The meteor was a once-in-a-century event, NASA officials said, describing it as a "tiny asteroid."
The space agency revised its estimate of the meteor's size upward late Friday from 49 feet (15 meters) to 55 feet (
17 meters), and its estimated mass from 7,000 tons to
10,000 tons.
The space agency also increased the estimated amount of energy released in the meteor's explosion from about 300 to nearly
500 kilotons. By comparison, the nuclear bomb the United States dropped on Hiroshima in 1945 released an estimated 15 kilotons of energy.
The whole event, from the meteor's atmospheric entry to its disintegration in the air above central Russia, took 32.5 seconds, NASA said.
“This is the largest recorded event since the 1908 Tunguska event,” Dr. Chodas said. On June 30, 1908, the explosion of a meteor, believed to be an asteroid, flattened millions of trees over 800 square miles in a remote, largely unhabited area of central Siberia about 1,200 miles away from Friday’s event.
At a NASA news conference Friday afternoon, Bill Cooke, who leads the Meteoroid Environment Office at the Marshall Space Flight Center in Huntsville, Ala., said the orbital path of the meteor showed that it was an asteroid, not a comet.At its farthest point from the Sun, it was 2.5 times as far away as the Earth, before its elliptical path took it closer, and the Earth got in its way on Friday.
Other large meteors could have splashed unnoticed in an ocean in decades past, but nowadays military satellites on the watch for missile launches would certainly notice an incoming meteor this bright.
The asteroid was impossible to detect, Dr. Cooke said, because it was approaching from the dayside. “And as you know, telescopes can’t see things during the daytime,” he said.Clark R. Chapman, a senior scientist at the Southwest Research Institute’s Department of Space Studies based in Boulder, Colo., said this was the first time a crashing meteor is known to have injured a large number of people. “That’s basically never happened before,” he said.
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