Sagan, Carl Edward

(b. 9 November 1934 in Brooklyn, New York; d. 20 December 1996 in Seattle, Washington), astronomer and Pulitzer Prize-winning author whose visibility as a television personality made him one of the most recognized scientists of the twentieth century.

Sagan was the first of two children born to Samuel Sagan, a garment cutter, and Rachel Molly Gruber, a homemaker. Both parents were Jewish immigrants to Brooklyn. A family visit to the 1939 New York World’s Fair sparked Sagan’s interest in science. By adolescence, he was an aficionado of science fiction and had resolved to become an astronomer. The family moved to Rahway, New Jersey, about 1948. After graduating from Rahway High School in 1951, Sagan attended the University of Chicago (B.A., 1954, with honors; B.S. in physics, 1955; M.S. in physics, 1956). He did graduate work at the university’s Yerkes Observatory in Williams Bay, Wisconsin, earning a Ph.D. in astronomy and astrophysics in 1960. At the University of Chicago, Sagan met Lynn Alexander, a fellow student, whom he married in 1957. Later that year they established a residence in Madison, Wisconsin. They had two children. The couple were argumentative and often miserable, and they divorced in 1964.

While attending the university, Sagan also met such prominent scientists as the geneticist Hermann Muller, the chemist Harold Urey, the planetary astronomer Gerard Kuiper, and the geneticist Joshua Lederberg. All became friends and mentors. Lederberg was to play a particularly crucial role in Sagan’s career. As a proponent of “exobiology” (the study of life beyond the earth), Lederberg recognized that the space program would bring this speculative field into the realm of positive science. Sagan fully shared Lederberg’s enthusiasm for exobiology. After the Soviet Union’s 1957 launching of Sputnik, Lederberg helped Sagan obtain a post as experimenter on the National Aeronautics and Space Administration’s (NASA) Mariner missions to Venus. This was the first of a string of scientific and advisory roles with the space agency that Sagan held throughout his career.

The most important part of Sagan’s doctoral thesis concerned the planet Venus. Some had suggested that the cloud-shrouded planet had oceans and life. Opposing this view were microwave readings implying that the planet was far too hot for liquid water, yet the planet’s proximity to the sun could not itself account for such high temperatures. Sagan explained the measured high temperatures as the consequence of a greenhouse effect, in which atmospheric gases prevented thermal radiation from escaping efficiently into space. The idea was not new, and no definitive model was then possible, but Sagan became a leading advocate of the model, which was ultimately proved correct.

Sagan occupied posts as Miller Research Fellow at Berkeley (1960–1962) and Visiting Assistant Professor of Genetics at Stanford (1962–1963). In 1961, he was the youngest of the eleven scientists attending the Green Bank meeting organized by the radio astronomer Frank Drake. The meeting’s subject was the possibility of radio communication with extraterrestrial intelligent life-forms. Those in attendance estimated the number of intelligent species in the galaxy using the latest thinking on the origin of life. They came up with an estimate of between 1,000 and 100 million technologically advanced species. The meeting helped spur serious efforts to pick up interstellar signals.

Sagan moved east to Cambridge, Massachusetts, to accept a position as lecturer and assistant professor of astronomy at Harvard (1962–1968), also working as a researcher at the Smithsonian Astrophysical Observatory. At Harvard his attention turned to the planet Mars, then considered by many (including Sagan) to be a plausible abode of life. The principal evidence for life on Mars was the planet’s seasonal changes. Telescopic observers had long reported that the planet’s dark regions appeared to darken or expand during the Martian summer and lighten or contract in the winter. Sagan’s teacher Kuiper theorized that this was the result of seasonal growth and decline of vegetation. Sagan provided a convincing nonbiological explanation. In a model developed with his colleague James Pollack, he argued that the dark regions were Martian highlands. Seasonal winds blow light-colored dust into the highlands, covering the darker rock and changing its telescopic appearance; in the opposite season, the wind scours the highlands of dust, uncovering the dark rock. Sagan was one of the few American scientists to cultivate U.S.-Soviet ties throughout the cold war. He wrote Intelligent Life in the Universe (U.S. publication, 1966) with a prominent Soviet astrophysicist, I. S. Shklovskii.

In 1968, Sagan married Linda Salzman; they had one son. In his personal life Sagan was charismatic, egotistical, and occasionally temperamental. A workaholic, he was often an inattentive father. Sagan was politically liberal and spoke out on human rights issues privately and publicly. He supported the legalization of marijuana, which he used and credited for some of his scientific inspirations.

Sagan was passed over for tenure at Harvard. His former mentor Harold Urey gave him a scathingly negative review, faulting his penchant for speculation at the expense of solid results. Frustrated by his stalled advancement, Sagan accepted a post in 1968 as associate professor of astronomy and space sciences at Cornell University in Ithaca, New York, where he spent the rest of his career. He become full professor of astronomy and space sciences in 1971 and occupied an endowed chair, the David Duncan Professorship of Astronomy and Space Sciences. Sagan was also director of Cornell’s Laboratory for Planetary Studies and (from 1968 to 1979) editor in chief of the journal Icarus. In his years at Cornell, Sagan became an influential figure at NASA. In 1969 Sagan and his colleague Frank Drake helped design a plaque, carried aboard the Pioneer spacecraft, containing a symbolic message to hypothetical extraterrestrials that might find it.

