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Friday, 5 April, 2002, 09:27 GMT 10:27 UK
Asteroid could hit Earth in 2880
Meteor Crater, Nasa
It would leave behind a hole 20 times bigger than Meteor Crater in the US

A one kilometre-wide chunk of space rock could strike the Earth in 2880, say astronomers.

The asteroid, designated 1950 DA, has a one in 300 chance of colliding with our planet, according to calculations. The situation will become clearer once more precise data on the rock's orbit in the Solar System are obtained.

Scientists say this is not something people should get too concerned about.

If an impact became a real possibility, humanity would have several decades to work out how to give the rock a gentle nudge to take it away from the planet.

Lost and found

1950 DA was first detected on 23 February, 1950, by astronomers at the Lick Observatory in California, US. But after just 17 days of observations the rock was lost from view.

1950 DA, Nasa Jpl
Radar reveals the profile of 1950 DA
It was picked up again on 31 December, 2000, by the Lowell Observatory Near Earth Object Search (LONEOS) program.

And subsequent radar observations from the Arecibo and Goldstone radio telescopes during the asteroid's most recent close approach to Earth - about 20 lunar distances from the planet - allowed astronomers to refine the rock's orbit.

The calculations indicate that 1950 DA will have its closest pass to Earth on 16 March, 2880 - how close has still to be determined.

Quick rock

"This is not something to worry about," said Jon Giorgini, a senior engineer at the American space agency's Jet Propulsion Laboratory.

"We're showing that searches with optical telescopes and follow-up observations with radar telescopes can provide us centuries of advance notice about potential close encounters of asteroids with Earth.

Body, BBC
Devastation: A space body laid waste to a large part of Siberia in 1908
"That's plenty of time to consider the options - 35 generations, in fact."

The data on 1950 DA suggest it is travelling at a velocity of about 15 km (nine miles) per second relative to the Earth.

This means that if 1950 DA were to collide with the planet, it would do so with an explosive force of approximately 44,800 megatonnes of TNT.

If it struck land, it would produce a crater about 22 km (14 miles) across, with a blast radius of intense damage of around 300 km (190 miles).

Small but deadly

If the impact occurred in the ocean, a tsunami 25 metres (80 feet) high would be generated 1,000 km (620 miles) from the impact site.

Currently, 1950 DA has been rated as a level two event on the Torino warning scale, which means it is an event "meriting concern".

Experts say the size of the asteroid is close to that which could affect the Earth's global climate.

However, it is not thought a collision with 1950 DA would threaten the continued existence of our species.

By comparison, the impact 67 million years ago, which has been implicated in the extinction of the dinosaurs, is thought to have been caused by an object 10 times the diameter of 1950 DA.

Small force

Given the relatively small size of 1950 DA and the 878 years' advance warning, it would be possible to alter the orbit of the object if it was considered necessary.

One method would rely on the Yarkovsky effect. This describes what happens when an asteroid radiates energy absorbed from the Sun back into space.

Releasing heat in one direction nudges the asteroid in the opposite direction. The resulting acceleration is tiny, but over the centuries acts like a weak rocket and could make the difference between a hit and a miss.

Humanity could try to roughen up one side of the 1950 DA with explosives or by dusting it with chalk to change the way the asteroid reflects light.

Research data on 1950 DA are published in the journal Science.

 WATCH/LISTEN
 ON THIS STORY
The BBC's Fergus Walsh
"It is by far the biggest known threat from space"
See also:

01 Jan 02 | Science/Nature
08 Nov 01 | Science/Nature
23 Jul 99 | Science/Nature
12 Apr 01 | Science/Nature
03 Jun 98 | Science/Nature
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