Four years from now, 30 June 2008, will be the 100th anniversary of one of the most mysterious catastrophes: the explosion of a body from space near the Podkamennaya (or Stony) Tunguska River in Siberia. There can scarcely have been another event in the past century to compare with it. The total power of the explosion exceeded the combined power of the atomic bombs dropped on Hiroshima and Nagasaki more than 2,000 times over!

Apart from that, the Tunguska explosion caused:

• an anomalous glow in the sky that was observed as late as 10 days afterwards, and the intense appearance of silvery clouds;

• massive radiation of light and heat;

• disruption of the normal functioning of meteorological instruments and the appearance of surface earth tremors;

• a tremendous sound wave that travelled twice around the globe;

• the felling of trees over an enormous area of over 2,000 square kilometres;

• weak traces of radioactivity, detected in tree samples and the polar ice layers dating from 1908;

• anomalous properties of the soil and minerals in the area of the Tunguska explosion;

• the unusually rapid growth of vegetation at the epicentre of the Tunguska explosion;

• cooling of the Earth's climate in the following few years.

Despite the fact that such a tremendous event did not go unnoticed, the first attempts to discover what had actually occurred in the remote Siberian taiga were only made many years later, in 1927. Since then, dozens of research expeditions have visited the area, hundreds of scientific papers have been written and several hundred hypotheses put forward about the causes of the event. Not one of them, however, has been able to explain fully the complex phenomena that preceded and accompanied the Tunguska explosion. Some of the phenomena observed by eyewitnesses simply do not fit within the framework of existing theories. Much of what happened then cannot be interpreted at all from the standpoint of present-day scientific thinking.

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