Taskforce urges action on threat from asteroids

A taskforce of government-appointed advisers urged Britain yesterday to take seriously the threat of a devastating collision between the Earth and a giant asteroid or comet.

A taskforce of government-appointed advisers urged Britain yesterday to take seriously the threat of a devastating collision between the Earth and a giant asteroid or comet.

Although the absolute risks may be small, the results would be so severe that it could affect everyone on the planet and have dire repercussions for the economy, life and even our future survival.

An object 1km (0.62 miles) wide could easily wipe out one-quarter of the world's population and even if the probability of such collisions was one every 100,000 years, the risks would still exceed the current safety standards used by industry, says the report of the Taskforce of Potentially Hazardous Near-Earth Objects.

"If such risks were the responsibility of an operator of an industrial plant or other activity, then that operator would be required to take steps to reduce the risk to levels that were deemed tolerable," the report says.

The three-man taskforce was set up last January by Lord Sainsbury of Turville, a Science minister, to establish the potential threat posed by near-Earth objects whose orbits could cause them to collide with the planet.

Professor David Williams, past president of the Royal Astronomical Society and a member of the taskforce, said the threat was genuine. "The point is that these impacts are of very low frequency but of very high consequence."

An object is classified as potentially hazardous if its orbit comes closer than 7.5 million km (4.6m miles) to Earth, which is roughly 20 times the distance between the planet and the Moon. So far astronomers have detected 258 objects in this category, but the number is increasing all the time as surveys of the sky continue. Scientists are confident that all of the 400 known asteroids larger than 1km in diameter do not pose a risk.

"However, it is estimated that a similar number of objects of this size have yet to be discovered," the report says.

"For smaller objects - which also cause great destruction locally or regionally - we know even less. For example, we have discovered fewer than 10 per cent of objects with a diameter of 300 metres, [and] a much smaller proportion of 100-metre objects," it says.

The taskforce wants moreinternational co-operation in surveys of the sky, and a new £15m telescope to be built in the southern hemisphere to search systematically for objects down to 300 metres wide.

It also wants the government to seek the support of other countries in studying possible ways of intercepting an incoming asteroid - either by nudging it away with rockets or blasting it with a nuclear device.

Harry Atkinson, the chairman of the taskforce and former council chairman of the European Space Agency, said he was confident that governments would find the resources necessary to deflect an incoming asteroid should one be detected. "I think the prospect of imminent death would concentrate the mind remarkably," he said.

The report says: "Given warning of decades or centuries, new technological developments would almost certainly emerge. The taskforce believes studies should now be set in hand on an international basis to look into the practical possibilities of deflection ... The longer the time before an impact, the more effective even a small nudge would be. This is not science fiction."

Comets and asteroid can travel at speeds ranging from 15km per second to 75km per second, which is more than 100 times faster than Concorde. The impact resulting from even a relatively small object is enormous - one 50-metre wide asteroid exploded over Siberia in 1908, flattening 2,000 square kilometres of forest.

Even if an asteroid fell into the ocean, it would cause a huge tsunami, or tidal wave. A 100-metre wave created when an asteroid fell into the coast off South America 2.15 million years ago had a devastating impact on Japan and West Africa.

"For an island country, the risks from tsunami effects are significant because of the large target area of the surrounding ocean," says the taskforce, the third member of which is Sir Crispin Tickell, the former British ambassador to the UN.