http://www.businessinsider.com/asteroid-flyby-nearer-than-moon-2017-1 "The asteroid, dubbed 2017 AG13, was discovered only Saturday by the University of Arizona's Catalina Sky Survey, according to an email from Slooh, a company that broadcasts live views of space. It's between 50 and 111 feet (15 to 34 meters) long, and when it swung by Earth, 2017 AG3 was moving at 9.9 miles per second (16 kilometers per second). The near-Earth object, or NEO, came within about half the distance that the moon is from Earth, according to Slooh. .... Had a porous rock asteroid of 111 feet (34 meters) long hit Earth at a 45-degree angle, the simulator found, it would have exploded as an air burst. The blast would have released about 700 kilotons' worth of energy — dozens of times more powerful than the atomic bomb detonated over Hiroshima." BTW, the Hiroshima bomb had a yield of 12-18 KT...
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