The Tunguska event is a mysterious aerial explosion that occurred near the Tunguska River in Siberia. It took place at about a quarter after seven on the morning of June 30, 1908. The blast felled an estimated 60 million trees over 2,150 square kilometres. Witnesses observed a huge fireball, almost as bright as the Sun, plunging across the Siberian sky, terminating in a huge explosion that registered on seismic stations all across Eurasia. The size of the blast was later estimated to be between 10 and 15 megatons.
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Surprisingly, there was little scientific curiosity about the impact at the time, and due to the subsequent occurrence of war, revolution, and civil war in Russia, it wasn't until the 1920s that anyone performed a serious investigation of what had happened in Siberia in 1908.
In 1921, the Russian mineralogist Leonid Kulik visited the Podkamennaya Tunguska River basin as part of a survey for the Soviet Academy of Sciences. Locals told him of the great blast, of huge stretches of forest being flattened, of people being blown over by the shock.
The reports were basically consistent with each other, and Kulik was able to persuade the Soviet government to fund an expedition to the Tunguska region. His group reached the "ground zero" of the "event" in 1927. Much to their surprise, there was no crater, just a great region of scorched trees about 50 kilometers across. The trees pointed away from the center of the event, with a few still bizarrely standing upright at ground zero, their branches and bark stripped off.
Over the next ten years, there were three more expeditions to the area, and none of them discovered anything much different from what Kulik and his people had found. Kulik found a little "pothole" bog that he thought might be the crater, but after a laborious exercise in draining the bog, he found there were old stumps on the bottom, ruling out the possibility that it was a crater.
Kulik did manage to arrange an aerial photographic survey of the area in 1938, a few years before his death as a Red Army officer in the Great Patriotic War (Second World War). The aerial survey revealed that the event had knocked over trees in a huge butterfly-shaped pattern that provided information on the direction of the object's motion. It found no crater, despite the large amount of devastation.
Soviet experiments performed in the mid-1960s with model forests and small explosive charges slid downward on wires that duplicated this pattern suggested that the 1908 object had approached at an angle of roughly 30 degrees from the ground and 115 degrees from north, and exploded in mid-air.
Expeditions sent to the area in the 1950s and 1960s did find microscopic glass spheres in siftings of the soil. Chemical analysis showed that the spheres contained high proportions of nickel and iridium, which are found in high concentrations in meteorites, and indicated that they were of extraterrestrial origin. However, even this clue could not pin down the nature of the object precisely.
The precise cause of the Tunguska event remains unknown. In scientific circles, the leading 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 meteorite was of cometary or asteroidal origin is still a matter of controversy. Whatever the original cause of the event is, much of the data supports that the cause resembled a nuclear explosion.
In the absence of an obvious explanation, numerous alternative theories have been offered, such as a small black hole passing through the Earth, an impact from a piece of antimatter, and even the catastrophic destruction of a nuclear-powered alien spacecraft. However, there has not been much evidence for these exotic ideas, and simpler theories are available.
In 1930, the British astronomer F.J.W. Whipple suggested that the Tunguska event was produced by the impact of a small comet. A cometary meteorite, being composed primarily of ices and dust, could have completely vaporized by the impact with the Earth's atmosphere, leaving no obvious traces. The idea of a comet impact was supported by the "skyglows" observed across Europe for several evenings after the impact, apparently caused by dust that had been dispersed across the upper atmosphere. In addition, chemical analyses of the area have showed it to be enriched in cometary material.
The comet idea remained popular for over 50 years, with some astronomers speculating that it might have been a piece of the short-period Comet Encke. Materials from Encke appear to make up the stream of sky junk that create the Beta Perseid meteor shower, and the Tunguska event coincided with a peak in that shower.
In 1983, an astronomer named Zdenek Sekanina, working the NASA Jet Propulsion Laboratory, published a paper that undermined the comet theory. Sekanina pointed out that eyewitness accounts and other evidence point only to one explosion, and that the object passed through the atmosphere at a shallow angle, remaining intact to an altitude of 8.5 kilometers. A body composed of ice and gases could not have travelled such a distance without disintegrating. Proponents of the comet theory have suggested, in reply, that the object might have been an extinct comet with a stony mantle that allowed it to penetrate the atmosphere.
An alternative explanation is that the Tunguska meteorite was a stony asteroid. In 2001, Farinella, Foschini, et. al released a study suggesting that the object had arrived from the direction of the asteroid belt, working from eyewitness accounts, seismic records, and samples from a 1999 expedition to the area.
The chief difficulty in the asteroid theory is that a stony object should have produced a large crater where it struck the ground, but no such crater has been found. It has been hypothesized that the passage of the asteroid through the atmosphere caused pressures and temperatures to build up to a point where the asteroid abruptly disintegrated in a huge explosion. The destruction would have had to be so complete that no remnants of substantial size survived, and the material scattered into the upper atmosphere during the explosion would have caused the skyglows. However, it remains an open question why the meteorite should have disintegrated so abruptly.
The Tunguska Event does appear to be similar to magnetic storms that occur after thermonuclear explosions (such as from a nuclear weapon) in the stratosphere. Anomalous concentrations of electrical energy in the region could have produced an explosive releases of energy. Electromagnetic fireballs, spherical plasmoidss, and ball lightning have been reported to exhibit the same phenonomena. Other plasma and geomagnetic theories have been formed. V. K. Zhuravlev and A. N. Dmitriev, in 1984, proposes a "heliophysical" model that explains the Tunguska event as a result of plasmoids ejected from the Sun. Valeriy Buerakov also develops an independent model of an electromagnetic "ball" that could deliver such force.
Some have suggested that the Tunguska explosion may have been the result of an experiment by Nikola Tesla at Wardenclyffe from a 1908 article in Wireless Telegraphy and Telephone. In the article, Tesla states that he would be able to direct electrical energy to any point on the globe. The mechanism and inner workings behind Tesla's Wardenclyffe facility is not well understood. Tesla had stated it was an evolution of his magnifying transformer and could concentrate electromagnetic energy output over long distances. Tesla, in March 1907, did state that he was capable of "projecting wave energy" and, in April 1908, Tesla expounds on the possiblities of "direct application of electrical waves without the use of aerial engines or other implements of destruction".
It is not certain if Tesla ever used the Wardenclyffe facility for this manner. Reports of 1908 have Tesla testing the facility during Robert Peary's second North Pole expidition. Reportedly, Tesla operated the Wardenclyffe facility to send enormous power to an area west of the Peary expedition. Tesla's associate, George Scherff, witnessed these evernts at Wardenclyffe Tower. During the test, Wardenclyffe tower emitted a faint soft glow and killed an animal. Analysis of Peary's position and Tunguska deviates by 2 degrees on a straight line from the Wardenclyffe facility. Shortly afterward, Tesla stopped speaking of this type of possibility for Wardenclyffe-type installations (though he does introduce the concept of teleforce).
History
Early expeditions
Later expeditions
Theories
Comet impact
Asteroid impact
Electromagnetic effect
See also
External Links and References