The rapid increase in debris drifting above Earth, left behind as old satellites have broken up or even collided, is contributing to a growing problem that has planners at the US space agency Nasa worried about future safety.
Now a new satellite, launched on Friday night from the Vandenburg USAF base in southern California, will map the proliferation and density of the pieces of debris, which are circling Earth at about 17,000mph.
The particles range in size from pebbles to microscopic motes. Yet their terrific speed, relative to objects rising from Earth, means that they can pack a terrible punch - enough to puncture or disrupt sensitive equipment. The Hubble Space Telescope and the Space Shuttle have both been hit - though not seriously - by space junk. In the Shuttle's case, an orbiting fleck of paint left a visible pit in one of its windows.
The problem is worsening too because collisions between pieces of junk in turn produce more potentially lethal missiles.
"Many of these particles are produced by collisions between larger debris objects, and so information about these particles is important for understanding the whole debris population in Earth orbit," said Bruce McKibben, the senior scientist at the University of Chicago's laboratory for astrophysics and space research. His team designed the instrument that will search for the debris.
The satellite will also try to distinguish between the amount of space junk left behind since the Soviet Union put Sputnik into space in 1957 and cometary dust and rocks left by the passage of celestial objects.
"This is the first active experiment where you can separate these two phenomena," said John Simpson, a professor emeritus at the University of Chicago. "We will be able to tell whether the debris is uniformly distributed or in "clouds" around the Earth, and even whether there's a ring of it around the Earth."
The current data about space junk were gathered by satellite between 1984 and 1990, but are now hopelessly out of date. There are known to be about 6,000 items of space junk larger than 10cm - but smaller pieces are just as dangerous to huge projects such as the International Space Station.
The new satellite, called Argos, will circle Earth for three years at an altitude of 516 miles in a region heavily used by commercial, scientific and government spacecraft. Ground tracking suggests that debris is particularly concentrated at that height. It would of course be bad luck if Argos was itself a victim of space junk. Indeed, the controllers might seem to be tempting fate: in November it will be used to monitor the intensity of the Leonid meteor shower, which may reach a 33-year high.Reuse content