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Gordon H. Pettengill (1926–2021)

Pettengill, former director of Arecibo Radio Observatory and principal investigator on NASA’s Pioneer Venus and Magellan missions, led some of the first radar studies of planetary surfaces.

Published onDec 31, 2022
Gordon H. Pettengill (1926–2021)

Pioneering radar astronomer Gordon Hemenway Pettengill left our community on Saturday May 8, 2021, succumbing to congestive heart failure at his home in Concord, Massachusetts. He was 95.

Born on February 10, 1926, in Providence, Rhode Island, Pettengill spent his childhood in Dedham, Massachusetts. As a child he initially planned on a career as an electrical engineer, bolstered by what became a lifelong interest in amateur ham radio. He later recounted unsuccessfully attempting to build radios from spare parts at age six, eventually finding success with a simple crystal set at age 11 or 12 (Pettengill 2005). He was educated at Dedham Country Day School and a Waltham, Massachusetts boys’ school before attending the historic Roxbury Latin School for one year. While he enrolled at MIT at age 16 as a physics major (where he joined the MIT Radio Club), he was drafted into the U.S. Army two years later, serving as an infantryman in France. After the war he was able to put his radio experience to work, working in Austria in the Signal Corps until 1946 (Pettengill 2005).

After completing his undergraduate degree in 1948 he worked as a health physicist at Los Alamos National Laboratory and completed a Ph.D. at the University of California-Berkeley, completing a thesis on proton-proton scattering under Owen Chamberlain (Pettengill 1954). He reflected in his Whitten award speech how in graduate school he felt like a “very small fish in a very large pond” of nuclear physics, and intentionally made the switch to a “younger and less mature field where there might be less competition” ([1], 420). When he brought up his desire to become involved with exploring the solar system using spacecraft in his job interview for the MIT Lincoln Laboratories the Director scoffed “You don’t believe in that Buck Rogers stuff, do you?” ([1], 420). Fortunately, Pettengill proved the more prescient in this conversation.

Pettengill began his radar work at the Millstone Hill facility at the Haystack Observatory complex of MIT’s Lincoln Laboratories, where he started observing Venus in 1958. By 1961 he had made preliminary measurements of the rotational period of Venus and determined that the planet had a “relatively smooth rocky surface” [2]. But much of his early work with Millstone centered on mapping the moon’s surface, beginning in 1960 [3]. In 1967–8 he was part of Irwin Shapiro’s team that utilized the 120-foot Haystack antenna at MIT to measure the delay times of sun-grazing radar pulses bounced off Mercury and Venus as a test of General Relativity [4].

He joined Cornell’s Arecibo Observatory as Associate Director at its opening in 1963, where he remained through the end of 1965. He returned to the facility in 1968 as Director, spending two years in that role before becoming professor of planetary physics at MIT. He served as Director of MIT Center for Space Research from 1984–9. At MIT he continued to use the Haystack facilities as well as Arecibo and eventually the Very Large Array to study various solar system objects.

In an interview Pettengill described his Arecibo research highlights as his high precision measurements of the rotation of Venus and Mercury and the “surface scattering properties” and “surface heights” of sections of Mars (Pettengill & Craft, Jr. 2010). For example, in 1965 observations by Pettengill and Rolf Dyce demonstrated that Mercury is not in synchronous rotation (88 days), but instead has a period of rotation of 59 days, leading to the realization that it instead is in a 3:2 spin-orbit coupling [5].

In the late 1970s he realized his dream of using the ‘Buck Rogers’ technology of spacecraft-mounted radar, serving as PI of the radar altimetry instrumentation on Pioneer Venus in 1977 and scientific radar PI for the Magellan mission to Venus in the 1990s. His work on Pioneer Venus resulted in a groundbreaking topographic map of 93 percent of the Venusian surface to resolution better than 150 km, while Magellan bested that accomplishment, yielding a 100 meter per pixel map of 98 percent of the nearest planet. While Pettengill retired from MIT as professor emeritus in 1995, he afterwards served as PI of a study using the Mars Orbiting Laser Altimeter of the Mars Global Surveyor to analyze a variety of Martian cloud types (1997–2001).

Pettengill was elected to the National Academy of Science in 1979 and was a fellow of the American Academy of Arts and Sciences. He received the 1995 Fred Whipple award of the Planetology Section of the American Geophysical Union (AGU) and the AGU’s Charles A. Whitten Medal in 1997. He served on numerous IAU Divisions and Commissions and was President of Commission 16 Physical Study of Planets & Satellites (1970–3) and Vice-President of Commission 17 The Moon (1967–70). Asteroid 3831 Pettengill honors him. He also received the Magellanic Premium of the American Philosophical Society for his work on Venus in 1994, the oldest American medal for scientific achievement, a “gold medal to be awarded from time to time under prescribed terms, to the author of the best discovery or most useful invention relating to navigation, astronomy, or natural philosophy.” 


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