Using sensors designed to detect rogue nuclear tests, scientists have learned more about the meteor that exploded over Russia. It was much bigger than they first thought.
Initially, the Russian Academy of Science estimated the object's mass at about 10 metric tons (11 US tons). With more data in hand, researchers now say the object had a mass of 7,000 metric tons (7,700 US tons) and a diameter of about 50 feet.
The blast released energy comparable to a 300- to 500-kiloton nuclear warhead, says Bill Cooke, who heads the meteoroid environment office at NASA's Marshall Space Flight Center in Hunstville, Ala. By Comparison, the Nagasaki nuclear bomb had a yield of 20 to 22 kilotons.
The asteroid's breakup at an altitude some 12 to 15 miles above Russia's Chelyabinsk region represents the largest recorded asteroid encounter since 1908, when another asteroid or comet exploded over the Tunguska River in Siberia, leveling some 820 square miles of forest, says Paul Chodas, a scientist with the near-Earth object program at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.