Bolts, old screwdrivers, plastic bags, paint, broken pens, bent CDs - they are the kind of objects you would expect to find in a list of rubbish. Except that this collection of litter is not to be found in the bin at the end of the front garden, but whizzing about in space, threatening to collide with astronauts.

Astronomers working for the European Space Agency (ESA) warned yesterday that space is so full of rubbish that it has become a danger to the people and satellites in it. A team from the Canary Islands Institute of Astrophysics predicted that it will have detected around 100,000 fragments of space rubbish by the time it has finished a definitive catalogue.

The detritus it has found consists of defunct satellites, spent rocket stages and other debris from spacecraft, either jettisoned deliberately, or broken off as a result of explosions or collisions. Equally dangerous are the tools that have been dropped by astronauts while performing external maintenance work.

Any artificial object orbiting the earth can be a nuisance, even plastic bags, pens and CDs.

"Rubbish in space is no threat to the earth's population since it doesn't tend to fall and if it does, it breaks up in the atmosphere because of the friction," Miquel Serra from the institute, told EFE, a Spanish news agency. "The danger is for missions in space."

Old bits of satellite and astronauts' spanners can reach speeds of thousands of miles an hour as they fall through space, so the smallest pieces of debris can do serious damage to a satellite or spacecraft. Flecks of paint from satellites have been known to cause pits half a centimetre deep in the windows of the US space shuttle.

Mr Serra's team, based at the Teide observatory in Tenerife, is working alongside the Astrophysics Institute from the University of Berne in Switzerland on a project sponsored by ESA to produce an exhaustive catalogue of space rubbish. So far they have detected more than 2,500 pieces of space rubbish of 20-25cms (about 8ins-10ins). The study could take another 10 years to complete.

Mr Serra said that objects of this size could prove fatal for astronauts working outside their vehicles. As well as detecting new rubbish, the team tracks known objects to establish their orbits.

Space rubbish is not a new phenomenon. The astronaut Edward White lost a glove during the first American spacewalk in 1965. But the space around the earth is getting increasingly congested.

There are now more than 600 working satellites and most of the rubbish that has been detected is in a near-earth orbit, up to about 1,200 miles above the earth's surface, the altitude most useful for satellites.

In 2002, ESA's European Space Operations Centre in Darmstadt, Germany, estimated that the amount of space debris increases by 5% a year. A conference in Darmstadt in 1997 concluded that because of technical and economic restraints, nothing could be done to clean up the rubbish.

ESA is exploring other ways round the problem. It is looking at producing smaller satellites that will burn up on re-entry and positioning satellites further from the earth, beyond the most congested orbits.

The most spectacular piece of space rubbish to fall to earth was Skylab, which broke up as it re-entered the atmosphere in 1979, six years after it was launched. One part fell into the Indian Ocean and another piece hit Australia.