* Astronomy

On the morning of June 30, 1908, the sky exploded over a remote region of central Siberia. A fireball as powerful as hundreds of Hiroshima atomic blasts scorched through the upper atmosphere, burning nearly 800 square miles of land. Scientists today think a small fragment of a comet or asteroid caused the "Tunguska event," so named for the Tunguska river nearby. Now, a controversial new scientific study suggests that a chunk of a comet caused the 5-10 megaton fireball, bouncing off the atmosphere and back into orbit around the sun. The scientists have even identified a candidate Tunguska object - now more than 100 million miles away - that will pass close to Earth again in 2045. Is there a hidden, but powerful, danger inside the seemingly harmless comet?

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Ed ~ The asteroid, 2005 NB56, has been removed from the Near Earth Object Impact Risk Table.