PACE : may seem empty, beautiful and boundless, but in the immediate neighbourhood of Planet Earth it is quickly resembling an ugly junkyard.

Scientists are dismayed at the debris that is pilling up in orbit less than 45 years after man launched the first satellite, Sputnik.

"There are more than 100,000 objects in orbit, of which only 600-700 are sperational satellites, "says Walter Flury, the European Space Agency's co-ordinator on space debris. "There are no internationl laws about the debris problem and you cannot clean it up. It's that simple."

The trash includes tiny fragments from exploded boosters, lens covers that have dropped off satellite cameras, enormous fuel tanks, Soviet-era nuclear powered satellites, dripping sodium and potassium coolant from their decrepit hulls, drifting nuts, bolts, screwdrivers nd srenches accidentally dropped by space-walking astronauts.

The risk of collision with this trash is statistically remote, but it is increasing as more countries join the space powers, and any kmpact can be catastrophic.

In about 4,000 rocket launches, there has been only one documented case of a serious incident. That happened in 1996 when a French spy satellite, Cerise, was whacked at about 50,000 km per hour by a wheeling fragment left from an exploded Ariane rocket.

Experts say they fret most over the smaller items, some of which can be impossible to track by radar and telescope from Earth.

The Web site space.com reports that NASA had a major scare last November, when a Russian spy satellite, Cosmos 2367, which had been lofted in December 1999, broke up in more than 300 pieces, 40 percent of which were thrown into orbits that crossed the path of the ISS.

In June 1983, the wind screen of US shuttle Challenger had to be replaced after it was chipped by a fleck of paint measuring 0.3 mm, which impacted at 4 km per second.

The worst debris clouds are in two main areas, in Low Earth orbit (LEO), which is at an altitude of between 800 and 1,500 km above the Earth, and in geostationary orbit, about 35,000 km away. That is a problem. These are precisely the areas earmarked for the global navigation and telecommunications satellites that are the force behind the digital revolution.

Toughening the casings of satellites and solar panels so that they resist an impact or shifting their position to avoid drifting debris is an enormous financial drain, says Flury.

Once the rubbish is up there, it tends to stay there. Something in geostationary orbit can be there for hundreds of years. Rubbish in LEO is gently plucked by gravity and contact with air molecules on the fringes of the atmosphere and sometimes comes down after only a few years, burning up harmlessly on its descent.

What can be done about space garbage? The best that can be hoped for is to discourage further debris from adding to the pile, says Flury.

No international treaty addresses the trash problem, although the United Nations may adopt a set of technical guidelines next year which space faring nations will be encouraged to adopt.