Whipple, Fred Lawrence (1906-) was an American astronomer who was the first to suggest that the nucleus of a comet resembled a “dirty snowball.” His research led to insights regarding the behavior of meteors and the nature of the upper atmosphere and helped establish the modern view of comets.
Although Whipple made contributions in a number of areas, he was best known for his work with comets. He earned the nickname “Mr. Comet” and was considered the leading authority on the subject. In 1950, he published a landmark paper in the Astrophysical Journal on the composition of comet nuclei. Prior to this time, astronomers believed that comets resembled “floating sand banks” made up of loose particles, with no distinct body. Whipple argued that comets were more like icy conglomerates, or dirty snowballs, composed of ice water, ammonia, methane, and dust.
In 1986, Whipple's prediction was put to the test when Halley's Comet crossed Earth's orbit. Spacecraft equipped with imaging equipment and cameras were launched to get a close-up look at the comet's nucleus. Based on the measurements and photographs obtained from the space probes, researchers confirmed Whipple's “dirty snowball” model for comet nuclei.
In addition to his comet research, Whipple investigated meteors, planetary nebulae, and the evolution of the solar system. Although he officially retired in 1977, he continued with his research five days a week at his Cambridge, Massachusetts, office. At age 92, he became the oldest researcher to ever take part in a NASA mission when he joined the science team working on NASA's Comet Nucleus Tour (Contour). The unmanned Contour spacecraft was supposed to fly past comets Encke and Schwassmann-Wachmann 3 and bring back images of the comets as well as an analysis of the dusts and gases in the nuclei. However, contact with the spacecraft was lost six weeks after its launch.
Whipple's accomplishments include a number of inventions. During World War II (1939–1945), he invented a chaff-cutter, which was used to create tiny pieces of aluminum foil that could be dropped from planes to confuse the enemy's radar. In the 1940's, he devised a bumper, now known as the Whipple shield, to protect spacecraft from meteors. The device is used on nearly all spacecraft.
Whipple was the son of Henry Lawrence and Celestia (MacFarland) Whipple. When Whipple was 15, his family moved from their Iowa farm to California, where he completed high school. He then attended Occidental College. After completing a year at Occidental, he transferred to the University of California at Los Angeles (UCLA) and studied mathematics. In his junior year, he switched his major to astronomy. He graduated in 1927 and then attended the University of California at Berkeley. After earning his Ph.D. degree in astronomy in 1931, he left California and moved to Cambridge, Massachusetts, where he accepted a staff position at the Harvard College Observatory.
Whipple's first job at Harvard was checking the accuracy of photographic plates of the sky. To make the task more interesting, he inspected the photographic negatives for comets. In the course of this work, he discovered six comets, all of which now bear his name.
Early in his career, Whipple set out to learn more about meteors. To accomplish this, he devised a two-station photographic method to measure the trajectory of meteors. Using cameras with rotating shutters, Whipple took photographs of meteors at different locations. He then studied the photographic plates to determine the meteors' atmospheric drag, velocity, and orbit around the sun. Whipple continued this research until it was interrupted by World War II (1939–1945). From his research he theorized that comets were related to meteors and had a similar composition. This line of reasoning helped him formulate the idea that comet nuclei were like dirty snowballs.
In 1932, Whipple was appointed instructor in astronomy at Harvard University, advancing to lecturer six years later. During World War II, he worked on war-related research at the Harvard Radio Research Laboratories, earning a Presidential Certificate of Merit in 1948. At the war's end in 1945, Whipple returned to Harvard where he was named associate professor. Five years later he was promoted to professor, a position he held until 1977 when he retired as Phillips Professor of Astronomy Emeritus. During his Harvard tenure, he also served as chairman of the department of astronomy.
After his meteor research, Whipple studied the orbit of 40 comets to solve a problem that puzzled scientists. Astronomers were uncertain why some comets increase their orbits while others lose energy and decrease their orbits. Whipple suggested that the composition of the nucleus offered an explanation. When the comet is away from the sun and in the coldness of space, it resembles a frozen ice ball. But as a comet nears the sun, the ice begins to melt. When the ice layer evaporates. it causes gases and particles in the ice to fly away from the sun. This “jet” of gas forms the comet's coma (cloudy atmosphere) and tails. Over time, this process results in the comet losing material. Comets with large nuclei are able to withstand repeated passages around the sun, but small-nucleus comets disintegrate more quickly than would be ordinarily predicted. This explains why certain comets fail to appear when expected.
Whipple contributed to the space age in the 1950's when he developed a worldwide network of professional and amateur observers to track satellites. In 1957, when the Soviets launched Sputnik, the first satellite, Whipple's volunteers observed it and reported on the satellite's orbit.
From 1955 to 1973, Whipple was director of the Smithsonian Astrophysical Observatory (SAO), a bureau of the Smithsonian Institute. At the time he took the position, the organization was based in Washington, D.C. One of his first duties was to help move the headquarters to Cambridge, Massachusetts. In 1973, the SAO merged with the Harvard College Observatory to become the Harvard-Smithsonian Center for Astrophysics (CfA). That same year, Whipple became senior scientist at the organization.
In the 1960's, he codeveloped the Multiple Mirror Telescope on Mount Hopkins, near Amado, Arizona. The instrument was made up of six large telescope mirrors functioning as one, and was the first of its kind. In 1982, the Arizona facility was renamed the Fred Lawrence Whipple Observatory. The observatory, which is part of the CfA, contains one of the largest mirror telescopes in the United States.
Whipple was awarded a number of honors throughout his long and distinguished career. He received six Donahue Medals in recognition of the six comets he discovered. Other awards include the J. Lawrence Smith Medal of the National Academy of Sciences in 1949, the Kepler Medal of the American Association for the Advancement of Science in 1971, and the Distinguished Federal Civilian Service Award from President John F. Kennedy in 1963. He died in Cambridge, Massachusetts on August 30, 2004.