Sagan, Carl (1934-1996)

American astronomer

One of the first scientists to take an active interest in the possibility that life exists elsewhere in the Universe, and an astronomer that was both a best-selling author and a popular television figure, Carl Sagan was one of the best-known scientists in the world. Sagan made important contributions to studies of Venus and Mars, and he was extensively involved in planning NASA's Mariner missions. Regular appearances on the Tonight Show with Johnny Carson began a television career that culminated in the series Sagan hosted on public television called Cosmos, seen in sixty countries by over 400 million people. He was also one of the authors of a paper that predicted drastic global cooling after a nuclear war; the concept of "nuclear winter" affected not only the scientific community, but also national and international policy, as well as public opinion about nuclear weapons and the arms race. Although some scientists considered Sagan too speculative and insufficiently committed to detailed scientific inquiry, many recognized his talent for explaining science, and acknowledged the importance of the publicity generated by Sagan's enthusiasm.

Sagan was born in Brooklyn, New York, the son of Samuel Sagan, a Russian emigrant and a cutter in a clothing factory, and Rachel Gruber Sagan. He became fascinated with the stars as a young child, and was an avid reader of science fiction, particularly the novels by Edgar Rice Burroughs about the exploration of Mars. By the age of five, Sagan was sure he wanted to be an astronomer, but, as he told Henry S.F. Cooper, Jr., of the New Yorker, he sadly assumed it was not a paying job; he expected he would have to work at "some job I was temperamentally unsuited for, like door-to-door salesman." When he found out a few years later that astronomers actually got paid, he was ecstatic. "That was a splendid day," he told Cooper.

Sagan's degrees, all of which he earned at the University of Chicago, include an A.B. in 1954, a B.S. in 1955, an M.S. in physics in 1956, and a doctorate in astronomy and astrophysics in 1960. As a graduate student, Sagan was deeply interested in the possibility of life on other planets, a discipline known as exobiology. Although this interest then was considered beyond the realm of responsible scientific investigation, he received important early support from scientists such as Nobel laureates Hermann Joseph Muller and Joshua Lederberg. He also worked with Harold C. Urey, who had won the 1934 Nobel Prize in chemistry and had been Stanley Lloyd Miller's thesis adviser when he conducted his famous experiment on the origin of life. Sagan wrote his doctoral dissertation, "Physical Studies of the Planets," under Gerard Peter Kuiper, one of the few astronomers at that time who was also a planetologist. It was during his graduate student days that Sagan met Lynn Margulis, a biologist, who became his wife in 1957. The couple had two sons before divorcing in 1963.

From graduate school, Sagan moved to the University of California at Berkeley, where he was the Miller residential fellow in astronomy from 1960 to 1962. He then accepted a position at Harvard as an assistant professor from 1962 to 1968. On April 6, Sagan married the painter Linda Salzman; Sagan's second marriage, which ended in a divorce, produced a son. From Harvard, Sagan went to Cornell University, where he was first an associate professor of astronomy at the Center for Radiophysics and Space Research. He was then promoted to professor and associate director at the center, serving in that capacity until 1977, when he became the David Duncan Professor of Astronomy and Space Science.

Sagan's first important contributions to the understanding of Mars and Venus began as insights while he was still a graduate student. Color variations had long been observed on the planet Mars, and some believed these variations indicated the seasonal changes of some form of Martian plant life. Sagan, working at times with James Pollack, postulated that the changing colors were instead caused by Martian dust, shifting through the action of wind storms; this interpretation was confirmed by Mariner 9 in the early 1970s. Sagan also suggested that the surface of Venus was incredibly hot, since

the Venusian atmosphere of carbon dioxide and water vapor held in the sun's heat, thus creating a version of the "greenhouse effect." This theory was also confirmed by an exploring spacecraft, the Soviet probe Venera IV, which transmitted data about the atmosphere of Venus back to Earth in 1967. Sagan also performed experiments based on the work of Stanley Lloyd Miller, studying the production of organic molecules in an artificial atmosphere meant to simulate that of a primitive Earth or contemporary Jupiter. This work eventually earned him a patent for a technique that used gaseous mixtures to produce amino acids.

Sagan first became involved with spaceflight in 1959, when Lederberg suggested he join a committee on the Space Science Board of the National Academy of Sciences. He became increasingly involved with NASA (National Aeronautics and Space Administration) during the 1960s, and participated in many of their most important robotic missions. He developed experiments for the Mariner Venus mission and worked as a designer on the Mariner 9 and the Viking missions to Mars, as well as on the Pioneer 10, the Pioneer 11, and the Voyager spacecrafts. Both the Pioneer and the Voyager spacecrafts have left our solar system carrying plaques which Sagan designed with Frank Drake as messages to any extraterrestrials that find them. The plaques contain pictures of two humans, a man and a woman, as well as various astronomical information. The nude man and woman were drawn by Sagan's second wife, Linda Salzman, and they provoked many letters to Sagan denouncing him for sending "smut" into space. During this project Sagan met the writer Ann Druyan, the project's creative director, who eventually became his wife. Sagan and Druyan had two children.

