Carl Sagan Biography

World of Physics on Carl Sagan

Born in 1934 in New York City, Carl Edward Sagan earned his bachelor's and doctoral degrees from the University of Chicago. He conducted research and lectured at the University of California in Berkeley and Harvard University. In 1970, he became the David Duncan Professor of Astronomy and Space Science at Cornell University in Ithaca, New York. He died in 1996 at age 62, having established himself as an insightful researcher, but in particular as arguably the greatest popularizer of astronomy of the twentieth century. For his signal achievements in bringing astronomy into the popular limelight, Sagan was honored with the American Astronomical Society's Annenberg Prize in 1992.

Throughout his career, Sagan's work centered on studying planetary atmospheres, especially the conditions on Earth that gave birth to early life forms. In this area, Sagan made his greatest contributions to science.

Sagan began his research, however, on the surface and atmosphere of Venus. In the early 1960s, it was thought that the surface of the planet was relatively cool, despite conflicting data on radiation emissions that put the temperature at 600K. Based on radar and optical observations, he was able to calculate the height of the clouds on Venus and account for the "greenhouse effect" that raised surface temperature to that of the emissions data.

Next, Sagan turned his energies to simulating the primordial atmosphere of Earth in an effort to duplicate the conditions that supported early life on our planet. Similar to the earlier experiments of Stanley Miller and Harold Urey, Sagan was able to produce amino acids, the building blocks of DNA, by irradiating a methane, ammonia, water, and hydrogen sulfide mixture. He also found five-carbon sugars, which form nucleic acids, glucose, and fructose--essential to life processes--as well as adenosine triphosphate (ATP), which stores energy in living cells. From his 1963 discovery, scientists can now conjecture that life on earth arose when complex nucleic acids and proteins formed, using the chemical energy stored in the oceans.

Sagan pushed for planetary exploration that launched the Viking probes that landed on Mars and the Voyager probes that took photographs of Jupiter and Saturn. In 1966, he discovered mountains and cliffs on the surface of Mars using reflecting radar. From information about the planet's dust storms collected in Mariner 9's 1971-72 voyage, he hypothesized that, on Earth, a nuclear war would put clouds of dust and debris in the atmosphere and keep out sunlight, resulting in a nuclear winter. He became a vocal critic of nuclear weaponry, although he did support the use of radioactive sources, such as plutonium, to power interplanetary spacecraft in the far reaches of the solar system. He also found evidence of organic molecules in Jupiter's atmosphere.

A Pulitzer Prize-winning author, Sagan wrote over a dozen books and 400 published scientific articles. He popularized the science of astronomy with several books that deal with planets and the evolution of life, strongly supporting the view that life exists on other planets. He served as the editor of the main astronomical journal devoted to planetary astronomy, Icarus, and his 1980 television series "Cosmos" and book of the same name was a runaway hit. In the final years of his life, Sagan's wide-ranging mind turned to the problem of how atmospheric temperature is affected by volcanic activity.