In June 1908 an enormous fireball approached planet Earth, exploding with the force of an H-bomb just before it could impact the ground somewhere in Siberia. Air waves and ground shock were detected as far away as Western Europe, and nearly 1,000 square miles of Russian forest were devastated. The mass of the projectile was an estimated 100,000 tons, leading some space scientists to believe that it was a small comet rather than a meteorite. No fragments of the extraterrestrial