* Astronomy

The leading scientific explanation for the explosion is the air burst of an asteroid 6-10 kilometres above Earth's surface. Meteoroids enter Earth's atmosphere from outer space every day, travelling at a speed of at least 11 kilometres per second. The heat generated by compression of air in front of the body (ram pressure) as it travels through the atmosphere is immense and most asteroids burn up or explode before they reach the ground. Since the second half of the 20th century, close monitoring of Earth's atmosphere has led to the discovery that such asteroid air bursts occur rather frequently. A stony asteroid of about 10 metres in diameter can produce an explosion of around 20 kilotons, similar to that of the Fat Man bomb dropped on Nagasaki, and data released by the U.S. Air Force's Defence Support Program indicate that such explosions occur high in the upper atmosphere more than once a year. Tunguska-like megaton-range events are much rarer. Eugene Shoemaker estimated that such events occur about once every 300 years.
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Scientist Dismisses Tunguska Meteorite Fragment Find Claims

Natalya Artemyeva of the Russian Academy of Sciences Geosphere Dynamics Institute said she was surprised that Zlobin had not conducted geochemical analysis of the fragments.
The samples, which are still pending chemical analysis, were mothballed until 2008, Zlobin said, without elaborating on the reasons. Russian academia suffered a dramatic decline after the Soviet Unions demise in 1991 due to lack of funding.
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Title: Discovery of probably Tunguska meteorites at the bottom of Khushmo river's shoal
Authors: Andrei E. Zlobin

The author describes some stones which he found at the bottom of Khushmo River's shoal during 1988 expedition into the region of the Tunguska impact (1908). Photos of stones are presented. Three stones have traces of melting and the author consider these stones as probable Tunguska meteorites. Some arguments are presented to confirm author's opinion. Results of investigation of prospect holes in peat-bogs are briefly described too. New data concerning heat impulse of the Tunguska impact are obtained. There is the assumption that some meteorites which are formed during comet impact looks like stony or glass-like thin plates with traces of melting.

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Title: Magnetic and seismic reflection study of Lake Cheko, a possible impact crater for the 1908 Tunguska Event
Authors: L. Gasperini, L. Cocchi, C. Stanghellini, G. Stanghellini, F. Del Bianco, M. Serrazanetti, C. Carmisciano

A major explosion occurred on 30 June 1908 in the Tunguska region of Siberia, causing the destruction of over 2,000 km2 of taiga; pressure and seismic waves detected as far as 1,000 km away; bright luminescence in the night skies of Northern Europe and Central Asia; and other unusual phenomena. This "Tunguska Event" is probably related to the impact with the Earth of a cosmic body that exploded about 5-10 km above ground, releasing in the atmosphere 10-15 Mton of energy. Fragments of the impacting body have never been found, and its nature (comet or asteroid) is still a matter of debate. We report here results from a magnetic and seismic reflection study of a small (~500 m diameter) lake, Lake Cheko, located about 8 km NW of the inferred explosion epicenter, that was proposed to be an impact crater left by a fragment of the Tunguska Cosmic Body. Seismic reflection and magnetic data revealed a P wave velocity/magnetic anomaly close to the lake center, about 10 m below the lake floor; this anomaly is compatible with the presence of a buried stony object and supports the impact crater origin for Lake Cheko.

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