Space Junk, Debris: Cleaning Up Outer Space: Kessler Syndrome A computer generated graphic shows space junk orbiting Earth. There is a lot of stuff floating around in space that we put there and simply forgot about. There are old satellites that stopped working, bits of the rockets that put them there and even the odd astronaut's leave-behind. That's potentially catastrophic news for our continued presence in space. It's bad enough that today's satellites risk running into something up there, but if we aren't careful, the problem will spiral out of control and leave orbit too hazardous for even the hardiest spacecraft. In space even the tiniest particles can cause a lot of damage. The laws of physics are the same, but the speeds involved are far outside our everyday experience. This means things we would brush off on Earth can become terrible threats in orbit - a speck of space dust can damage a spacecraft and put astronauts' lives at risk. A piece of debris no bigger than a centimetre can destroy a spacecraft. That's because of the high relative speeds that objects in orbit can attain. It takes energy to deform and shatter metal and plastic, so the damage caused when two objects collide is in proportion to their energy of motion. A moving car is dangerous because it is heavy. A speeding bullet is dangerous because it is fast. In space, if you hit another object, it is likely to be travelling much faster than a bullet from a gun, and many of those objects are much heavier than bullets. Space debris occurs naturally thanks to fragments of asteroids, comets and other heavenly bodies. But by adding our own debris to the mix, we don't just increase the odds of hitting something, but risk a much greater problem known as the Kessler syndrome. At some point, the debris becomes so dense that a chain reaction of collisions begins. Big objects are broken into lots of smaller ones, which in turn go on to pulverise other big objects and so on. Now, instead of a few thousand large bits of debris that can be easily tracked, you have a vast, unpredictable cloud of little bits surrounding the planet. Some experts worry that the Kessler syndrome is just around the corner. Others think it may have already started. The fear of orbit becoming so debris-ridden it becomes too dangerous, has led to proposals to clean things up, including sending up specially designed robots to grab on to them and drag them back into the atmosphere to burn up. It's easier to get the big ones now, while they are intact, rather than trying to mop up all the pieces later if the Kessler syndrome gets to them.