The Feb. 10 collision of a defunct Russian military satellite and a commercial American satellite in the skies approximately 800 km above Siberia — one of the most popular altitudes in low Earth orbit — is worrisome for a world that has grown to rely on satellites for everything from communications and navigation to scientific research and spying.

Taking place at a speed of approximately 42,120 km per hour, the collision turned the two satellites into a cloud of debris that is spreading over a vast area and could eventually ring the planet. It is this rubbish that has scientists, commercial enterprises and governments so concerned. As the amount of junk grows — in February NASA estimated there were some 19,000 objects present in Earth's low and high orbits, most of which were debris — so does the risk of damage to satellites, spacecrafts and astronauts.

It's easy to imagine space debris as junk merely floating around, but in reality it moves at an average speed of 10 km per second, posing a serious hazard to spacecraft, satellites and astronauts. A 5-cm fragment can strike with a force equivalent to that of a steel safe smashing into the ground after being dropped from a 10-story window. One chip of aluminum paint measuring 0.2 mm left a 4-mm crater when it struck the Space Shuttle Challenger's windshield in 1983.