The ozone layer shields us from cancerous ultraviolet radiation. Understanding how it is being destroyed was the mission of more than 350 scientists from the United States, Canada, Europe, Japan, and Russia; 19 of the researchers came from Harvard. The exploration included the first high-altitude reconnaissance flights over Russia since the Soviet Union shot down Gary Powers in a U-2 spy plane in 1960. The flights in 2000 were made by a National Aeronautics and Space Administration ER-2 aircraft, a civilian version of the U-2. These sorties were part of the largest international effort to date to measure ozone in this hemisphere. “We want to learn enough about the polar vortex to predict what’s going to happen there over the next decade,” said James Anderson, Weld Professor of Atmospheric Chemistry in the Harvard Faculty of Arts and Sciences and one of two mission scientists directing the ER-2 flights.