Science: The Cosmic Explainer

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Sagan published his first paper at 22. Its title was an echo from his days with Muller and a sign of his growing interest in exobiology: "Radiation and the Origin of the Gene." A key point was that radiation may have been the trigger for the combination of the first DNA molecules. Eventually some 300 more papers would follow, including a particularly brilliant bit of deduction about the planet Venus. At the time, many scientists still regarded Venus as a kind of sister planet of the earth with a benign climate. But radio emissions from the planet were hinting at puzzlingly high temperatures. Sagan pointed out that a Venusian atmosphere of carbon dioxide and water vapor would trap solar heat, create a "greenhouse effect" and raise surface temperatures far above those of the earth. His prediction was soon confirmed by Soviet landers. The planet's surface temperature proved to be about 480° C (900° F), high enough to melt lead.

In 1960, Sagan headed for the University of California at Berkeley, where he spent two years as a research fellow; he insisted on taking a turn at teaching a class, even though the terms of his contract did not require it. At the Stanford University School of Medicine he delved into the origins of life. Then he went off to teach and do research at Harvard and the Smithsonian Astrophysical Observatory in Cambridge, Mass.

Collaborating with his first graduate student, James Pollack, he offered a novel explanation for the periodic lightening and darkening of parts of Mars' surface. Some scientists had suggested that the changes were due to seasonal variations in plant life. Sagan and Pollack argued that the fluctuations were varying dust patterns kicked up by winds of ferocious force. Years later, closeup photos of Mars confirmed their thesis.

At Harvard, Sagan was a highly popular lecturer, talking about such things as UFOs (he debunked them) and the idea of extraterrestrial life (he promoted it). He was divorced from Lynn (after two children, Dorian, now 21, and Jeremy, 19) and married to Linda Salzman, an artist. His career appeared to be taking off. But in spite of his professional flair, Harvard never offered him tenure. So, in 1968, when Cornell University beckoned with an offer to set up a laboratory of planetary studies, he promptly accepted it and moved to rural Ithaca, N. Y.

Even Sagan's scientific friends acknowledge that he does not have the patience or persistence for the slow, painstaking experimentation and data collection that is at the heart of the scientific process. Nor has he come close to the kind of breakthrough work that wins Nobel Prizes. But he more than compensates with other significant talents. He has a penchant for asking provocative questions. Sometimes, as Sagan fully concedes, this can rile others. But such prodding can inspire students and colleagues, lead to brilliant new insights and generally create a mood of intellectual excitement.

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