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ASSOCIATED PRESS
FILE - In this Friday, Feb. 15, 2013 file photo provided by Chelyabinsk.ru, a meteorite contrail is seen over the Ural Mountains' city of Chelyabinsk, about 1500 kilometers (930 miles) east of Moscow, Russia. Scientists on Wednesday recovered what could be the largest part of this meteor from Chebarkul Lake outside the city. They weighed it using a giant steelyard balance, which displayed 570 kilograms (1,256 pounds) before it broke. (AP Photo/Chelyabinsk.ru, Yekaterina Pustynnikova)
Asteroid strikes similar in size to the explosion over Russia in February may be 10 times more likely than previously thought, according to a paper published in the journal Nature.
Using infrasonic detectors that can identify smaller bodies missed by telescopes, strikes from impactors between 10 and 50 meters in diameter may occur every 20 or even 10 years, compared with an earlier estimate of once a century, according to research led by Peter Brown at the University of Western Ontario in Canada.
The meteor that exploded in the skies above Russia’s Urals region was about 19 meters in diameter and emitted energy equivalent to about 500 kilotons of TNT, Brown said in the paper. Asteroids of that size are now detectable by measuring infrasound, which is at a low frequency that isn’t audible to humans and can be detected when they enter the earth’s atmosphere, said Jiri Borovicka, one of the co-authors.
"When they travel by supersonic speed, they produce these sonic waves during their flight," Borovicka said in a telephone interview. With telescopes, "we can only see smaller asteroids if they are relatively close to the Earth. It’s still a matter of luck to observe."
The burst in Russia sent shock waves that smashed windows and injured more than 725 people in the city of Chelyabinsk. The Tunguska event, in which a asteroid or comet caused the most powerful natural explosion in recent history, leveled 800 square miles of forest in Siberia in 1908, releasing energy of about 5 to 15 megatons.
