Scientists hunt for asteroids

An asteroid impact would shake the planet

"The dinosaurs were just not smart enough to spot their nemesis coming and do something about it - but we are," says Dr Duncan Steel, an expert in the detection of meteors, asteroids and comets.

We are going to have revenge on a comet called Tempel 1

Peter Schultz, Nasa

The scientist from Salford University, UK, warns that humans must learn the lessons from 65 million years ago, when it is thought the impact of a giant space rock on the planet accelerated the end of the dinosaur dynasty.

"I think it would be grossly stupid of us not to tackle it head-on," he told the BBC's World Service's Discovery programme.

Much research is being done to investigate how the Earth might protect itself against any future strike. But with much of the southern hemisphere sky unpatrolled by asteroid and comet-seeking telescopes, it is clear our efforts to stave off some future, apocalyptic event could be stepped up.

Global disaster

To date, there is no record of anyone having been killed by an asteroid impact but the devastation that would be caused by a large one is so terrible that, statistically, you are more likely to die from a space-rock impact than in a plane crash.

The dinosaurs could do nothing about it - could we?

When an asteroid called 2001 YB5 whizzed past the Earth on 7 January, 2002, it missed the planet by more than half a million kilometres (300,000 miles) - but, at the speed the Earth is travelling in its orbit, that distance accounts for only a few hours.

2001 YB5 was probably 300 metres (980 feet) across. When a large body estimated at only 50 metres (160 feet) in size exploded above the Siberian forest in 1908, it flattened trees over a wide area.

A less frequent threat but one that could be even more deadly and even harder to predict is that of a comet.

Nasa action

Comets come from the frozen outer reaches of the Solar System and are very difficult to spot before they reach the distance of Jupiter, by which time it could be too late to plan a defence. So what are scientists doing to prevent collision?

A third of the sky is currently not being searched because there is no Southern Hemisphere search programme

Dr Duncan Steel, Salford University

An ambitious Nasa space probe under construction plans to strike back as project worker, Peter Schultz of Brown University, Rhode Island, explains:

"We're going to have some revenge on a comet called Tempel 1 with the Deep Impact mission."

The Deep Impact mission hopes to reveal the nature of the threat and how to deflect it safely.

On American Independence Day 2005, Deep Impact will reach its target, the six-kilometre diameter comet Tempel 1.

The space probe will release a 350-kilogram (770 lbs) projectile into the heart of the comet at 10 kilometres per second (six miles per second). It is expected to blow a crater the size of a football field and 20 metres (65 feet) deep.

The comet will survive but should reveal the nature of its interior to add to scientific knowledge and to guide any future plans to deflect a killer comet with a nuclear nudge.

'Back door' omission

The search for comets and asteroids is stepping up.

So far, it is centred in the USA, though teams in Japan and Britain are setting up information centres and may adapt telescopes in the Canary Islands to join the search.

The Deep Impact craft could tell us how to destroy a comet

But a telescope powerful enough to see a small asteroid can only search a small strip of sky at a time and at present no one is searching in the southern hemisphere.

This worries Dr Duncan Steel, who used to run a search programme in Australia.

"A third of the sky is currently not being searched because there is no Southern Hemisphere search programme," he warns.

"In essence, at the current time, our back door is open because no one is looking down there."