July 18, 2005

Dr. Carl Edward Sagan Accomplishments

By Dr. Frank J. Collazo



Sagan, Carl Edward (1934-1996), was an American astronomer who popularized science and tried to make it more accessible to the public.  Sagan’s research spanned many areas of astronomy, cosmology, and the philosophy of science, but he was especially interested in the origin of life on Earth and in the possibility of life elsewhere in the universe.  He also worked to bring science to the public through lectures, television shows, and popular books.


Sagan was born in New York City.  He earned his bachelor’s degree in physics at the University of Chicago in 1955 and went on to obtain his doctoral degree in astronomy and astrophysics from the university in 1960.  Sagan started college at age sixteen, earning four degrees including a Ph.D. by the time he was twenty-six.  He received more than twenty honorary degrees before his death in 1996.


From 1960 to 1962 he served as a research fellow at the University of California in Berkeley.


From 1962 to 1968 he lectured at Harvard University and did research at the Smithsonian Astrophysical Laboratory, both in Cambridge, Massachusetts.


In 1968 Sagan moved to Cornell University in Ithaca, New York to become the director of the new Laboratory for Planetary Studies.


In 1970 he became a professor of astronomy and space science at Cornell, a position he held until his death.


While Sagan was completing his doctoral degree, he became involved with the planetary exploration programs of the National Aeronautics and Space Administration (NASA).  He advised the agency on the Mariner, Pioneer, Voyager, and Galileo missions to other planets from the 1960s through the 1990s.


He helped design the plaques carried by the Pioneer 10 and 11 spacecraft, plaques that depicted human life and Earth's location in the solar system.


Organic Modules: Recent experiments and calculations, including some carried out in astronomer Carl Sagan's lab at Cornell University in Ithaca, New York, have demonstrated that fairly complex organic molecules, including amino acids could survive if a comet crashed into Earth.  Thus, meteorites that fell to earth during the waning stages of the great bombardment may have imported the building blocks of life.


The technical challenges of actually detecting Earth-like planets are not insurmountable, and once a candidate had been seen, several things could be learned about it.  Suppose an astronomer 40 light-years away had detected our Earth—it would be, in American astronomer Carl Sagan's phrase, a “pale blue dot” seeming very close to a star (our sun) that outshines it by many million times.


Venus Planetary Surface Research: In the early 1960s, Sagan did his first major research on the planetary surface and atmosphere of the planet Venus.  At the time, many scientists believed that the surface of Venus might have moderate temperatures that humans could endure.  Measurements of radiation from Venus seemed to show that even Venus’s dark side was nearly 300°C (nearly 600°F).  However, proponents of a temperate Venus argued that some process in the atmosphere or in the space very near Venus might make the planet look hotter than it was.  Sagan showed that none of these ideas matched observable data as well as the idea that Venus’s surface is actually very hot.  He also created mathematical models of Venus’s atmosphere, taking into account the way he expected the atmosphere to trap the sun’s heat.  These models showed that the radiation from Venus probably presented an accurate measurement of the surface’s temperature—far too hot for humans to endure.


In the 1980s Carl Sagan, in writing his novel Contact (later made into a major motion picture of the same name), consulted the Caltech theoretician Kip Thorne to see if a wormhole could transport his heroine from one place in the universe to another. Physicists had previously calculated that the throat connecting the two ends of a wormhole would pinch off too quickly for anything to pass through.  But following Sagan’s question, Thorne and a student figured out that a theoretical kind of matter, which they call “exotic matter,” might be able to keep the throat open. This type of matter cannot exist in our current understanding of the constituents of the universe, but new laws of physics may be discovered that permit it.


Terra Forming: In a scenario, first put forward by astronomer Carl Sagan in 1961 (he later rescinded it) Venus—covered in sulfuric acid and poisonous carbon dioxide—would be bombarded by bacteria that would slowly transform the atmosphere and create oxygen.  Cooling and “the Big Rain” would follow, and hardy Earthlings could in time colonize the overheated planet.  Recently, Mars has become the favorite candidate for terra forming, since it appears to have abundant supplies of ice and possibly even water.


