Tunguska Meteorite

the name given to a unique natural event that took place on June 30,1908, at 7:00 A.M. local time, in the basin of the Podkamennaia Tunguska River, in what is now the Evenki Autonomous Okrug (formerly Evenki National Okrug), Krasnoiarsk Krai, RSFSR. The event resembled the phenomena that accompany meteorite falls, but was distinguished by its enormous scale.

For several seconds a brilliant bolide (seeMETEOR) was observed traveling across the sky from southeast to northwest. A thick dust trail, which persisted for several hours, remained along the path of the bolide, which was visible over a vast territory in Eastern Siberia (within a radius of up to 800 km). After the luminous display, an explosion was heard over a distance of more than 1,000 km. In many settlements the ground and buildings shook as if in an earthquake, windowpanes cracked, dishes and utensils fell from shelves, and hanging objects swayed. Many people and various domestic animals were knocked down by the air wave. Seismographs in Irkutsk and a number of places in Western Europe recorded a seismic wave. The blast wave was recorded on barograms at numerous Siberian meteorological stations, in St. Petersburg, and at a number of meteorological stations in Great Britain.

The epicenter of the phenomena described above was first investigated in 1927 by L. A. Kulik. He discovered that trees had been blown down radially within a radius of up to 15–30 km from the epicenter; later expeditions noticed traces of a distinctive burn on trees that had remained intact. Round depressions filled with water, which Kulik mistakenly assumed to be meteorite craters, were found in the central part of the area. It was subsequently established that the holes were natural formations associated with permafrost, and it was also determined that approximately 10²³ to 10²⁴ ergs of energy was released during the explosion. From 1928 to 1930 two more expeditions were carried out by the Academy of Sciences of the USSR under Kulik’s leadership, and in 1938–39 an aerial photographic survey was made of the central area of the downed forest.

Study of the region of the epicenter was resumed in 1958, and the Committee on Meteorites of the Academy of Sciences of the USSR conducted three expeditions led by the Soviet scientist K. P. Florenskii. At the same time, research was begun by amateur enthusiasts associated with the Integrated Amateur Expedition. Later, the expedition was transformed into the Commission on Meteorites and Cosmic Dust of the Siberian Division of the Academy of Sciences of the USSR. The commission continues to conduct research (1976).

The phenomena observed are most fully explained by the comet hypothesis, according to which they were caused by the entry into the earth’s atmosphere of a small comet traveling at cosmic speeds. According to contemporary theory, comets consist of ice and various frozen gases with nickel-iron admixtures and inclusions of stony matter.

In 1975, G. I. Petrov determined that the Tunguska body was extremely friable and that its density was no more than ten times greater than the density of air at the earth’s surface. It was a “loosely packed snowball with a radius of 300 m and a density of less than 0.01 g/cm³.” At an altitude of approximately 10 km the entire body was vaporized, and the gas was dispersed in the atmosphere, thus explaining the unusually bright nights in Europe and Western Siberia after the event. The shock wave incident on the earth caused the collapse of trees.

Study of the Tunguska event is continuing.