contracted polio, which essentially put a halt to his dream of becoming a professional tennis player. The family moved to Long Beach, California, in 1920. After graduating from high school, Whipple attended Occidental College from 1923 to 1924 and then enrolled at the University of California, Los Angeles (UCLA). He majored in mathematics because he found the subject easy and it gave him free time to play tennis. Although he repeatedly tried out for the UCLA tennis team, he never made the squad. Following his graduation with a BA in mathematics from UCLA in 1927, Whipple accepted a teaching fellowship at the University of California, Berkeley, and married Dorothy Woods. The couple had one child before they divorced in 1935. Whipple married his second wife, Babette Frances Samuelson, on 20 August 1946; they had two children.

Although he graduated from UCLA as a mathematics major, Whipple had already shifted his focus to astronomy by his junior year at UCLA. He received his PhD in astronomy from the University of California, Berkeley, in 1931 and then headed east to join the staff of the Harvard College Observatory. Whipple’s first assignment at Harvard was inspecting some 70,000 sky survey photographic plates to make sure that the telescopic camera was accurate. Whipple performed this procedure with a handheld magnifier and, in the process of some 1,200 hours of scanning the photographs, discovered six comets. Among those comets is the 36P/Whipple, which was the thirty-sixth known periodic comet. Whipple received the Donohue Medal for these discoveries. His work in the 1930s included using a new, two-station method of photography, which enabled Whipple to determine meteor trajectories. He discovered that almost all visible meteors are composed of fragile material from comets and that none could be proven to come from beyond Earth’s solar system.

During World War II Whipple conducted research in connection with the U.S. military, including working in radar counter measures at the Harvard Radio Research Laboratory. He is credited with co-inventing the chaff-cutter, a device that cut aluminum foil into thousands of fragments, thus confusing enemy radar into reporting many more attacking planes than were really there. He went on in 1946 to invent a “meteor bumper” in anticipation of future space travel. Called the “Whipple shield,” it is a thin outer skin of metal that protects spacecrafts from meteors by causing them to vaporize when they hit the shield. After the war Whipple turned his full attention to comets, using Super-Schmidt meteor cameras set up in New Mexico. His initial research showed that approximately 99 percent of all meteor orbits are elliptical about the sun, with the other 1 percent having unknown orbits.

Most astronomers in the 1940s believed that comets were not discrete bodies but actually interplanetary “gravel banks” held together by gravity as they traveled through space. But Whipple thought that they were actually discrete bodies of ice and dust. In 1950 he published his seminal paper in the Astrophysical Journal, presenting his theory to a wide scientific audience. Whipple had observed that Encke’s Comet, which returns for viewing every 3.3 years, returned half an hour to an hour earlier than predicted, which had led to the theory that the comet might be encountering a resisting medium in space. Whipple realized that the orbit might change slightly through gas vaporization from ices. Furthermore, he stated that no gravel bank could last through 1,000 revolutions around the sun as Encke’s Comet had done. In his landmark paper, he proposed that comets have large, solid nuclei composed of ices, such as water, ammonia, methane, carbon dioxide, or carbon monoxide, which are mixed with other particles. When reporting on this new theory, the popular media referred to it as the “dirty snowball” theory. Although the theory grew to be widely accepted, it was not proven until 1986 with the return of Halley’s Comet. At that time photographs taken by the Giotto spaceship of the European Space Agency showed that the comet had a discrete nucleus roughly the size of New York City.

Whipple continued to work at Harvard throughout his career, acting as director of the Smithsonian Astrophysical Observatory in Cambridge from 1955 until 1973, when it merged with the Harvard Observatory and was renamed the Harvard-Smithsonian Center for Astrophysics. According to the scientist, his greatest honor was receiving the Award for Distinguished Federal Civilian Service from President John F. Kennedy in 1963 for his project of setting up a network of cameras to track satellites. Once again thinking ahead, Whipple and his fellow astronomers had already begun setting up the network through their “Moonwatch” group and were the only ones ready in 1957 to track Sputnik, a satellite launched by the former Soviet Union, which was engaged with the United States in the cold war. Whipple retired from Harvard in 1977, having held numerous posts, including chairman of the astronomy department from 1949 to 1956 and Phillips Professor of Astronomy beginning in 1968. Despite his “official retirement,” Whipple continued to conduct research and publish until he was ninety, bicycling to the observatory at Harvard six days a week. In 1999 the National Aeronautics and Space Administration chose him to work on the Comet Nucleus Tour spaceflight mission, making Whipple the oldest researcher ever to accept such a post. Whipple’s numerous awards included the J. Lawrence Smith Medal of the National Academy of Sciences for research on meteors and the Space Pioneers Medallion for contributions to the Federal Space Program. Whipple died at the age of ninety-seven at a Cambridge hospital after a prolonged illness.

The oldest living astronomer and planetary science pioneer at the time of his death, Whipple, who was known as “Dr. Comet” to his friends, had a profound influence on furthering planetary science. Although best known for his “dirty snowball” theory of comets, Whipple had many research interests that led him to make contributions to numerous fields, including astronomy, satellite tracking, variable stars, supernovas, astronomical instrumentation, and radio astronomy. Whipple’s legacy includes the Fred Lawrence Whipple Observatory on Mount Hopkins in Arizona.

An in-depth profile of the scientist and his achievements is in Notable Scientists: From 1900 to the Present (2001). The author’s reminiscences of his childhood and career are in “Of Comets and Meteors,” Science 289, no. 5480 (4 Aug. 2000): 728. Biographical articles about Whipple include Ken Gewertz, “Fred Whipple: Stargazer,” Harvard University Gazette (18 Oct. 2001), and David H. Levy, “Dr. Comet at 95,” Sky and Telescope 103, no. 1 (Jan. 2002): 89–90. Obituaries are in the New York Times (31 Aug. 2004), the Washington Post (1 Sept. 2004), and Nature 432 (4 Nov. 2004): 31.

David Petechuk