Research on Earth Gas Components: Later in the 1960s, Sagan built on the work of American chemists Stanley Miller and Harold Urey.  In the 1950s Miller and Urey had combined methane, ammonia, water vapor, and hydrogen, the probable components of Earth's early atmosphere, in a flask.  They introduced electrical sparks into the mixture to simulate lightning.  When they analyzed the contents of the flask, they found that the chemicals had combined to form amino acids and hydroxy acids, the building blocks of the proteins in living things.  Sagan followed a similar method, but refined the primordial soup mixture to include methane, ammonia, water, and hydrogen sulfide.  He also exposed the mixture to ultraviolet light to simulate the effect of sunlight on the chemicals.  His mixture produced amino acids as well as several kinds of sugars and nucleic acids.  Nucleic acids are fundamental substances of life, responsible for passing on genetic characteristics and triggering the formation of specific proteins.  The work of Urey, Miller, and Sagan showed that the chemicals present on the early Earth could combine under the right conditions to form the building blocks of life.


Mariner 9 Spacecraft-Mars Voyage:  In the late 1960s, Sagan helped show that the variations in color on the surface of the planet Mars were not caused by the presence of life.  Earlier observers of Mars had suggested that the dark, greenish areas might be vegetation of some sort.  Sagan proposed that the dark areas were hills, which the Martian wind stripped of the finer, lighter-colored dust particles that collected in the valleys.  Sagan’s theory was confirmed by the Mariner 9 spacecraft’s visit to Mars.


Self-Replicating Module: Dr. Carl Sagan, professor of astronomy at Harvard University, stated in 1963 that laboratory synthesis of a self-replicating molecule is only a short time away.  He suggested two approaches to the subject.  The first is a simulation experiment of the type in which several microorganisms are introduced into a simulated Martian atmosphere.  A study is made of the survivors.  The second approach is the direct search for life on Mars.  Dr. Sagan's procedure is to subject Mars to infrared spectrometry to detect the presence of microorganisms on the planet.  He feels that the planet Jupiter may also support life, and that life on the moon is possible.


Nuclear Winter: During the 1970s, Sagan studied the present atmosphere of Earth.  He studied the way that winds circulated dust through the atmosphere and how large amounts of dust, such as that from volcanic explosions, might affect Earth’s climate.  His study of Earth’s atmosphere led him to formulate the idea of nuclear winter with American scientists Paul and Anne Ehrlich in the 1980s.  Sagan and the Ehrlichs theorized that the dust and ash thrown into the atmosphere by the explosions of a nuclear war and the ensuing fires might be so thick and widespread that it would block the Sun’s light for months or years.  The damage that a nuclear winter would cause to crops and Earth’s ecosystems would be at least as devastating as the nuclear explosions.  The idea of nuclear winter was met with much controversy, and scientists have continued debating the theory.

Nuclear Weapons Effects:  Carl Sagan and other scientists have suggested that the use of explosives delivered by planetary missiles believe that this approach was fraught with danger.  Sagan and others were concerned that the nuclear weapon might not work, or that the launch might fail and cause the weapon to fall back to Earth.  Another concern was that a country might use nuclear weapons to intentionally divert a small asteroid toward an enemy nation for warlike purposes.

Nuclear Issues: The Nevada Test Site, where the federal government conducts underground nuclear explosions, including those for the Strategic Defense Initiative ("Star Wars") program, was busy this year.  The entrance to the site, which employed 8,300 people, was the scene early in the year of numerous nonviolent antinuclear demonstrations that drew such well-known figures as astronomer Carl Sagan and actor Martin Sheen.

Educating the Public: Throughout his life, and especially in the latter part of his life, Sagan sought to bring science to the public.  He gave many public lectures and wrote books for the public, as well as technical papers.  He testified at a congressional hearing on the future of space exploration.

Pulitzer Prize: He won the 1978 Pulitzer Prize for his book The Dragons of Eden: Speculations on the Evolution of Human Intelligence.

Published Books: Other popular books include Broca’s Brain: Reflections on the Romance of Science (1979), the novel Contact (1985), Pale Blue Dot (1994), and The Demon-Haunted World (1996).  In 1980 Sagan co-wrote and hosted Cosmos, a very popular 13-part television series, for the Public Broadcasting Service.  A movie based on his novel, Contact, was released in 1997, a few months after his death.

