An asteroid that exploded over Siberia a century ago, leaving 800 square miles of scorched or blown down trees, wasn't nearly as large as previously thought. Simulations conducted by Sandia National Laboratories the asteroid that destroyed the forest at Tunguska in Siberia in June 1908 had a blast force equivalent to one-quarter to one-third of the 10- to 20-megaton range scientists previously estimated. At this point it is still not possible to determine whether a 10 megaton asteroid would be more damaging than a Hurricane Katrina but scientists are concerned that even small asteroids could have a major impact on Earth.
Last Tuesday an asteroid at least 800 feet long was making a rare close pass by Earth, but scientists said there was no chance of an impact. The closest approach of 2007 TU24 will be 334,000 miles -- about 1.4 times the distance of Earth to the moon. An actual collision of a similar-sized object with Earth occurs on average every 37,000 years, according to scientists.