At roughly 7:17 a.m. Local time on June 30, 1908, a blinding column of blue-white light split the sky above the remote Podkamennaya Tunguska River in central Siberia, and then the forest simply ceased to exist. The Tunguska Event released energy estimated at 10, 15 megatons, roughly 1,000 times the force of the Hiroshima bomb, and flattened approximately 2,000 square kilometers of pine forest without leaving a crater. Witnesses eighty kilometers away were thrown from their feet; the pressure wave circled the globe twice. Because the region was nearly uninhabited, casualties were minimal, but the scale of destruction was planetary. Scientists believe a stony asteroid or comet fragment roughly 50, 80 meters wide disintegrated mid-air in a superbolide explosion before ever touching ground. The event remained scientifically obscure until Leonid Kulik led the first expedition to the site in 1927. Today it stands as humanity's most vivid proof that space rocks capable of erasing cities still cross Earth's path, a sobering fact that drives every planetary-defense program on the planet.