After fifty years of space exploration, humanity has left well over 5000 tons of debris up there, and the ever growing pile of space junk poses a serious risk to spacecraft. Now there's a solution...and it's only slightly crazy.
Space debris is generally characterized as either large enough to be tracked or too small to be seen, with the cutoff placed at around 10 centimeters across. There's estimated to be just under 20,000 pieces of large junk, 500,000 pieces between 1 and 10 centimeters, and tens of millions that are smaller than a centimeter across. Even these very small pieces can pose a serious risk to functioning spacecraft because they all travel at such high speeds, which makes the fact that we can't actually track them even more problematic.
That's where Gurudas Ganguli and his colleagues at the US Naval Research Laboratory enter the picture. His idea is to send up many tons of the metal tungsten up into space. This tungsten, which would be in dust form, would then be spread throughout the upper atmosphere so that it eventually formed a thin cloud around the entire planet. The tungsten would then start sticking to the tiny space junk, and because tungsten is so heavy it would push the junk to fall back towards Earth, where both would burn up in reentry.
Here's the big problem with the idea - there's no guarantee that the tungsten would make us any better off. If the tungsten dust started coalescing into balls of metal, they would remain up in orbit and become still more space junk for us to contend with. In fact, they might even form a minor ring system around Earth much like those found around the gas giants. Admittedly, that's actually kinda cool, but it would still only add to the dangers of continued space exploration.
The fact of the matter is that, in all likelihood, there's only one sure-fire way to get rid of the space junk, and that's to hope that someone soon sees the potential financial rewards of becoming an outer space garbageman. That's more or less how our terrestrial trash collection problems have always been solved, after all.