A three-year study of litter in space has shown that Nasa scientists appear to have miscalculated the amount of debris travelling around our planet at heights of between 800 and 1,000 kilometres above the Earth's surface.
Nasa's estimates of the total amount of hi-tech litter varies between 20,000 and 70,000 pieces, as only larger objects can be individually tracked by the North American Aerospace Defence command network, Norad. It includes bits of old rockets, dead satellites, particles of aluminium, mainly from American solid rocket boosters, as well as millions of microscopic particles, including tiny flecks of paint.
The extra high-altitude material has baffled the agency, which thought it had accounted for all sources of junk at these altitudes. Its scientists cannot explain where the extra space flotsam has come from. Steven Young, editor of Astronomy Now, said it would be relatively easy for Nasa's computer simulation of space junk to have missed out a source. 'It is most likely to be a stage of a rocket not previously identified as a source of litter.'
Nasa's radar survey of space junk was carried out by a team at the Massachusetts Institute of Technology. It produced another surprise result - at low orbits space is apparently getting cleaner. At heights of about 500 kilometres from Earth, Nasa found there is only about half the amount of debris it forecast 10 years ago. This is welcome news for the international space station, Alpha, which will sit at about this altitude. An encounter with a piece of space junk, could be disastrous for Alpha. Even a pea-sized fragment orbiting at an average speed of 18,000mph could shatter a satellite. In 1991, a space shuttle had a near-miss when it had to swerve to avoid the remains of a Soviet Vostok rocket.