NASA says ‘small asteroid’ exploded over Russia: event took everyone by surprise

February 16, 2013 – RUSSIA – At a news conference Friday, NASA scientists said the object that exploded over Russia was a “tiny asteroid” that measured roughly 45 feet across, weighed about 7,000 tons and traveled about 40,000 mph. The object vaporized roughly 15 miles above the surface of the Earth, causing a shock wave that triggered the global network of listening devices that was established to detect nuclear test explosions. The force of the explosion measured between 300 and 500 kilotons, equivalent to a modern nuclear bomb, according to Bill Cooke, head of the Meteoroid Environment Office at NASA’s Marshall Space Flight Center in Huntsville, Ala. “When you hear about injuries, those are undoubtedly due to the events of the shock striking the city and causing walls to collapse and glass to fly, not due to fragments striking the ground,” Cooke said. Scientists believe the object originated from the asteroid belt, a vast collection of debris orbiting between Mars and Jupiter that consists of leftover bits from the formation of the solar system. The asteroid probably traveled for a year before it burst into the atmosphere Friday. As yet, no fragments have been recovered, but experts believe the asteroid was rocky in nature, and not formed of dense iron and nickel. The fact that the asteroid hit on the same day that the world was anticipating the close flyby of a larger asteroid, 2012 DA14, was an extraordinary coincidence. The smaller asteroid was traveling in a very different trajectory and much more quickly than DA14, indicating they were not related, according to Paul Chodas, research scientist in the Near-Earth Object Program office at NASA’s Jet Propulsion Laboratory in La Cañada Flintridge. “I would call this a tiny asteroid,” Chodas said. “This is the largest recorded event since the Tunguska explosion in 1908.” That event, which may have involved a meteor, leveled more than 800 square miles of forest in Russia. Asteroids are tracked by telescope, as they are too far away to be detected by radar. Because of this, they are observable only when illuminated by the sun against a dark background. If they are small and dark-colored, they are far more difficult to observe. In the case of the Russian asteroid, it approached Earth with the sun behind it. “The reason it wasn’t detected by telescopes on Earth is because it literally came out of the daylight sky and, as you know, telescopes can’t see things in the daytime,” Cooke said. Scientists estimate that anywhere between 80 and 200 tons of space-borne debris hits Earth’s atmosphere every day. Most of those objects are the size of a grain of sand. Objects that contact the Earth’s surface are much rarer. NASA leads international efforts to track much larger, asteroid-size objects, and Chodas said the agency had identified 95% of them. It’s the smaller ones that pose a problem. “They are very difficult to find,” he said. –LA Times

No meteor fragments found in lake: Russian authorities say divers have explored an icy lake in search of fragments of the huge meteor that exploded above the Ural Mountains, but found nothing. People in Russia’s Chelyabinsk region panicked as the 10-ton meteor lit up the morning sky Friday and exploded with the force of at least 20 nuclear bombs. The explosion unleashed a shock wave that blew out thousands of windows, damaged buildings and left more than 1,100 people injured. The Interior Ministry said most of the injuries were caused by flying glass. The regional governor said the damage is estimated at $33 million. The planetary science director at the U.S. space agency, NASA, says the event was an “exception.” Jim Green said Friday that “fireballs” of some kind happen on a daily basis, but most of them are not seen because they fall over the ocean or in remote areas. The Russian Academy of Sciences says the meteor entered Earth’s atmosphere at a speed of at least 54,000 kilometers per hour. Its entry occurred just hours before an asteroid known as 2012 DA14 passed between Earth and some orbiting satellites. NASA said the 45-meter-wide asteroid came as close as 27,000 kilometers above Earth. –VOA

contribution Maria