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Photograph from the Soviet Academy of Science 1927 expedition led by Leonid Kulik.
The Tunguska "Impact"?

In the early morning hours of June 30 1908, in Central Siberia, a strange explosion took place that flattened 2,150 kilometers of forest and left 80 million trees lying down in a radial pattern. Seismic instruments in the area measured the ground motion to be equivalant to a magnitude 5 earthquake. The air wave disturbance was detected by barometers in England as it circled the globe twice. Sunlight, reflected off the spreading debris, lit up the night sky in Europe and Western Asia for several days. Witnesses told of a fireball that streaked across the sky and detonated in the air. Effects of the explosion were felt by witnesses in a nearby trading post, some 70 kilometers away, who were knocked off their feet and seared from the heat. It would take two decades before a research expedition would be sent to the blast zone, but the damage observed by scientists when they arrived was that of an exterrestial object colliding with earth, but there was only one problem, there was no crater to show that an impact occured. The damage observed indicates that the explosion took place about 6 to 8 kilometers above ground and released energy equivalant to 15 megatons of TNT, about a thousand times more powerful then the bomb dropped on Hiroshima. Some refer to this event as the "Tunguska Blast" that is named for a river that runs through the area.

Theories

Many scientists today are still trying to figure out what could have caused such a phenomenon. Some theorists believe that an impact did occur; that a nearby lake was the missing crater that scientists have been searching for. Within this theory of impact there have risen two sub-theories and scientists are questioning if this impact was brought about by either asteroid or comet. The theory behind these two impacts is clear in how the scientists collect and research the surrounding areas. If some sort of terrestrial object were to fall from space such as an asteroid or meteorites there would be other evidence that suggests several other smaller impacts from the the trailing pieces. The second portion of this theory suggests that if this impact were driven by comet then scientists would be able to find extraterrestrial chemical compounds within the soil. One of the biggest claims that support this theory was that the lake followed the trajectory of the fireball witnesses had seen. But scientists have claimed that if the lake was actually the crater, sediment from the depth of the impact would have been found around the lake, and no such evidence can be found. Also the dating of the surrounding trees also contradict this theory because of their age. Another theory produced was that a small black hole passed through the earth, but this has been somwhat disproven because there has been no exit phenomenon that would definately have occured if it passed through the earth. One other theory suggested is that this was a sudden explosion of natural gases exploding from the earth. Even UFO conspiracy theorists have claimed Tunguska to be the sight of an alien spaceship crash. Theories like these have been surrounding this occurence since it happened in 1908. Some locals believed the blast was a visitation by the god Ogdy, who had cursed the area by smashing trees and killing animals.

Todays Research

Several research expeditions have been sent to "ground zero" where the impact of the explosion took place. The first team didn't arrive until 1927, 19 years after the intial explosion, this was their second and successful attempt after an initial attempt in 1921. This team was led by scientist Leonid Kulik. Kulik, after interviewing eye witnesses to the explosion, concluded that what took place was that a meteor or asteroid fell to Earth but exploded in mid-air. Most scientists today believe this is what happened. A reasearch team in 1961, went out to investigate the site and found two very interesting things. The first thing they found was that the trees damaged in the area showed signs of damage on the uppermost branches which suggest that the fire or ignition that started the fire come from up above, unlike most fires that start at the ground up. Also the damage done to the tree's diminishes the further away from the epicenter they are. The scientist believed they found the epicenter because all trees leading to it were on there sides while the trees were the epicenter actually accured were still standing erect. Another thing they found was meteoritic fragments (or dust) in the area that suggest with a "high probablity" that the debris was from a meteorite. Further tests were needed. A theory proposed by NASA suggests that a meteor entered Earth's atmosphere traveling at a speed of about 33,500 mph. A 220 million pound space rock would heat the surrounding area to about 44,500 degrees Faherenheit. At approximately 28,000 feet, the combination of heat and pressure would have caused the asteroid to explode, extinguising itself releasing energy equivalent to about 185 Hiroshima bombs. Kulik had visited the site on 3 seperate occasions finally getting an account from a man that was thrown from his seat from the blast, the man who was at the Vanara trading post said... "Suddenly in the north sky… the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire… At that moment there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing. The earth trembled." Another research team during the months of July-August in the year 1991 began to try and strengthen the ideas that in fact it was a impact from space. Italian researchers found several microspherules in the trees of Tunguska. These microspherules are also referred to as micro particles. After much analysis these researches found that these chemical elements will strengthen the asteroidal hypothesis.



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Map of Tunguska Events Location

Sources http://www-th.bo.infn.it/tunguska/index.html

http://www.jpl.nasa.gov/news/features.cfm?feature=1769
http://abob.libs.uga.edu/bobk/tungmet.html
http://www.jstor.org/stable/20465508
http://www.jstor.org/stable/1689889
http://www.jstor.org/stable/1687233
http://science.nasa.gov/headlines/y2008/30jun_tunguska.htm
www.crystalinks.com/tunguskaevent.html
http://news.nationalgeographic.com/news/2007/11/071107-russia-crater_2.html