This event was a large explosion caused by the impact of a small asteroid or comet, which occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia on June 1908. The explosion occurred at an altitude of 5–10 kilometres (3–6 mi) at 60.886°N, 101.894°E. Different studies have yielded widely varying estimates of the impacting object’s size, on the order of 60 m (200 ft) to 190 m (620 ft). It is the largest impact event on or near Earth in recorded history. It is classified as an impact even though the asteroid or comet is believed to have burst in the air rather than hitting the surface.
What happened? Of course there was much curiosity as much as lay scientists. But the first expedition to examine the region left more than a decade later, in 1921. On occasion, the Soviet geologist Leonid Kulik failed to achieve the exact location, and deduced that the event was due to fall of a large meteorite. This hypothesis eventually persuaded the Soviet government to fund another expedition in 1927, attracted by the possibility of finding a meteorite iron of commercial value. But no crater was found, much less a meteorite. Other expeditions have confirmed this lack. It was calculated that the magnitude of the blast was between 10 and 15 million tons of dynamite. But the object that caused it has not touched the ground, smashing into the air, about 8 km high. Until now the most intense event similar happened in 1930 on the river Corucia, Amazonas, reaching a maximum energy of one million tons of dynamite. Rejected the assumption of a meteorite, but taking into account the reports of the fireball, a hypothesis emerged even more spectacular – and most likely: in 1908, a piece of comet collided with Earth.
There were many theories about what cause it…from acceptable meteor, Russian missile, fireball to UFO. But these otherworldly conspiracy theories do nothing to advance the serious investigation of the Tunguska Event, they are creative and mildly amusing.
Read more: http://en.wikipedia.org/wiki/Tunguska_event