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  • What Exploded over Russia? - presented by Science@NASA

  • When the sun rose over Russia's Ural Mountains on Friday, Feb. 15th,

  • many residents of nearby Chelyabinsk already knew that a space rock was coming.

  • Later that day, an asteroid named 2012 DA14 would pass by

  • Earth only 17,200 miles above Indonesia.

  • There was no danger of a collision, NASA assured the public.

  • Maybe that's why, when the morning sky lit up with a second sun

  • and a shock wave shattered windows in hundreds of buildings around Chelyabinsk,

  • only a few people picking themselves off the ground figured it out right away.

  • This was not a crashing plane or a rocket attack.

  • "It was a meteor strike--the most powerful since the Tunguska event of 1908,"

  • says Bill Cooke of NASA's Meteoroid Environment Office.

  • In a one in a million coincidence that still has NASA experts shaking their heads,

  • a small asteroid completely unrelated to 2012 DA14

  • struck Earth only hours before the publicized event.

  • "These are rare events and it is incredible to see them happening on the same day,"

  • says Paul Chodas of NASA's near-Earth Object Program at JPL.

  • Researchers have since pieced together what happened.

  • The most telling information came from a network of infrasound sensors

  • operated by the Comprehensive Test Ban Treaty Organization.

  • Their purpose is to monitor nuclear explosions.

  • Infrasound is a type of very low-frequency sound wave that only

  • elephants, homing pigeons 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's meteor infrasound signal was detected by multiple stations,

  • including one in Alaska more than 6500 km from Chelyabinsk.

  • Western Ontario Professor of Physics Peter Brown analyzed the data:

  • "The asteroid was about 17 meters in diameter

  • and weighed approximately 10,000 metric tons," he reports.

  • "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 originally came from the asteroid belt,

  • about 2.5 times farther from the sun than Earth," says Cooke.

  • Comparing the orbit of the Russian meteor to that of 2012 DA14,

  • NASA orbit analysts have shown that there is no connection between the two.

  • "These are independent objects," Cooke says.

  • "The fact that they reached Earth on the same day,

  • one just a little closer than the other, appears to be a complete coincidence."

  • Infrasound records confirm that the meteor entered the atmosphere

  • at a shallow angle of about 20 degrees and lasted more than 30 seconds before it exploded.

  • The loud report, which was heard and felt for hundreds of miles,

  • marked the beginning of a scientific scavenger hunt.

  • Thousands of fragments of the meteor are now scattered across the Ural countryside,

  • and a small fraction have already been found.

  • Preliminary reports, mainly communicated through the media,

  • suggest that the asteroid was made mostly of stone with a bit of iron

  • "in other words, a typical asteroid from beyond the orbit of Mars," says Cooke.

  • "There are millions more just like it."

  • And that is something to think about as the cleanup in Chelyabinsk continues.

  • For more news about things coming out of the blue, visit science.nasa.gov

What Exploded over Russia? - presented by Science@NASA

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