It was early in the morning on June 30, 1908. A bluish streak of light raced across the sky of Tunguska, a remote area of Russian Siberia, Tunguska. Shortly after, the few residents of the area heard a loud explosion.The ground shook and a blast wave knocked people off their feet. Effects were felt throughout Eurasia and as far away as London.

The first scientific investigation took place nearly two decades later. Events of the day, World War I and the Russian Revolution, and the remoteness of the site, combined to delay any search of the region.

The scientific party arrived to find a sight none had ever seen. The forest in the area was scorched, with many trees flattened and pointing out from the epicenter of some catastrophic event. There was no crater or any immediate sign of what had happened on that summer day in 1908.

The leading Soviet scientists of the era believed that an asteroid had struck the earth, causing the Tunguska event. The Soviet government sent several other expeditions to the area in the 1950's and the 1960's, looking for evidence of a meteor entering the atmosphere and exploding. Results were suggestive but no large pieces of such a body were found.

Western scientists have also researched the event since the end of the Soviet Union. An Italian expedition using ground penetrating radar and other modern tools investigated a lake, Lake Cheko, very near the center of the event damage. They discovered that the lake may, in face, be an impact crater. Its bottom is shaped very differently than most Siberian lakes. The sediments on the bottom are stratified into two layers, with the earliest deposits much more like debris than sediment from the small stream that enters the lake.

The sheer violence of the event and the range at which the even was felt has long baffled astronomers. If the cause of the event was a body from space, what was it made of and why did it explode with such force?

The primary theory is that an object made of stone and metals, an asteroid or meteor around 120 across, exploded. As it hurtled into the atmosphere, it was heated and heated the air that surrounded it to tens of thousands of degrees. The forces at work caused the object to fragment, and the debris exploded.

One new theory is that the object was a comet, not an asteroid. A comet would be composed mostly of frozen gases and water, rather than stone or metals as an asteroid would. The atmospheric effects created by the event suggest a body composed of similar materials that were dispersed during the plunge through the atmosphere and in the final explosion.

There are those who theorize that the Tunguska event was much more than the chance action of a piece of space debris. Some maintain that an explosion of such magnitude, equivalent to that from a nuclear device, could only have been made by an intelligence. A flying saucer exploded over remotest Siberia that day.

The Tunguska event damage is still visible in the region. The atmospheric effects, the earth tremors and the shock wave that summer morning in 1908 bore witness to the power of what happened. We may never know for sure what lit the sky that day.

Learn more about this author, Charles Simmins.
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