'Killer' asteroid threat to Earth
By David Derbyshire
 

PLANS to save the world from a catastrophic asteroid collision were unveiled yesterday by British scientists.

Experts urged the Government to create an early warning system to stop the sort of disaster that wiped out dinosaurs 65 million years ago. The Near Earth Objects task force also called for more research into ways of deflecting life-threatening objects away from the Earth.

 "Armageddon asteroids" capable of causing mass extinction are rare, arriving once every few million years. But asteroids and comets large enough to wipe out a city hit the Earth every couple of hundred years.

 In 1908, a meteor exploded above Lake Tunguska in Siberia, destroying 770 square miles of forest. If the same explosion happened above St Paul's Cathedral, it would destroy London. So far, astronomers have identified 258 potentially hazardous objects in the Solar System but say there are many hundreds more.

 Yesterday's report was prepared by Dr Harry Atkinson, past chairman of the European Space Agency's Council, Sir Crispin Tickell, Britain's former ambassador to the UN, and Prof David Williams, a past president of the Royal Astronomical Society.

 Nasa is seeking out every object larger than one kilometre but wants Britain to take a lead in the search for smaller objects. Dr Atkinson said: "The risk is very small. A one-kilometre asteroid arrives on average every 100,000 years. But if that was the risk of an accident in a nuclear power station, we would spend a lot of money to reduce the risk."

 Britain was urged to seek partners to build a £15 million three-metre telescope in the Southern Hemisphere capable of observing objects a few hundred yards across. It would be the first in the world devoted to seeking out near-Earth objects.

 It also called for existing ground and orbiting telescopes to be used to detect objects and more research into deflecting asteroids. One possibility would be to fire explosives or a metal projectile from an unmanned space craft to nudge an asteroid out of the way.

 A model for this could be Nasa's Deep Impact 1 mission, due to be launched in 2004, which will fly alongside comet Tempel 1 and hurl a half-ton lump of copper on to its surface. Another option is to attach solar sails to an asteroid to change its orbit. Nuclear explosives would be a last resort because of the danger of blowing it into smaller, but still dangerous, pieces.

 A 100-metre object hits the Earth every 10,000 years with the force of a 100-megaton nuclear bomb and every 100,000 years an object strikes with a force equivalent to 10 million Hiroshima bombs. If the impact is in the sea, it can trigger tidal waves. If on land, it can send dust and soil into the atmosphere, blocking off the sun.