Jennifer Ouellette: New research on Tunguska finds such events happen less often than we thought: "Eyewitness: 'Suddenly the sky appeared like it was split in two, high above the forest.'... scientists deduced that the Chelyabinsk object was most likely a stony asteroid the size of a five-story building that broke apart 15 miles (24km) above the ground. The resulting shock wave was as powerful as a 550 kiloton nuclear explosion—and the Tunguska object was probably much larger. Based on the Chelyabinsk models—augmented with survey records from the Tunguska region shortly after the event—the scientists concluded the Tunguska object was probably stony (rather than icy), and measured between 164 and 262 feet in diameter (about 50 to 80 meters). It whipped through the atmosphere at 34,000 miles per hour (about 54,700km/h), and produced an amount of energy equivalent to the 1980 eruption of Mount Saint Helens. Those models, plus current data on the asteroid population, also enabled researchers to calculate how frequently such impact events are likely to occur. The good news is that this research suggests mid-size rocky bodies like the one that likely caused the damage at Tunguska occur less frequently than previously thought—on the order of millennia, rather than centuries...


#noted #2019-10-14

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