Sagan continued his involvement in space exploration in the 1980s and 1990s. The expertise he developed in biology and genetics while working with Muller, Lederberg, Urey, and others, is unusual for an astronomer, and he extensively researched the possibility that Saturn's moon, Titan, which has an atmosphere, might also have some form of life. Sagan was also involved in less direct searches for life beyond Earth. He was one of the prime movers behind NASA's establishment of a radio astronomy search program that Sagan called CETI, for Communication with Extra-Terrestrial Intelligence.

A colleague of Sagan's working on the Viking mission explained to Cooper of the New Yorker that this desire to find extraterrestrial life is the focus of all of Sagan's various scientific works. "Sagan desperately wants to find life someplace, anyplace—on Mars, on Titan, in the solar system or outside it. I don't know why, but if you read his papers or listen to his speeches, even though they are on a wide variety of seemingly unrelated topics, there is always the question 'Is this or that phenomenon related to life?' People say, 'What a varied career he has had,' but everything he has done has had this one underlying purpose." When Cooper asked Sagan why this was so, the scientist had a ready answer. "I think it's because human beings love to be alive, and we have an emotional resonance with something else alive, rather than with a molybdenum atom."

During the early 1970s Sagan began to make a number of brief appearances on television talk shows and news programs; Johnny Carson invited him on the Tonight Show for the first time in 1972, and Sagan soon was almost a regular there, returning to discuss science two or three times a year. However, it was Cosmos, which Public Television began broadcasting in 1980, that made him into a media sensation. Sagan narrated the series, which he wrote with Ann Druyan and Steven Soter, and they used special effects to illustrate a wide range of astronomical phenomena such as black holes. In addition to being extremely popular, the series was widely praised both for its showmanship and its content, although some reviewers had reservations about Sagan's speculations as well as his tendency to claim as fact what most scientists considered only hypotheses.

Sagan was actively involved in politics; as a graduate student, he was arrested in Wisconsin for soliciting funds for the Democratic Party, and he was also involved in protests against the Vietnam War. In December, 1983, he published, with Richard Turco, Brian Toon, Thomas Ackerman, and James Pollack, an article discussing the possible consequences of nuclear war. They proposed that even a limited number of nuclear explosions could drastically change the world's climate by starting thousands of intense fires that would throw hundreds of thousands of tons of smoke and ash into the atmosphere, lowering the average temperature ten to twenty degrees and bringing on what they called a "nuclear winter." The authors happened upon this insight accidentally a few years earlier, while they were observing how dust storms on the planet Mars cooled the Martian surface and heated up the atmosphere. Their warning provoked a storm of controversy at first; their article was then followed by a number of studies on the effects of war and other human interventions on the world's climate. Sagan and his colleagues stressed that their predictions were only preliminary and based on certain assumptions about nuclear weapons and large-scale fires, and that their computations had been done on complex computer models of the imperfectly understood atmospheric system. However, despite numerous attempts to minimize the concept of a nuclear winter, the possibility that even a limited nuclear war might well lead to catastrophic environmental changes was supported by later research.

The idea of nuclear winter not only led to the reconsideration of the implications of nuclear war by many countries, institutions, and individuals, but it also produced great advances in research on Earth's atmosphere. In 1991, when the oil fields in Kuwait were burning after the Persian Gulf War, Sagan and others made a similar prediction about the effect the smoke from these fires would have on the climate. Based on the nuclear winter hypothesis and the recorded effects of certain volcanic eruptions, these predictions turned out to be inaccurate, although the smoke from the oil fires represented about 1% of the volume of smoke that would be created by a full-scale nuclear war.

In 1994, Sagan was diagnosed with myelodysplasia, a serious bone-marrow disease. Despite his illness, Sagan kept working on his numerous projects. His last book, The Demon-Haunted World: Science as a Candle in the Dark, was published in 1995. At the time of his death, Sagan was co-producing a film version of his novel Contact. His partner in this project was his wife, Ann Druyan, who had co-authored Comet. Released in 1997, the film received popular and critical acclaim as a testimony to Sagan's enthusiasm for the search for extraterrestrial life. Sagan, who lived in Ithaca, New York, died at the Fred Hutchinson Cancer Research Center in Seattle in 1996.

Carl Sagan won a Pulitzer Prize in 1978 for his book on evolution called The Dragons of Eden. He also won the A. Calvert Smith Prize (1964), NASA's Apollo Achievement Award (1969), NASA's Exceptional Scientific Achievement Medal (1972), NASA's Medal for Distinguished Public Service (twice), the International Astronaut Prize (1973), the John W. Campbell Memorial Award (1974), the Joseph Priestly Award (1975), the Newcomb Cleveland Prize (1977), the Rittenhouse Medal (1980), the Ralph Coats Roe Medal from the American Society of Mechanical Engineers (1981), the Tsiolkovsky Medal of the Soviet Cosmonautics Federation (1987), the Kennan Peace Award from SANE/Freeze (1988), the Oersted Medal of the American Association of Physics Teachers (1990), the UCLA Medal (1991), and the Mazursky Award from the American Astronomical Association (1991). Sagan was a fellow of the American Association for the Advancement of Science, the American Academy of Arts and Sciences, the American Institute for Aeronautics and Astronautics, and the American Geophysical Union. Sagan was also the chairman of the Division for Planetary Sciences of the American Astronomical Society (from 1975 to 1976) and for twelve years was editor-in-chief of Icarus, a journal of planetary studies.