June 13: Nuclear Winter

James B. Pollack, an astrophysicist and planetary scientist who posited with Carl Sagan and three other scientists the possibility of “nuclear winter” — an environmentally disastrous period following a nuclear war — died on this date in 1994 at age 55. Pollack discovered that Venus’ clouds are made of sulfuric acid, and it was his work that led to the discovery that Saturn’s rings are made of ice chunks. He also investigated the extinction of dinosaurs and the possibilities of terra-forming Mars. An out gay man, Pollack joined NASA’s Ames Research Center in 1970 and played a key role in NASA’s Viking (Mars) and Voyager (interstellar) missions. The nuclear winter theory predicted that nuclear explosions would throw dense smoke into Earth’s upper atmosphere, blocking the absorption of sunlight and causing surface temperatures to drop dramatically.

“Models made by Russian and American scientists showed that a nuclear war would result in a nuclear winter that would be extremely destructive to all life on Earth; the knowledge of that was a great stimulus to us, to people of honor and morality, to act in that situation.” —Mikhail Gorbachev