Sagan became a full professor at Cornell in 1971 and directed a lab there. He contributed to most of the unmanned space missions that explored our solar system. He conceived the idea of adding an unalterable and universal message on spacecraft destined to leave the solar system, that could be understood by any extraterrestrial intelligence that might find it. The first message that was actually sent into space was a gold-anodized plaque attached to the space probe Pioneer 10. He continued to refine his designs and the most elaborate such message he helped to develop was the Voyager Golden Record that was sent out with the Voyager space probes.
Sagan was among the first to hypothesize that Titan and Jupiter's moon Europa may possess oceans (a subsurface ocean in the case of Europa) or lakes, making them habitable for life. Europa's subsurface ocean was later indirectly confirmed by the spacecraft Galileo.
Sagan believed that the Drake equation suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations (the Fermi paradox) suggests that technological civilizations tend to destroy themselves rather quickly. This stimulated his interest in identifying and publicizing ways that humanity could destroy itself, with the hope of avoiding such destruction and eventually becoming a space-faring species.
Under the pseudonym "Mr. X," Sagan wrote an essay concerning pot smoking in the 1971 book Reconsidering marijuana. Lester Grinspoon (the book's editor), disclosed this to Keay Davidson, Sagan's biographer. Sagan commented that marijuana encouraged some of his works and enhanced experiences.
From Cosmos and his frequent appearances on The Tonight Show, Sagan became associated with the catchphrase "billions and billions." (He never actually used that phrase in Cosmos, but his distinctive delivery and frequent use of billions made this a favorite phrase of Johnny Carson and others doing the many affectionate impressions of him.) He wrote Pale Blue Dot: A Vision of the Human Future in Space, which was selected as a notable book of 1995 by The New York Times.
Sagan caused mixed reactions among other professional scientists. On the one hand, there was general support for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of skepticism and against pseudoscience. On the other hand, there was some unease that the public would misunderstand some of the personal positions and interests that Sagan took as being part of the scientific consensus rather than his own personal views, and there was some unease, which some believe to have been motivated in part by professional jealousy, that scientific views contrary to those that Sagan took (such as on the severity of nuclear winter) were not being sufficiently presented to the public. His comments on the Kuwait oil well fires during the first Gulf War were shown later to be in error.
Late in his life, Sagan's books developed his skeptical, naturalistic view of the world. In The Demon-Haunted World: Science as a Candle in the Dark, he presented tools for testing arguments and detecting fallacious or fraudulent ones, essentially advocating wide use of the scientific method. In The Demon-Haunted World, Sagan gave a list of errors he had made (including his predictions about the effects of the Kuwaiti oil fires) as an example of how science is self-correcting. The compilation Billions and Billions: Thoughts on Life and Death at the End of the Millennium, published after Sagan's death, contains essays written by Sagan, such as his views on abortion, and Ann Druyan's account of his death as a non-believer.
Sagan was considered by some to have an inflated ego. In 1994, Apple Computer began developing the Power Macintosh 7100. They chose the internal code name "Sagan," in honor of the astronomer. Though the project name was strictly internal and never used in public marketing, when Sagan learned of this internal usage, he sued Apple Computer to use a different project name — other projects had names like "Cold Fusion", and he was displeased at being associated with what he considered pseudoscience. Though Sagan lost the suit, Apple engineers complied with his demands anyway, renaming the project "BHA" (Butthead Astronomer). Sagan sued Apple for libel over the new name, claiming that it subjected him to contempt and ridicule. Sagan lost this lawsuit as well; still, the 7100 saw another name change: it was now called "LAW" (Lawyers Are Wimps).
Sagan has been widely portrayed as an atheist or agnostic, but some have also argued that his views resembled pantheism, citing quotes such as: "The idea that God is an oversized white male with a flowing beard who sits in the sky and tallies the fall of every sparrow is ludicrous. But if by 'God' one means the set of physical laws that govern the universe, then clearly there is such a God. This God is emotionally unsatisfying... it does not make much sense to pray to the law of gravity."
Sagan married three times; the famous biologist Lynn Margulis (mother of Dorion Sagan) in 1957, artist Linda Salzman in 1968, and author Ann Druyan in 1981, to whom he remained married until his death.
The landing site of the unmanned Mars Pathfinder spacecraft was renamed the Carl Sagan Memorial Station in honor of Dr. Sagan on July 5, 1997. Asteroid 2709 Sagan is also named in his honor.
The 1997 movie Contact (see above), based on Sagan's novel of the same name, and finished after his death, movingly ends with the dedication "For Carl."
Sagan, Carl, et. al. Murmurs of Earth: The Voyager Interstellar Record. Random House, 1977
Sagan, Carl et. al. The Nuclear Winter: The World After Nuclear War. Sidgwick & Jackson, 1985
Sagan, Carl and Richard Turco, A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race. Random House, 1990
Sagan, Carl, The Dragons of Eden: Speculations on the Evolution of Human Intelligence. Ballantine Books, December 1989, ISBN 0345346297, 288 pgs
Sagan, Carl, Broca's Brain: Reflections on the Romance of Science. Ballantine Books, October1993, ISBN 0345336895, 416 pgs
Sagan, Carl and Ann Druyan, Shadows of Forgotten Ancestors: A Search for Who We Are. Ballantine Books, October 1993, ISBN 0345384725, 528 pgs
Sagan, Carl and Ann Druyan, Comet. Ballantine Books, February 1997, ISBN 0345412222, 496 pgs
Sagan, Carl, Contact. Doubleday Books, August 1997, ISBN 1568654243, 352 pgs
Sagan, Carl, Pale Blue Dot: A Vision of the Human Future in Space. Ballantine Books, September 1997, ISBN 0345376595, 384 pgs
Sagan, Carl and Ann Druyan, Billions & Billions: Thoughts on Life and Death at the Brink of the Millennium. Ballantine Books, June 1998, ISBN 0345379187, 320 pgs
Sagan, Carl, The Demon-Haunted World: Science As a Candle in the Dark. Ballantine Books, March 1997, ISBN 0345409469, 480 pgs
Sagan, Carl and Jerome Agel, Cosmic Connection: An Extraterrestrial Perspective. Cambridge University Press, January 15, 2000, ISBN 0521783038, 301 pgs
Sagan, Carl, Cosmos. Random House, May 7, 2002, ISBN 0375508325, 384 pgs
Zemeckis, Robert, Contact. Warner Studios, 1997, ASIN 0790736330 IMDB
Davidson, Keay, Carl Sagan: A Life. John Wiley & Sons, August 31, 2000, ISBN 0471395366, 560 pgs
Contact: A Eulogy to Carl Sagan, by Dr. Ray Bohlin, president of Probe Ministries. Dr. Bohlin suggests that the movie Contact can serve as a fitting eulogy for Carl Sagan. Sagan's scientific approach to the question, "was the universe created?" is critically analyzed by Bohlin from his Christian perspective.
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