World 'must tackle space threat'

The international community must work together to tackle the threat of asteroids colliding with Earth, a leading UN scientist says.

Professor Richard Crowther's comments come as a group of space experts called for a co-ordinated science-led response to the asteroid threat.

The Association of Space Explorers (ASE) says missions to intercept asteroids will need global approval.

The UN will meet in February to discuss the issue.

In the ASE report, the group of scientists and former astronauts point to the historical record to highlight the dangers of asteroids; an impact 65 million years ago may have wiped out the dinosaurs, and the Tunguska impact in 1908 produced a 2,000 sq km fire in Siberia, big enough to engulf a city the size of New York.

They say the next major threatening event could occur in less than 20 years. Asteroid Apophis is due to pass close to the Earth and analyses suggest a one in 45,000 chance of a collision.

An impact by Apophis would generate the equivalent of a 500 megatonne blast, at least 100 times more powerful than the Siberian event. ...
The document says most asteroids entering the Earth's atmosphere are small and burn up before reaching the surface. But it is the larger ones - perhaps 200m or more across - that would need to be deflected away from a collision course with the Earth.

The researchers propose several ways of doing this, the most extreme methods being to crash a spacecraft into the asteroid to knock it off course, or to set off a nuclear explosion. They say the earlier the threat is dealt with, the less drastic the course of action need be.

Professor Crowther says the natural forces of gravity can be used to deflect asteroids in many situations.

"We can use the natural attraction of a probe to one of the bodies, to slowly pull the object away."

He says if done at sufficient distance from the Earth, the orbit of an asteroid can be changed slightly to take it away from a collision path. .... -  bbc