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Asteroid blast reveals holes in Earth's defences

点击量:   时间:2019-03-08 08:14:15

IT WAS one hell of an explosive wake-up call. On 8 October, an asteroid detonated 20 kilometres above South Sulawesi in Indonesia, releasing as much energy as a 50-kiloton nuclear bomb, according to an estimate released last week. It was one of the largest asteroid explosions ever observed, yet no one had seen it coming. That’s not surprising, says Tim Spahr, director of the Minor Planet Center in Cambridge, Massachusetts. Only a tiny fraction of asteroids less than 100 metres across have been catalogued,