Astronomers have discovered a mile-wide asteroid that could collide with the Earth in 40 years time.

If it did, the devastation would be continent-wide, with massive global effects for decades. Hundreds of millions of people would die and many animal species would be wiped out.

The object is called asteroid 1999 AN10 and it was discovered on 13 January. It was picked up by the Linear telescopic survey that scans the sky for so-called Neo's - Near Earth Objects.

1999 AN10 circles the Sun every 643 days and twice each year the Earth comes close to the giant rock.

From almost a hundred observations made of it since its discovery, astronomers have determined its orbit. Close approaches to Earth occur in 2027, but no impacts are possible then according to Andrea Milani and Steven Chesley of the University of Pisa.

But 2039 is a different matter.

Close monitoring

In calculating the orbit for 1999 AN10, the Italian astronomers say that for August 2039 "a collision solution actually exists."

It is important to note that this is different from a definite prediction of a collision.

In fact, from what is known at the moment, the probability of 1999 AN10 striking the Earth must be less than the probability of being hit by an undiscovered asteroid on a given day.

Nonetheless, now that the asteroid has been found, its orbit is attracting attention. The Italian astronomers say it will have to be monitored closely.

They add that it is conceivable that at some time in the future a decision could be made to deflect or destroy it just like in the movie Armageddon.

Website publication

Where has this announcement of major importance been made? Not in a press release but without much fuss on the astronomers' own Website.

Nasa is concerned about the way in which information gets out

Dr Benny Peiser of Liverpool's John Moores University, an expert in Near Earth Objects, has expressed concern that the news of 1999 AN10 was released on a Website without going through normal review procedures.

"There is no reason whatsoever why the findings about 1999 AN10 should not be available to the general public - unless they have not been checked."

He adds that, if they have not been verified, they should not have been posted on the web in the first place.

The reason why the Italian astronomers have released their worrying findings this way may be a reaction to stringent Nasa rules regarding the reporting of potential asteroid impacts.

Asteroid scare

Following a scare last year, when it was thought that asteroid 1997 XF11 may strike us, a claim retracted 24 hours later, Nasa has clamped down on what it calls the premature release of sensitive data.

1997 XF11 was a false alarm. It is unlikely that 1999 AN10 will hit us - but it cannot be ruled out completely at this stage.

Calculations suggest that this asteroid will remain "dangerously close" to Earth for the next 600 years.

According to Barry Peiser, what is worrying is not the chances of 1999 AN10 striking the Earth but the "unnecessary and detrimental secrecy that surrounds this object."

Other astronomers have said that the Italian astronomers have followed the correct procedure to distribute information about 1999 AN10 and that there is no reason at this stage why they should have made their observations public.