A HUGE asteroid which is on a course to miss the Earth by a whisker in 2029 could go round its orbit again and score a direct hit a few years later.

Astronomers have calculated that the 1,000ft-wide asteroid called 2004 MN4 will pass by the Earth at a distance of between 15,000 and 25,000 miles — about a tenth of the distance between the Earth and the Moon and close enough to be seen with the naked eye.

Although they are sure that it will miss us, they are worried about the disturbance that such a close pass will give to the asteroid’s orbit. It might put 2004 MN4 on course for a collision in 2034 or a year or two later: the unpredictability of its behaviour means that the danger might not become apparent until it is too late.

As a safety precaution, some experts are calling for 2004 MN4 to be “tagged” with a transponder that would constantly radio its position. Scientists hope that this would provide enough warning to allow emergency action if necessary, possibly by diverting the object away from the Earth.Other instruments on the probe could provide information about its composition.

Benny Peiser, from Liverpool John Moores University, who is an expert on asteroid hazards, said: “We don’t know what that asteroid is made of and that might influence the way it’s affected by the Earth’s gravitational pull. There are other close approaches, in 2034 and 2035. In all likelihood it will produce an orbit that will not intercept the Earth, but we don’t know.”

The asteroid is big enough to cause damage on a regional scale, with an expected impact equivalent to a 1,000-megatonne explosion. It was discovered last June and its orbit plotted in detail by December. Startled astronomers calculated at one point that its chances of a direct hit on Friday, April 13, 2029, were 1 in 38. But additional calculations have set those fears to rest. The asteroid is now expected to miss but come close enough to be below the altitude of TV satellites. It should be visible as a rapidly moving point of light.

Brian Marsden, of the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, expects the close encounter to increase the frequency of the asteroid’s orbit, creating the possibility of further close encounters every five to nine years.

An interceptor mission is feasible and Dr Peiser said that an opportunity would arise in 2012, when 2004 MN4 will be ten million miles from Earth. “That’s not a big distance as far as space missions go,” he said.

“This is most likely not the object with our number on it, but one day we will have to address this question and we’ll need the technology. A transponder mission should not be too complicated or costly, and would provide a lot of vital data.”

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