Wednesday, May 19, 1999 Published at 17:16 GMT 18:16 UK

Close shave with asteroid

By BBC News Online Science Editor Dr David Whitehouse

A large asteroid could miss the Earth by only 38,000 kilometres in 2027, according to new astronomical observations. This is an extremely close shave - the Moon orbits 10 times further from Earth.

The calculations suggest that an impact is not possible that year but, in theory, the Earth's gravity could perturb the asteroid's path, possibly leading to an impact in 2039.

The near-miss trajectory of a newly-discovered asteroid, called 1999 AN10, was announced in April. Now, the observational data of Australian astronomer F. Zoltowski allows calculations of just how close the asteroid may come to Earth.

Closer and closer

Astronomers at the Minor Planet Center at the US Smithsonian Astrophysical Observatory used Zoltowski's work to work out an estimated approach distance for AN10 of 56,500 kilometres from Earth. The fly-by will occur on August 7, 2027.

But the closest possible distance that AN10 could come to the Earth on that day is only 38,000km.

The calculations suggest the asteroid will not impact. But the new calculations confirm the initial speculation that the asteroid might approach within the Earth's sphere of gravitational influence.

It could therefore be perturbed in such a way that it might impact some years later.

Impossible to predict

Dr Benny Peiser of Liverpool John Moore's University in England says that the chaotic behaviour of this asteroid makes it practically impossible to predict all possible approaches for more than a few decades after any close encounter.

He says the orbit will remain dangerously close to the orbit of the Earth for about 600 years.

Astronomers stress that a collision is only one of a range of possibilities for this kilometre-wide chunk of rock. If it did strike, it would cause continent-wide devastation and alter the Earth's climate.