The auroras over Hawaii on the night of July 8, 1962, were unlike any that humans had ever witnessed. “N-Blast Tonight May Be Dazzling; Good View Likely,” read a headline in the Honolulu Advertiser beforehand. Nine seconds after 11 P.M., a startling flash set the sky aglow like eerie daylight, slowly fading from green to yellow to orange before settling on a vivid, unsettling red.
The U.S. had just detonated a thermonuclear bomb 100 times more powerful than the one dropped on Hiroshima. Launched on a missile from Johnston Atoll, a U.S. unincorporated territory between the Marshall Islands and Hawaii, the bomb exploded at 250 miles above Earth’s surface—around the altitude in low-Earth orbit of most modern-day satellites. This event, called Starfish Prime, wasn’t the first or last time that the U.S. or Soviet Union tested nuclear weapons in space (there were more than a dozen tests between 1958 and 1962), but it was the most impactful. The blast generated a power surge over the Pacific Ocean that knocked out about 300 streetlights on the island of Oahu—and destroyed or damaged about a third of the roughly two dozen satellites then in orbit.
"The Starfish Prime shot is sort of the poster child for why we don’t like nukes blowing up in space,” says Jonathan McDowell, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian. Indeed, only a few years later, in 1967, both the U.S. and the Soviet Union signed on to the Outer Space Treaty, which forbade putting weapons of mass destruction in orbit.
Now, some six decades after the last nuclear detonation in Earth orbit, the threat of another has emerged with the Department of Defense warning about a potential Russian program to place a nuke in space. When the United Nations Security Council recently put forward a resolution to reaffirm the ban on such weapons, Russia vetoed the measure. U.S. officials have said there is no “imminent danger” because no warheads are known to be in space. But they have deemed the prospect “deeply troubling” because a nuclear detonation there today would be far more destructive than even Starfish Prime.
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