James B. Pollack; Leading Planetary Scientist

James B. Pollack, 55, luminary among the world’s planetary scientists who helped formulate the theory of nuclear winter. Pollack discovered that Venus’ clouds are made of sulfuric acid and his work led to the discovery that Saturn’s rings are made of ice chunks. But he was best known for the nuclear winter theory. He, mentor Carl Sagan and three colleagues theorized that airborne soot from a nuclear war would block the sun’s rays and drop temperatures below freezing worldwide. The theory was widely disputed and the scientists later conceded that they had overestimated the severity of a potential nuclear winter. Pollack joined NASA’s Ames Research Center in 1970 and won the center’s greatest distinction when he was named an Ames Fellow. The New York native, who was educated at Princeton, UC Berkeley and Harvard, played a key role in many NASA planetary spacecraft missions, including the Viking and Voyager projects. Among his other endeavors was the study of volcanoes’ effect on climate. On Monday in San Jose of spinal cancer.