ASTEROID hunters spent the Christmas holiday worrying that a 400-metre object might hit the Earth in 2029.

Asteroid 2004 MN4 circles the sun every 323 days, spending much of its time inside Earth's orbit. It was discovered in June, but because it was observed for only two days, estimates of its path were imprecise.

After it was spotted again on 18 December, automated computer systems sounded the alarm, and on 23 December NASA's Jet Propulsion Laboratory and the University of Pisa in Italy announced a 1 in 300 chance of impact in 2029. By 27 December the risk of impact was calculated as 1 in 38 - the highest ever.

Then Jeff Larsen of the Spacewatch project at the University of Arizona found that the project's telescopes had spotted the asteroid as far back as 15 March. With the extra data, JPL and Pisa calculated the asteroid would not hit the Earth, although its most likely path is just 60,000 kilometres away, one-sixth the distance to the moon.

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