Fred Lawrence Whipple

Fred Lawrence Whipple (November 5, 1906 – August 30, 2004) was an American astronomer, who worked at the Harvard College Observatory for more than 70 years. Among his achievements were asteroid and comet discoveries, the "dirty snowball" hypothesis of comets, and the invention of the Whipple shield.

Fred Lawrence Whipple was born on November 5, 1906, in Red Oak, Iowa. His parents were farmers. His father, Harry Lawrence Whipple, was of English ancestry; his mother, Celeste MacFarland Whipple, was of Scottish and Irish ancestry. Harry Whipple served as an elder in a Presbyterian church. Fred's younger brother died when he was four. When Fred was 15, the family moved to Long Beach, California, where his father opened a grocery store. An early bout with polio ended his ambition of being a professional tennis player. Whipple studied at Occidental College in Southern California, but after one semester there he transferred to the University of California at Los Angeles where he majored in mathematics, graduating in 1927. Recollecting his path from mathematics to astronomy, Whipple stated in a 1978 autobiography that his "mathematics major veered [him] through physics and finally focused on astronomy where time, space, mathematics, and physics had a common meeting ground."

Whipple became bored with mathematics, and after taking a class in astronomy, taught by Frederick C. Leonard, he enrolled at the University of California, Berkeley where he obtained a PhD in Astronomy in 1931, working in the Lick Observatory. He became interested in comet orbits calculations, which was a long and difficult process at the time. His first published result was the calculation of the 29P/Schwassmann–Wachmann orbit. In 1930, he helped to map the orbit of the then newly discovered planet Pluto. Whipple's thesis was on the cepheid variables, titled A Spectrophotometric Study of the Cepheid Variables η Aquilae and δ Cephei. The measurements he got were 3 times larger than theoretically possible under the Cepheid period-luminosity law; Whipple concluded that the theory "had to be wrong". He did not try to formulate new theory, he later said that it "simply disgusted him".

Whipple joined Harvard College Observatory in 1931. From 1950 until 1977 he was a professor of Astronomy at Harvard University, including being the Phillips Professor of Astronomy between 1968 and 1977, succeeding Cecilia Payne-Gaposchkin. In his early years in Harvard, Whipple was interested in galaxies, and soon published "color indices for 38 galaxies in the Coma-Virgo region, confirming an earlier suggestion that galaxies were redder than average stars of corresponding spectral type". He wanted to continue these studies, but the then director Harlow Shapley "did not welcome competition in galactic studies". Whipple published several articles together with Cecilia Payne-Gaposchkin in 1935 and with Jesse Greenstein in 1937. When Whipple read an article by Ernst Öpik on comets and meteors he became interested in determining meteor trajectories. Whipple developed a "photographic tracking network" to observe meteors in 1936-1937, which continued as the Harvard Photographic Meteor Program. In 1955, he established the Harvard Radio Meteor Project. In 1960s, he showed that most meteors originate within the Solar System rather than from interstellar space, and have comet-like trajectories.

In 1933, Whipple discovered the periodic comet 36P/Whipple and the asteroid 1252 Celestia, which he named after his mother. The official naming citation was mentioned in The Names of the Minor Planets by Paul Herget in 1955 (H 115). He also discovered or co-discovered five other non-periodic comets, the first of which was C/1932 P1 Peltier-Whipple, while his last was C/1942 X1 (Whipple–Fedtke–Tevzadze). In 1939 he also discovered BT Mon, a ninth-magnitude nova "on a spectrum plate taken by Bart Bok".

During World War II, he invented a device for cutting aluminum tinfoil into chaff, a radar countermeasure; his device "would turn 3 ounces of aluminum foil into 3000 half-wave dipoles, and he also found optimum aspect ratios for the foil strips that would work over a range of radar frequencies". Brian G. Marsden called the device "essentially a type of lawn mower". For this invention, Whipple was called the "Chief of Chaff", and was awarded a Certificate of Merit in 1948. In 1946, Whipple invented a "meteoroid bumper", now known as "Whipple shield", a device to protect spacecraft from impact by small particles by breaking them up, eleven years before the first artificial satellite, Sputnik 1, was launched into space.

After the war, the US Army experimented with German V-2 rockets, inviting Whipple to take part in test flights from White Sands Missile Range. There, he befriended Wernher von Braun. Both men "promoted an understanding of space matters by the public", and wrote several popular articles about space exploration for the Collier's together. One article was about a crewed flight to the Moon; by their estimates, it "could happen within 25 years". In another article Whipple proposed to put a telescope into space.

In 1950, Whipple wrote a series of influential papers entitled A Comet Model, published in the Astrophysical Journal, where he proposed the "icy conglomerate" hypothesis of comet composition (later called the "dirty snowball" hypothesis). Criticized at first, the hypothesis was mostly confirmed when ESA's Giotto photographed the Halley's Comet in 1986. Before Whipple, it was believed that comets "were balls of sand held together by gravity". Whipple was best-known for his work on comets, and was even nicknamed Dr. Comet by the press. Whipple's articles on comets were called "the most-cited works in the Astrophysical Journal during the past half century". In 1986 he was one of the guests at the Space Research Institute during the Halley's comet Vega program flybys.