Tunguska

Tunguska is a remote region in Siberia?, Russia. It is mostly known for an enormous explosion in the early morning of June 30, 1908, which felled an estimated 60 million trees over 2,150 square kilometres. The size of the blast was estimated to be between 10 and 15 megatons? of TNT.

Due to the remoteness of the region, the first expedition to the site only arrived in 1938, led by Soviet geologist L. A. Kulik. It found no crater, despite the large amount of devastation.

In the absence of an obvious explanation, numerous fanciful theories have been offered, such as a small black hole, a piece of antimatter, and even UFO activity.

In scientific circles, the favored explanation for the blast is the impact of a meteorite. A related suggestion is that a meteorite exploded just above the Earth's surface. Whether the object was of cometary or asteroidal origin is still a matter of controversy.

In 2001, Farinella, Foschini, et. al released a study based on eyewitness accounts, seismic records, and samples from a 1999 expedition to the area. Their data suggests that the object originated from the [asteroid belt]?. However, it is still not understood how a stony object can totally disintegrate in the atmosphere.

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References:

Farinella P., Foschini L., et al Probable asteroidal origin of the Tunguska Cosmic Body, Astronomy and Astrophysics 377, 1081-1097 (2001) : http://www.edpsciences.fr/articles/aa/abs/2001/39/aah2886/aah2886.html

http://www-th.bo.infn.it/tunguska/