February 15, 2013
NASA scientists say the surprise Feb. 15 atmospheric entry of a large meteorite measuring 15 meters in diameter over Russia, coincident with the close passage of asteroid 2012 DA14, is a major reminder that detection of near-Earth objects (NEOs) remains a key issue for governments worldwide.
“It’s an international problem, certainly in terms of discovery,” says Paul Chodas, research scientist in the NEO Program Office at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “If an asteroid should hit, it could hit anywhere on Earth.” Beyond the challenges involved in deflecting an asteroid, Chodas adds that major questions facing the international community include political issues, particularly if deflections threaten some parts of Earth over others.
NASA says the Russia meteor is not related to asteroid 2012 DA14 that passed by Earth within hours of the event at a distance of more than 17,000 mi. (27,360 km). “Early assessments of the Russia meteor indicate it was about one-third the size of 2012 DA14 and traveling in a different direction,” says the agency. The meteorite exploded at an estimated altitude of 20 to 25 km (12 to 15 miles) over Russia’s Ural mountains in the Chelyabinsk region.
Weighing around seven metric tons, the meteorite was traveling at 18 km/sec (40,000 mph) when it hit the atmosphere at a shallow angle of less than 20 degrees. Videos show the object burned brightly, and lasted just over 30 seconds, creating a smoke trail more than 300 mi. long, before breaking apart in a violent explosion. NASA estimates the energy released was equal to between 300 and 500 kilotons of explosive, or the same as a nuclear blast.
The “shock wave propagated down through atmosphere, causing large numbers of windows to break, walls to collapse and minor damage to the city,” says Bill Cooke, lead for the Meteoroid Environments Office at NASA’s Marshall Space Flight Center in Huntsville, Ala. The damage, which also caused injuries to more than 950 people, was “due to the effect of the shock wave — not due to fragments striking the ground.”
Preliminary analysis indicates the object originated in the asteroid belt. “It does appear to be an asteroid in nature,” says Cooke who adds the object was small enough to be classified as a large meteorite. “It was not detected because it came out of the daylight sky and was not detected by any Earth-based telescopes.
“The fact it broke up suggests it was probably not an iron nickel asteroid like the one that hit in 1947 over the Soviet Union,” he says. NASA meanwhile expects to reveal first images of the DA14 asteroid over the next few days.