[Black Blade]

Some think that the Tunguska Blast of 1909 was a comet that vaporized and exploded over western Siberia, others think it was a meteor. The explosion is believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 5–10 kilometers (3–6 mi) above the Earth's surface. Different studies have yielded varying estimates of the object's size, with general agreement that it was a few tens of meters across.

Although the meteoroid or comet burst in the air rather than hitting the surface, this event is still referred to as an impact. Estimates of the energy of the blast range from 5 to as high as 30 megatons of TNT (21–130 PJ), with 10–15 megatons of TNT (42–63 PJ) the most likely—roughly equal to the United States' Castle Bravo thermonuclear bomb tested on March 1, 1954, about 1,000 times more powerful than the atomic bomb dropped on Hiroshima, Japan, and about one-third the power of the Tsar Bomba, the largest nuclear weapon ever detonated. The explosion knocked over an estimated 80 million trees covering 2,150 square kilometres (830 sq mi). It is estimated that the shock wave from the blast would have measured 5.0 on the Richter scale. An explosion of this magnitude is capable of destroying a large metropolitan area.

The composition of the Tunguska body remains a matter of dispute. In 1930, the British astronomer F.J.W. Whipple suggested that the Tunguska body was a small comet. A cometary meteorite, being composed primarily of ice and dust, could have been completely vaporized by the impact with the Earth's atmosphere, leaving no obvious traces. The comet hypothesis was further supported by the glowing skies (or "skyglows" or "bright nights") observed across Europe for several evenings after the impact, possibly explained by dust and ice that had been dispersed from the comet's tail across the upper atmosphere. The cometary hypothesis gained a general acceptance amongst Soviet Tunguska investigators by the 1960s.