Sat, Dec 10, 2005 - Page 9 News List

`Evil' asteroid hurtles toward Earth

There is very little time left to decide how to deal with the 390m wide rock that could crash into the planet



In ancient Egypt, Apophis was the spirit of evil and destruction, a demon that was determined to plunge the world into eternal darkness.

A fitting name, astronomers reasoned, for a menace now hurtling toward Earth from outer space. Scientists are monitoring the progress of a 390m wide asteroid discovered last year that is potentially on a collision course with the planet and are imploring governments to decide on a strategy for dealing with it.

NASA has estimated that an impact from Apophis, which has an outside chance of hitting the Earth in 2036, would release more than 100,000 times the energy released in the nuclear blast over Hiroshima. Thousands of square kilometers would be directly affected by the blast, but the whole of the Earth would see the effects of the dust released into the atmosphere.

And, scientists insist, there is actually very little time left to decide. At a recent meeting of experts in near-Earth objects (NEOs) in London, scientists said it could take decades to design, test and build the required technology to deflect the asteroid.

"It's a question of when, not if, a near-Earth object collides with Earth," said Monica Grady, an expert in meteorites at the UK's Open University.

"Many of the smaller objects break up when they reach the Earth's atmosphere and have no impact. However, a NEO larger than 1km [wide] will collide with the Earth every few 100,000 years and a NEO larger than 6km, which could cause mass extinction, will collide with the Earth every 100 million years. We are overdue for a big one," she said.

Apophis had been intermittently tracked since its discovery in June last year, but last December it started causing serious concern.

Projecting the orbit of the asteroid into the future, astronomers had calculated that the odds of it hitting the Earth in 2029 were alarming. As more observations came in, the odds got higher.

Having more than 20 years warning of potential impact might seem plenty of time. But, at last week's meeting, Andrea Carusi, president of the Spaceguard Foundation, said that the time for governments to make decisions on what to do was now, to give scientists time to prepare mitigation missions.

At the peak of concern, Apophis asteroid was placed at four out of 10 on the Torino scale -- a measure of the threat posed by an NEO where 10 is a certain collision which could cause a global catastrophe. This was the highest of any asteroid in recorded history and it had a 1 in 37 chance of hitting the Earth.

The threat of a collision in 2029 was eventually ruled out at the end of last year.

"When it does pass close to us on April 13, 2029, the Earth will deflect it and change its orbit," said Alan Fitzsimmons, an astronomer from Queen's University Belfast.

"There's a small possibility that if it passes through a particular point in space, the so-called keyhole, ... the Earth's gravity will change things so that when it comes back around again in 2036, it will collide with us," he said.

The chance of Apophis passing through the keyhole, a 600m patch of space, is 1-in-5,500 based on current information.

There is no shortage of ideas on how to deflect asteroids. The Advanced Concepts Team at the European Space Agency (ESA) have led the effort in designing a range of satellites and rockets to nudge asteroids on a collision course for Earth into a different orbit.

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