Teenagers armed with AK-47s stood guard as Lockheed pilot Ron Williams taxied a NASA research jet down a runway in Punta Arenas at the southern tip of Chile. The long, gliderlike wings of the aircraft—a modified Lockheed U-2 spy plane known as the ER-2—were heavy with fuel and scientific instruments. Not long after he took off, Williams watched as the sky above his cockpit turned from blue to purple to black, with countless bright stars. Below, Earth's curvature appeared. Williams had climbed into the overworld, the heart of the frigid, dry lower stratosphere, some 18 kilometers up.


It was August 1987 and dictator Augusto Pinochet still ruled Chile. Williams had journeyed to Patagonia to help researchers probe a worrying development in the skies over nearby Antarctica: Reactions triggered by industrial chemicals appeared to be eating a hole in Earth's ozone layer, which protects life from harmful ultraviolet (UV) radiation.

The flights were dangerous, recalls atmospheric chemist James Anderson of Harvard University. He had a 150-kilogram instrument aboard the ER-2 that would sniff the overworld's thin air for ozone-destroying chemicals as Williams hurtled, for 8 hours, high over icy nothingness. If the single-engine jet went down, a rescue wasn't certain. And just landing the spindly plane at the notoriously windy Punta Arenas airport could be an adventure. "The worst was the thought that my instrument wouldn't work," Anderson says, "since the pilot was risking their life."

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