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The infamous Tunguska explosion , which mysteriously leveled an area of Siberian forest nearly the size of Tokyo a century ago, might have been caused by an impacting asteroid far smaller than previously thought. The fact that a relatively small asteroid could still cause such a massive explosion suggests "we should be making more efforts at detecting the smaller ones than we have till now," said researcher Mark Boslough, a physicist at Sandia National Laboratory in Albuquerque, N.M. The explosion near the Podkamennaya Tunguska River on June 30, 1908, flattened some 500,000 acres (2,000 square kilometers) of Siberian forest. Scientists calculated the Tunguska explosion could have been roughly as strong as 10 to 20 megatons of TNT — 1,000 times more powerful than the atom bomb dropped on Hiroshima . Wild theories have been bandied about for a century regarding what caused the Tunguska explosion, including a UFO crash , antimatter, a black hole and famed inventor Nikola Tesla's "death ray." In the last decade, researchers have conjectured the event was triggered by an asteroid exploding in Earth's atmosphere that was roughly 100 feet wide (30 meters) and 560,000 metric tons in mass — more than 10 times that of the Titanic. The space rock is thought to have blown up above the surface, only fragments possibly striking the ground. Now new supercomputer simulations suggest "the asteroid that caused the extensive damage was much smaller than we had thought," Boslough said. Specifically, he and his colleagues say it would have been a factor of three or four smaller in mass and perhaps 65 feet (20 meters) in diameter. (Source : Live Science ) 
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