A new explanation for a massive blast over a remote Siberian forest in 1908 is even stranger than the mysterious incident itself. Known as the Tunguska event, the blast flattened more than 80 million trees in seconds, over an area spanning nearly 2,000 square kilometers — but left no crater. A meteor that exploded before hitting the ground was thought by many to be the culprit. However, a comet or asteroid would likely have left behind rocky fragments after blowing up, and no "smoking gun" remnants of a cosmic visitor have ever been found. Now, a team of researchers has proposed a solution to this long-standing puzzle: A large iron meteor hurtled toward Earth and came just close enough to generate a tremendous shock wave. But the meteor then curved away from our planet without breaking up, its mass and momentum carrying it onward in its journey through space.