Television Series: On the Set of Cosmos, American astronomer Carl Sagan was best known for his ability to bring science and astronomy to a general audience.  He wrote many books for the general public and hosted the television series Cosmos in 1980.


Extraterrestrial Intelligence: In 1983, Astronomy Life on Other Worlds, and The Search for Extraterrestrial Intelligence, or SETI, once again has the approval of the U.S. government.  In 1981, Senator William Proxmire won passage of legislation that temporarily prohibited the National Aeronautics and Space Administration from spending money on such a program, which can involve the use of radio telescopes to hunt for radio wave patterns that might be evidence of intelligent life on other worlds.  But a pro-SETI campaign conducted by many scientists eventually persuaded him to drop his opposition.


In March a private SETI project began its own search, using a small radio telescope at Harvard, Mass.  The effort was funded by the Planetary Society, an organization founded by Cornell University astronomer and SETI proponent Carl Sagan.  The recognition of SETI as a respectable scientific endeavor has been slow in coming.  The idea has been around for over 160 years, but not until 1982 did the prestigious International Astronomical Union establish a commission dedicated to such efforts.  This search "is, by any standards, a long shot," said Sagan. If it is successful, however, the social and scientific consequences will be profound.


Quick Facts about Carl Edward Sagan, American Astronomer, Author, and Educator:



November 9, 1934


December 20, 1996

Place of Birth

New York City, New York

Known For

Popularizing science through his lectures, television series, and books


Exploring the possibility of extraterrestrial intelligence


Late 1950s-1990s.  Served as an advisor on all of NASA's main planetary missions


1960.  Received his Ph.D. in astronomy and astrophysics from the University of Chicago


Early 1960s.  Supplied the theoretical model that proved Venus's surface is extremely hot; his conclusions were verified by later NASA missions to Venus


1960s.  Built on and expanded previous work done by American chemists Stanley Miller and Harold Urey on the origin of life on Earth


1968.   Joined Cornell University as director of the Laboratory for Planetary Studies


1970.  Became professor of astronomy and space science at Cornell University


1976.  Was appointed to the position of David Duncan Professor of Astronomy and Space Sciences at Cornell University


1978.  Received the Pulitzer Prize for general non-fiction, for his book The Dragons of Eden, which explores the brain and human intelligence


1980.   Co wrote and hosted the 13-episode public television series Cosmos


Co founded the Planetary Society, which under his leadership became the largest space-interest group in the world


Studied possible atmospheric effects of nuclear war and formulated the nuclear winter theory in collaboration with American scientists Anne and Paul Ehrlich


1994.  Received the Public Welfare Medal, the highest award of the National Academy of Sciences


Sagan helped design the interstellar messages carried by the Pioneer 10, Pioneer 11, Voyager 1, and Voyager 2 spacecraft.


Over half a billion people in sixty countries watched Sagan's public television series Cosmos.








Carl Sagan Biography, Microsoft ® Encarta ® Reference Library 2004. © 1993-2003 Microsoft Corporation.  All rights reserved.


Carl Sagan on the Set of Cosmos, Microsoft ® Encarta ® Reference Library 2004. © 1993-2003 Microsoft Corporation.


Quick Facts about Carl Edward Sagan, Microsoft ® Encarta ® Reference Library 2004. © 1993-2003 Microsoft Corporation.


Asteroids, Comets, and Earth.  Stephen P. Maran is an astronomer and editor of the Astronomy and Astrophysics Encyclopedia.


History of Predicting the Future.  Brian Horrigan is exhibit curator for the Minnesota Historical Society and the author, with Joseph Corn, of Yesterday's Tomorrows: Past Visions of the American Future (1984, reprinted 1996).


Questions and Answers.  Astronomer Jay Pasachoff, Microsoft ® Encarta ® Reference Library 2004.  © 1993-2003 Microsoft Corporation.


Science Fiction.  David G Hartwell and Kathryn E Cramer, Microsoft ® Encarta ® Reference Library 2004.  © 1993-2003 Microsoft Corporation.


Extra Terrestrial Life, Microsoft ® Encarta ® Reference Library 2004. © 1993-2003 Microsoft Corporation.