Possible impact effects based on energy Nature of the Tunguska bolide
And, because about 100 million people live within 2 km of a shoreline, large ocean impacts have the potential to cause severe tsunami devastation. Once the initial heat pulse has passed, micron-sized dust particles and vapour condensates in the atmosphere may take characteristically between 1 and 10 years to settle down, collapsing food chains in the meantime. Everywhere on the surface of the Earth, the sky is red hot and a global conflagration results. Above a certain energy (˜10 6 Mt), vaporized material thrown out from the impact punches out through the atmosphere and spreads globally. The threshold for a civilization-destroying impact, killing over a billion people, comes in at a 1 or 2 km diameter bolide. The occurrence of 20 impacts from a fragmented comet, D/1993 F2 (Shoemaker-Levy 9), on Jupiter as recently as July 1994 demonstrates that planetary impacts are common at high energies too - the characteristic energy of the fragments was about 100 000 Mt ( Asphaug and Benz 1996), enough to cause devastation on continental scales on Earth.Įstimates, all of them uncertain, have been made of the damage expected from impactors of various sizes (see table 1). On the other hand, seismic and barometric data have consistently been interpreted as pointing to a higher impact energy, typically 10-15 Mt ( Ben-Menahem 1975). It might have been as low as 3 Mt (megatons TNT equivalent) - some simulations suggest this, with fierce vortex winds responsible for destroying an already weak Siberian forest. The impact energy of the event remains uncertain. The political ramifications that would have followed the destruction of Edwardian London are a matter for speculation one may question whether the British Empire would have survived. An incandescent column of matter would have been thrown 20 km into the air over London, and the city itself would have been destroyed about as far out as the present-day M25 ring road. People would have had their hats knocked off in Glasgow and Edinburgh, topsoil would have been stripped from fields in Cheshire, trains would have been derailed throughout central England, and people in Oxford would have been thrown through the air and severely burned. The gunfire-like bangs of the impact would have been heard across Britain to Ireland, north to Orkney and Denmark, and over Europe as far as Switzerland.
In the case of an impact on London, a bolide brighter than the Sun, and leaving a thick trail of smoke, would have been seen approaching from half way across France. It is occasionally pointed out that if the 1908 impact had taken place over a metropolitan area, huge damage would have been inflicted. The explosion due to an incoming cosmic body over the Tunguska region of Siberia in 1908 flattened trees over 2000 square km.