Be prepared the end is near, scientist warns

The lifetime risk of dying after a massive asteroid impact is about the same as dying in a plane crash. While visits by giant comets and asteroids are rare, their potential for destruction is so huge and involves so many people that governments around the world should be preparing for them.

Dr Duncan Steel of the University of Salford left visitors to the British Association's Festival of Science in no doubt about the dangers posed by near earth object (NEO) impactors. Yet little is being done either to locate dangerous NEOs or develop ways of stopping them.

"Nobody seems to be doing anything about it," he said. "They are a significant hazard to humans and are at least as bad as the risk of an aeroplane crash."

Legislators and the public generally dismiss the issue, saying that a major impact hasn't happened since the days of the dinosaurs, he said. Yet this is a false view because little work is being done to find the really big impactors, and no one is doing this in the Southern Hemisphere.

A potentially devastating asteroid called Hermes shaved close to the Earth in 1937, he said, but was quickly lost from view. "It certainly could come back to earth" but scientists don't know where to look for it. "It is like having a dart board and we are the bulls-eye."

Scientists estimate that we currently spot only about half of the most dangerous NEOs and significantly only 1 per cent of the very faint but destructive 100-metre-diameter objects. These are often disregarded, despite their one-in-100 chance of arriving in any given year.

A 100-metre-wide body blew up over Tunguska in 1908. The resulting explosion flattened 2,200 square kilometres of forest, he said, and a similar detonation over Marble Arch in central London would destroy or damage everything out as far as the M25 ring road.

There is an annual one-in100,000 chance of an impact with an object over one kilometre, but a body that size would be expected to wipe out at least a quarter of the world's population depending where it struck. Dr Steel calculated the risk at about a one-in-20,000 risk of dying, comparable to the lifetime risk of death in a plane crash.

A Southern Hemisphere impact by a giant NEO could be a possibility given the lack of observation there, he said. Assuming Australia was hit, it wouldn't take long for us to realise something bad had happened.

The end of the world as we know it would come with clusters of earthquakes, existing geological fault-lines shaken loose by the impact which would register a 12 on the Richter Scale, Prof Steel said. About 45 minutes later a rain of burning rocks would shower down on us, material ploughed up and ejected by the impact.

The greatest risk however would be the poisoning of our atmosphere, he said.