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EARTH IS IN A CON­STANT GAME OF CE­LES­TIAL BUMPER CARS, COL­LID­ING WITH— and oblit­er­at­ing—the rel­a­tively puny space rocks that dare cross its path. The planet is still stand­ing af­ter 4.6 bil­lion years, but a mod­ern col­li­sion could dev­as­tate cities, con­ti­nents, and even life it­self. (Just ask the di­nosaurs.) NASA’s Cen­ter for Near-Earth Ob­ject Stud­ies keeps watch on more than 18,000 po­ten­tial trou­ble­mak­ers, rang­ing from just 3 feet to more than 3,000 feet across. Me­te­orites smaller than 100 feet usu­ally ex­plode in midair, like one did over Chelyabinsk, Rus­sia, in 2013. There wasn’t enough shrap­nel to leave a crater, but the sonic boom did blast out win­dows. So how much havoc could larger rocks wreak?

By Mary Beth Griggs

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