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Saturday, 4 November, 2000, 22:15 GMT
Scientists revise asteroid warning
Asteroid Nasa
A Nasa impression of an asteroid hitting the Earth
By BBC News Online science editor Dr David Whitehouse

Astronomers say reports that the Earth could be struck by a small asteroid in 2030 are wildly exaggerated.

Less than a day after sounding the alert about asteroid 2000SG344, a revised analysis of the space rock's orbit shows it will in fact miss the Earth by about five million kilometres (three million miles).

However, astronomers will continue to monitor the asteroid, which was picked up in September and thought to be 30 - 70 metres (100-230 feet) across.

Some scientists have criticised the way the information was released to the media before it had been thoroughly confirmed.

Threat rating

Asteroid 2000SG344 is the first object to have a threat rating of greater than zero on the 0-10 Torino scale of dangerous objects from space.

It was spotted on 29 September by astronomers David Tholen and Robert Whiteley using the Canada-France-Hawaii 3.6-metre telescope on the island of Hawaii.

Shortly thereafter, pre-discovery observations taken in May 1999 by the Linear sky survey were also identified.

On Friday, the International Astronomical Union issued an alert saying that the object had about a 1-in-500 chance of striking the Earth on 21 September, 2030.

No object has ever been rated with so high a chance of impact.

Were it to strike our planet, the results would be devastating, with an explosion greater than the most powerful nuclear weapon.

Sky survey data

But after the announcement, astronomers began looking at sky survey data to see if the object had been picked up but not recognised in earlier observations.

This turned out to be the case and these past observations allowed a more accurate calculation of the asteroid's orbit to be made.

The result: in 2030, the space rock will miss us by about five million kilometres, or 12 times the distance from the Earth to the Moon.

The new orbit reveals a slight risk of a collision with the Earth about 2071, but it is thought that when the orbit is better known this risk will disappear as well.

Currently, asteroid 2000SG344 is about 15 million kilometres (nine million miles) away and getting more distant.

'Premature and alarmist'

Because 2000SG344 is in a similar orbit to the Earth, it has been suggested that it might be an old Saturn upper-stage rocket of the type that was used in the early Apollo Moon missions.

If it is manmade and did strike Earth, the effects would be very local and limited.

Some scientists have criticised the IAU and Nasa for releasing warnings about the asteroid only for those warnings to be rescinded less than a day later.

Benny Peiser of Liverpool John Moores University, UK, said it was "extremely unwise, premature and alarmist".

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