The bizarre explosion in the skies over in Russia on Feb. 15, 2013 left scientists dumfounded. The asteroid 2012 DA14 was expected
to pass some 17K miles over Indonesia, but the Russian impactor wasn't foreseen: it flew from the direction of the sun where telescopes couldn't see it, and surprised everyone hours before the more-publicized asteroid's flyby.
A NASA news item today explains how scientists are piecing together what happened, using infrasound sensors operated by the Comprehensive Test Ban Treaty Organization (CTBTO).
Their purpose is to monitor nuclear explosions. Infrasound is a type of very low-frequency sound wave that only elephants and a few other animals can hear. It turns out that meteors entering Earth's atmosphere cause ripples of infrasound to spread through the air of our planet. By analyzing infrasound records, it is possible to learn how long a meteor was in the air, which direction it traveled, and how much energy it unleashed. The Russian meteor's infrasound signal was was the strongest ever detected by the CTBTO network. The furthest station to record the sub-audible sound was 15,000km away in Antarctica.
Video above: Listen to the infrasound recording, sped up 135x into the range of human hearing. The video comes from the Comprehensive Test Ban Treaty Organization's YouTube channel.
Peter Brown, University of Western Ontario Professor of Physics, analyzed the data and determined that the asteroid was about 17 meters in diameter and weighed approximately 10,000 metric tons.
"It struck Earth's atmosphere at 40,000 mph and broke apart about 12 to 15 miles above Earth's surface. The energy of the resulting explosion exceeded 470 kilotons of TNT." For comparison, the first atomic bombs produced only 15 to 20 kilotons.
Based on the trajectory of the fireball, analysts have also plotted its orbit. "It came from the asteroid belt, about 2.5 times farther from the sun than Earth."
More: What Exploded over Russia? [NASA Science].
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