Asteroid gives Earth a cosmic 'close shave'

BY MARK HENDERSON, SCIENCE CORRESPONDENT

Danger from outer space

THE Earth has had a cosmic near miss with an asteroid one third of a mile wide, leading to new calls for an international task force to devise ways of preventing a devastating impact.

The 2000 QW7 asteroid, which originated in the belt between Mars and Jupiter, passed within 2.4 million miles of the Earth on Friday morning, astronomers said yesterday. It was detected at Cornell University's Arecibo Observatory in Puerto Rico, six days before it hurtled past the Earth.

The asteroid was only twelve times further away than the moon when it reached the nearest point to earth on its orbit - a close shave in cosmic terms.

Lembit Opik, the Liberal Democrat MP who has campaigned for international co-operation to counter the dangers of asteroids, said that the Earth had had a very narrow escape. "It is as if someone had thrown a marble at you across a tennis court and missed your head by the width of your hand," he said. "It is all very well saying it didn't hit us, but if it had been 2.4 million miles this way, which is peanuts, we wouldn't be here talking about it today."

The near miss underlined the need for international co-operation to share information on the extent of asteroid threats and to work out means by which dangerous asteroids could be destroyed or diverted, he said. Astronomers said that the discovery of 2000 QW7 was highly significant as it offered an exceptional opportunity to study a potentially hazardous asteroid (PHA) at close quarters.

"This is a very importat object," said Eleanor Helin, principal investigator at Nasa's Near Earth Asteroid Tracking system (Neat), on Maui, Hawaii. "It's so bright that astronomers can track it now and through to the end of the year. It's a bit of a mystery why we haven't seen this one before." Asteroids are classified as PHAs if they are larger than a couple of hundred metres across, and have orbits within 4.65 million miles of the Earth.

Gravitational nudges by the Earth, Mars or Jupiter could alter their orbits, and set them on a collision course with our planet. Any such impact would be devastating to life on Earth, and could wipe out up to a quarter of the human population. An asteroid seven miles wide that hit the Yucatan peninsula 65 million years ago, in what is now Mexico, is widely accepted to have caused the extinction of the dinosaurs and three quarters of the other species living on the planet.

An asteroid about 60 metres across landed at Tunguska in Siberia in 1908, flattening trees for 13 miles and killing hundreds of reindeer. Had the impact been in the centre of London, everything inside the M25 would have been destroyed. Scientists say that if an asteroid the size of 2000 QW7 - which is nine times as large as the Tunguska asteroid - were to hit the Earth, the devastation it would cause would be frightening. If it landed in the Atlantic Ocean, everything within two miles would be vapourised and the east coast of the United States and the west coast of Europe would be swept by tidal waves. Molten debris would continue to rain down for weeks after the impact, and dust particles would cause effects similar to a nuclear winter".

Mr Opik said: "It would not be as bad as the dinosaurs, but you might estimate that one in four of the world's population would die in the end."

Both the British and US armed forces are believed to be studying ways in which an asteroid could be blasted off course by nuclear attack.

http://www.the-times.co.uk/news/pages/tim/2000/09/05/timfgname01001.html

-- Martin Thompson (mthom1927@aol.com), September 05, 2000