Early on the morning of 30 June 1908, the vast forest of western Siberia was illuminated by a strange apparition: an alien object streaking across the cloudless sky. White hot from its headlong plunge into the Earth’s atmosphere, the intruder exploded about 8 km above the ground, flattening trees over an area of 2000 square kilometres.
Despite the huge detonation, equivalent to a 10 megaton nuclear warhead (about 500 times the energy of the Hiroshima atomic bomb), there were few if any casualties in the sparsely populated taiga. If the Tunguska object – probably an asteroid about twice the size of a tennis court – had exploded over London or Paris, the list of casualties would have run into millions.
Fortunately, cataclysmic events caused by incoming near-earth objects (NEOs) are few and far between. Current estimates suggest that a 50 metre Tunguska-like object is likely to collide with the Earth once every 100-300 years. A 1 km object, which typically arrives every few hundred thousand years, could wipe out an entire country. An impact in the ocean would be no better, generating enormous waves (known as tsunamis) that would devastate coastal areas thousands of kilometres away.
Franco Bonacina | alfa
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