The low Earth orbit, located 2,000 km above the Earth's surface, has the highest concentration of space debris. (NASA)Space junk is the common term for debris that orbits the Earth - anything from the remains of old booster rockets to the tool bag that drifted free from a space-walking astronaut outside the space station in November 2008. These bits and pieces range from very small to very large, but they travel at very high speed and even the smallest ones can pose a threat to satellites and manned craft. Here's a by-the-numbers look at the whirring and perilous state of space junk circling our planet:
600 — pieces of debris estimated to have been released into space in the collision between the U.S. communications group Iridium Satellite LLC and a Russian Cosmos-2251 military satellite.
200 metres/second (720 km/hour) — speed at which satellite debris is travelling.
A pea-sized piece of debris measuring one-centimetre travelling at 10 km/second has the same kinetic energy as a 250-kg dumpster whirring along at 100 km/hour, according to NASA.
17,000 — number of debris measuring at least 10 centimetres orbiting the Earth, according to 2008 data from the United States Strategic Command.
900 — number of pieces of debris created when China destroyed its Fengyun 1-C satellite in January 2007.
The number of objects measuring between one and 10 centimetres is greater than 200,000, according to NASA's Orbital Debris Program Office.
NASA also notes most orbital debris is located within 2,000 km of the Earth's surface and travels at an average speed of about 10 km/second (36,000 km/hour).
100 years — approximate amount of time that the debris in orbits that are more than 1,000 km above the Earth's surface will continue to travel around the Earth before re-entering the atmosphere. Debris travelling in orbits below 600 km falls to Earth after several years. At altitudes below 400 km, the debris is likely to fall to Earth before it has even been detected or identified.
30 km/hour — the estimated impact velocity of a light piece of debris falling to Earth. The velocity for larger objects is 300 km/hr, according to the Center for Orbital and Reentry Debris Studies.
About three out of every four payloads are not operational, according to a 2008 NASA report.
$100,000 — value of a tool bag lost during a spacewalk in November 2008. Heidemarie Stefanyshyn-Piper lost the bag, which was not tethered, as she attempted to mop up grease that spilled out of a grease gun.
36,000 km — altitude at which most telecommunications and meteorological spacecraft rest.
One in one trillion — odds that a person will be struck and injured by a piece of space debris, according to the Center for Orbital and Reentry Debris Studies.