In a 1972 article in Science, Sagan and George Mullen proposed a gradually declining greenhouse effect as a way of resolving the “faint sun paradox.” Astrophysical considerations imply that the primordial sun must have been much fainter and cooler than it is today, yet the geologic record suggests that the earth has always been warm enough to have liquid water, which is presumably a condition for life. Sagan’s original and quantitative analysis of the issue was highly influential.

Sagan meanwhile played a key role in NASA’s 1976 Viking lander mission to Mars. He served on the imaging team that designed and operated a camera capable of taking panoramic color images from the Martian surface—probably Viking’s single most important instrument. Sagan also had close ties with the teams devising instruments for the detection of microbial life and served as a publicist for the mission through his television appearances. Viking was a resounding success: both landers set safely down and returned impressively detailed photographs and other data. The biology instruments were confused by an unexpectedly active surface chemistry. Ultimately, their results were judged not to support the existence of life. That was a disappointment to Sagan (who had not discounted the possibility of creatures large enough to photograph).

In the 1970s Sagan launched a second career as popularizer of science. He became a fixture of space-related news coverage and popular talk shows. He was a master of the sound bite; even his distinctive enunciation commanded attention. Sagan’s 1977 book The Dragons of Eden: Speculations on the Evolution of Human Intelligence won a Pulitzer Prize. The jury called it “as easily a work of philosophy as it is of science.” After his work with the Viking mission, Sagan turned his attention to Cosmos (1980), a graphically innovative television series and book deftly blending astronomy, cultural history, and informed speculation. Cosmos became the highest-rated series ever made for American public television. Winning both Emmy and Peabody Awards, it eventually was seen by a reported half billion viewers in sixty nations. But Sagan often found himself the focus of colleagues’ misgivings about the popularization of science. Such attitudes led to a veto of Sagan’s 1992 election to the National Academy of Sciences.

Ann Druyan, a collaborator on the Cosmos series, became Sagan’s third wife. They married in 1981, a month after Sagan’s bitter divorce from Salzman became final. This third marriage was the happiest and produced two children. Sagan’s later works include a novel, Contact (1985), which was made into a 1997 motion picture; Shadows of Forgotten Ancestors: A Search for Who We Are (with Ann Druyan, 1992); and The Demon-Haunted World: Science as a Candle in the Dark (1996). In the latter book Sagan was a skeptical but open-minded critic of such popular obsessions as UFOs, alien abductions, and paranormal phenomena.

In 1980 Sagan cofounded the Planetary Society, the largest space-interest organization in the world. He was an activist for social and education issues and nuclear arms reduction. In a 1983 article written with four colleagues for Science, he claimed that the smoke and dust of a nuclear war would result in a catastrophic cooling of the global climate whose effects might approach those of the nuclear detonations themselves. These claims of “nuclear winter” were bitterly contested both by political opponents and by specialists who charged that estimates had been skewed in order to produce the dire predictions. In the late 1980s, with funding from the filmmaker Steven Spielberg, Sagan and the physicist Paul Horowitz collaborated on a full-sky survey intended to detect any interstellar signals from extraterrestrial beings. It found no repeating signals within its range of sensitivity. Sagan died of complications from myelodysplasia, a bone marrow disease. He is buried at Lakeview Cemetery in Ithaca.

Sagan is best remembered for his skill in bringing science to the masses. His gift for language and his ease before the television cameras rarely have been equaled by a working scientist. Sagan’s public career has tended to overshadow his scientific achievements, which were nonetheless varied and numerous (more than 300 scientific articles). The most personal phase of Sagan’s research comprised his diverse attempts to establish the existence of extraterrestrial life. Of all the talented people drawn to exobiology in the early years of the space age, Sagan alone pursued the field in all its varied aspects. In all cases, of course, the results were negative. But Sagan tested ideas of fundamental importance held by many of the best scientists of his time. We are left with a universe in which life seems rarer than many had supposed at the start of the space age. As Sagan himself maintained, that, too, is worth knowing.

The principal biographical sources are Keay Davidson, Carl Sagan: A Life (1999) and William Poundstone, Carl Sagan: A Life in the Cosmos (1999), both of which contain extensive bibliographies. Daniel Cohen, Carl Sagan: Superstar Scientist (1987), written for young readers, was the only book-length biography published in Sagan’s lifetime. From the 1970s onward, Sagan’s career was covered extensively in the general press. Particularly notable are Henry S. F. Cooper, Jr.’s two-part profile for the New Yorker, “A Resonance with Something Alive” (21 June 1976): 39–83 and (28 June 1976): 30–61 and two pieces by Timothy Ferris (or Rolling Stone, “A Conversation with Carl Sagan of the Mars Mariner Project” (7 June 1973): 26–30, and “The Odyssey and the Ecstasy” (7 Apr. 1977): 56–65. There is an obituary in the New York Times (21 Dec 1996).

William Poundstone