[Phobos Grunt, Russia's Mars probe, is currently floundering in Earth's orbit and is at risk of breaking up in our atmosphere. But the imperiled craft is far from alone up there]

Once upon a time the heavens were pristine and perfect. Humanity, with its propensity to surround itself with life's detritus, was firmly tethered to the ground, so it looked like the space on Earth's doorstep would remain forever untainted. Then, someone had the bright idea that mankind could shake free of his Earthly shackles and the age of space junk was born.

Since then, humanity has been given the opportunity to build a heavenly extension to his Earthly landfill site and now, – just fifty years since he dropped his first orbital crisp packet – the space around Earth has become a bit of a junkyard.

In fact since the launch of Sputnik in 1957, mankind has lofted more than 6,500 satellites into god’s backyard. Add to that some spent rocket stages and other bits and bobs travelling at more than 28,000 kilometres per hour and (one or two collisions later) you have swarm of space debris more numerous than the locust visited upon Ancient Egypt (and far more dangerous).

[Image above: A model of all the space junk in Earth orbit large enough to be tracked. ESA]

Just a few months ago the inhabitants of the International Space Station were forced to evacuate to their Soyuz lifeboat as a swarm of potentially ISS-disabling debris honed into view. More recently, in October, a German satellite, Rosat, plunged to Earth and scattered debris across the Bay of Bengal and, in September, a NASA upper atmosphere research satellite (UARS) shuffled off its mortal coil and crashed into the Pacific Ocean.

[Graphic: How much space junk is there and how dangerous is it? – Click to blow up]

But space debris is more than just a passing danger to equipment – even a tiny flake of paint becomes a potentially deadly projectile when travelling at orbital speeds. The risk to the Space Station and the astronauts that occupy it taken very seriously by Nasa – in fact it has been estimated that in the lifetime of the Station there is a one in 12 chance that an astronaut will be killed by space debris. This wasn’t the first time the Space Station has been threatened by hordes of marauding space junk and, since 1999, it has had to change its orbit about a dozen times to step out of the way.

The risk to commercial satellites is also well documented and, with several high-profile loses in the last two years alone, space junk is problem that is going to have to addressed sooner or later.

In September, the National Research Council published a 180-page report on NASA’s efforts to reduce the risk posed by space debris. They recommended that orbital debris programmes should be given greater investmnet and that NASA (and other space agencies) must sharpen up their long-term debris modeling systems and improve their ability to measure and track space junk. There are some international guidelines in place that concern the reduction of space debris, but they don't address into whose lap the responsibilty for cleaning it all up will fall.

After all, if we have this much junk littering our doorstep so soon after the dawn of the space age, what’s Earth going to look like by the time Star Trek becomes a reality?