Page last updated at 16:04 GMT, Thursday, 8 October 2009 17:04 UK

Asteroid collision 'less likely'

Artist's impression of Apophis (SPL)
Rest easy: the asteroid only has a four in a million chance of Earth impact

Refined calculations of the asteroid Apophis's path show it is far less likely smash into Earth in 2036 than was previously thought.

Earlier calculations put the probability of a collision at one in 45,000; the revised estimate puts the odds at one in 250,000.

Researchers from the US space agency Nasa showed that in 2029, Apophis will pass within just 30,000km of Earth.

The work will be presented at a meeting of the American Astronomical Society.

The new calculations are based on more precise measurements of the asteroid's position based on images captured by Dave Tholen at the University of Hawaii, supplemented by further measurements by telescopes in Arizona and Puerto Rico.

Researchers at Nasa's Jet Propulsion Laboratory (JPL) used these revised position measurements to refine the estimates of the asteroid's proximity in its future Earth flybys.

Artist's impression of Apophis (Dan Durda/FIAAA)
Orbits the Sun every 324 days, crossing Earth's orbit twice
Not spherical, diameter of 300m; a mass of 27 million tonnes
Name: Ancient Egyptian god Apep ('The Destroyer')
Discovery: In 2004 by a University of Hawaii team

Another pass in 2068 has a three-in-a-million chance of striking Earth, but the researchers say that as the measurements are more completely refined, the chances of that collision will drop further.

Rather than a catastrophic scenario, the far more likely near-misses provide great research opportunities.

"The refined orbital determination further reinforces that Apophis is an asteroid we can look to as an opportunity for exciting science and not something that should be feared," said Don Yeomans, manager of the Near-Earth Object program office at Nasa's Jet Propulsion Laboratory.

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