Wherever the human race goes, we seem to leave a trail behind us - it's become our calling card. At the moment there are hundreds of thousands of pieces of man-made space flotsam, orbiting the earth, everything from tiny fragments of paint to whole satellites.

And in recent years this space pollution has escalated. NASA now has a thousand extra little fragments to watch and it employs people like Dr William Ailor, at The Center for Orbital and Reentry Debris Studies in Los Angeles, to track the movement of each bit and to catalogue them. Dr Ailor told Earth Beat why space junk is a serious problem.

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