Space debris, orbital debris or space junk, are the objects orbiting Earth. They consist of big, obsolete pieces of machinery like rocket boosters and satellites, to small parts such as paint flakes and other bits and pieces from explosions or wear and tear. Most of this debris is located in orbits with altitudes between 500 and 1,700 km from Earth.

Space debris has become a serious and a neglected problem of space exploration. In 1957, the world’s first artificial satellite, Sputnik I, was launched into space, and since then, numerous other space probes and satellites have been sent into orbit. Many of these orbiting satellites ceased working and were discarded into space along with pieces of floating debris generated from other probes that circled the Earth. At least eighty man-made satellites have broken up into smaller fragments.

At present there are over 40,000 pieces of useless, possibly hazardous space debris floating in earth’s orbit, most of which are at least the size of a golf ball. There are also billions of very small pieces, such as fragments of paint. This debris noiselessly revolves around the globe at speeds of up to 25,000 miles per hour with altitudes ranging from hundreds to thousands of miles.

This man-made debris isn’t only occupying its place in space but this useless junk is also present on the Moon, Venus and Mars. Some of these objects such as flags and plaques are left from space probes that landed on them. Four man-made NASA probes have been exploring land outside our solar system. They are named Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2. When these probes were launched in the 1970s, there was no plan of bringing them back. Their booster rockets are still orbiting the earth aimlessly and once discarded, they too will become space junk.

Debris that orbits the Earth can very easily hit space shuttles, space stations and vital man-made satellites. Even objects the size of a thumb pin can be dangerous. If a piece of metal the size of a thumb pin orbits the earth at 17,500 miles per hour and collides with a space shuttle that is moving at the same speed in the opposite direction, extensive damage can occur and if the object is larger, the destruction can be unimaginable.

In 1989, NASA scientists discovered a cloud of nuclear debris leaking from a Soviet space reactor that was used to power their spy satellites. There is a probability of other leaking reactors orbiting Earth and that these nuclear clouds could jeopardise further space exploration. This space junk can endanger space walks of an astronaut, as even minuscule pieces of debris can very easily puncture a space suit.

Space debris is also hazardous when it enters earth’s atmosphere. Nearly all pieces burn up once they enter the outer atmosphere, nevertheless, larger particles can break up and still reach the surface of the earth. Three-quarters of all debris that enters our atmosphere falls in one of the oceans and are no threat to humans, unless it is a part of a nuclear powered satellite. In 1978, parts a Soviet satellite named Cosmos 954 fell to the earth in northern Canada. In 1979, parts of the US Skylab satellite fell in the Indian Ocean and Western Australia. Fortunately these areas weren’t heavily populated and no one was harmed.

Scientists estimate that there are over a million bits of debris orbiting the Earth. About 70,000 objects about the size of a postage stamp have been detected at an altitude of 850 to 1,000 km above the earth’s surface. They are probably frozen bits of nuclear reactor coolant that are leaking from old satellites. Although most of the debris in space is small, they are travelling extremely fast. Below altitudes of 2,000 km, the average relative impact speed is 36,000kmph. At this speed, collision can be immense. A one millimetre metal chip could do as much damage as a 0.22-caliber long rifle bullet. A pea-sized ball moving this fast is as dangerous as a 400-pound metal safe travelling at 60 mph. A metal sphere the size of a tennis ball is as lethal as 25 sticks of dynamite.