“I was sitting in the porch of the house at the trading station of Vadecara at breakfast time...when suddenly in the north...the sky was split in two and high above the forest the whole northern part of the sky appeared to be covered with fire. At that moment I felt great heat as if my shirt had caught fire; this heat came from the north side. I wanted to pull off my shirt and throw it away, but at that moment there was a bang in the sky, and a mighty crash was heard. I was thrown to the ground about three sajenes [about 7 meters] away from the porch and for a moment I lost consciousness.... The crash was followed by noise like stones falling from the sky, or guns firing. The earth trembled, and when I lay on the ground I covered my head because I was afraid that stones might hit it.” - S.B. Semedec, an eyewitness in the village of Vadecara.
No one knows for sure what caused the powerful explosion in the skies over the Tunguska river in Russia on June 30, 1908, but after a hundred and five years of scientific expeditions and studies, the public may finally be close to getting some answers.
Very early in the twentieth century, the Russian government would make no attempt to investigate in the immediate aftermath of an object exploding in the atmosphere above their country with an explosive force a thousand times that of the nuclear bomb dropped on Hiroshima in 1945 and leveling 80 million trees in the Russian wilderness. One can only imagine the response the government of the USSR would have had to such an event in the mid-twentieth century, and it can be said with confidence that the earth and its inhabitants seem very lucky that the Tunguska event did not occur 50 years later than it actually did.
As it happened however, Russia's government at the time was engaged in its own chaotic transformation, and in that time it was unthinkable that such an event could have been caused by anything but a natural occurrence. As such, Russia would not investigate or respond to the explosion until 12 years later, when in 1921 the government's newly created Academy of Sciences appointed mineralogist L.A. Kulik to travel to the region in search of evidence that a meteorite had caused the explosion above the earth and the mass destruction of the previously lush forests.
Kulik led 5 expeditions to the region between the years of 1921 and 1939, and aside from speculation derived from eyewitness accounts, he was unable to find any evidence to validate the theory that a meteorite had caused the explosion. It seemed there was neither impact crater nor field of strewn particles. Kulik could find no evidence of impacting iron, and no fragments of the supposed meteorite.
Soon after Kulik's fifth and final unsuccessful expedition, F.J.W. Whipple proposed that rather than a meteorite, a small comet could have been responsible for the atmospheric explosion and resultant terrestrial devastation in the Tunguska region in 1908. Even at the time that he presented it, Whipple lacked confidence in his comet hypothesis, and publicly stated this lack of confidence in the same article in which he introduced the theory. In the 1934 article, Whipple suggests the possibility that the event could have been caused by a comet colliding with the earth, and yet concedes to previous opinions that the event was probably caused by “an inactive, low-density, friable body.”
As study of the event continued and no conclusive evidence linking it to a meteorite impact surfaced, many alternative explanations were proposed.
As the immense power of atomic energy began to become known, comparisons were drawn and theories were proposed involving a nuclear explosion. Some took this theory further than others, and the speculation concerning an explanation for such an explosion ranged from the detonation of a man-made nuclear weapon to the claim of a humanitarian crash-landing of a nuclear powered extra-terrestrial spacecraft (humanitarian because of the remote location of the “crash” and little loss of human life) – and everywhere in between.
Still lacking a convincing explanation, some scientists suggested that the explosion could have been caused by the explosion of anti-matter entering the atmosphere, and others suggested that a very small black hole could have traveled through the earth's surface and exited on the other side of the world, through the Atlantic Ocean. However, these explanations lack credible evidence and do not account for many of the circumstances surrounding the event, such as reports of unusual lights in the skies across Asia and Europe in the nights following the event.
In the absence of meteorite fragments, the scientific community from the latter half of the 20th century until now seems to believe that the most supportable explanation for the Tunguska event is that of a cometary collision with the earth's atmosphere.
In the spring of 2013 Russian researcher Andrei Zlobin claimed to be in possession of the first known stone fragments which could be from the Tunguska event. Apparently these fragments were found in 1988 and were not even looked at closely until 2008, when Zlobin began to study them.
For unknown reasons at the time of this writing a chemical analysis of the fragments is still pending. If they prove to be from the Tunguska event, they could definitively rule out the most implausible of the proposed explanations, but they may still not definitively determine whether the event was caused by a meteorite or comet since comets have nuclei comprised of - among other things - rock and dust. Zlobin says an analysis of the density of the materials found is consistent with the estimated density of the nucleus of Hailey's comet, so even if the materials are linked to the cause of the Tunguska explosion, they may not solve the mystery entirely. Until the scientific community at large is furnished with more information, either from these fragments or elsewhere, the debate surrounding the cause of the Tunguska event will continue.