We know that space junk is a problem, but could it completely cut off our access to space? Astronomer Mark Thompson gives his opinion.
It's two months since that infamous meteor streaked behind me on BBC Stargazing LIVE, and I still get reminded about it, but I'm not bitter (honest). I was even filming the other night and the cameraman said he spotted another one shoot behind me! If I were superstitious (which I'm not), I might be getting a little concerned that the Universe was having a laugh at my expense.
It can be very easy for the untrained eye to assume that these things seen whizzing through the sky are natural meteors. However, it turns out that every year, approximately 200 kilograms (440 pounds) of man-made meteors plummet through the atmosphere and are most likely misidentified as natural pieces of space rock.
It's a worrying prospect, but with increasing levels of space junk, it's not just us down here on the surface that are at increasing risk of some of those pieces of junk actually hitting the ground (although the vast majority of space junk is tiny and burn up harmlessly in the atmosphere). Astronauts in orbit are incredibly vulnerable to the stuff and if unchecked, we may eventually become cut off from space by our own celestial equivalent of barbed wire.
We've been exploring space now for a little over 50 years and in that time we've left behind a trail of junk from bags of astronauts waste, to bits of rockets and even the famous toolbag dropped by spacewalking astronaut Heidemarie Stefanyshyn-Piperduring during a 2008 NASA mission to the International Space Station (ISS).
It is a sobering thought that millions of pieces of debris are thought to be in orbit right above our heads and tracking them is posing a bit of a problem. The real worry isn't the sheer quantity of all the junk we can see and track, but it's the junk that we can't see. Pieces smaller than a golf ball can cause serious damage and it's virtually impossible to detect and monitor them.
Traveling at speeds of a hundred times faster than a commercial airliner means they posses an incredible amount of destructive energy and are perhaps the greatest risk to space travel.
With over a thousand satellites in orbit, the situation isn't likely to get any better in the near future. It just takes one satellite to explode or collide with another -- which happened a few years ago when a defunct Russian satellite hit an operational U.S. Iridium satellite, shattering it into hundreds of pieces -- or be hit by a stray fragment that generates even more junk and traveling at supersonic speeds.
With every collision, or generation of debris, comes an increased risk of more and more collisions. This mechanism even has its own name: the "Kessler Syndrome."
This repeated collision mechanism was described in 1978 by NASA scientist Donald J Kessler who envisaged a scenario in which the density of objects in low-Earth orbit could become high enough that collisions between objects could cause a cascade with each collision generating debris which increases the likelihood of further collisions.
If we don't tackle the problem, there is a real chance that in a couple of hundred years time, we may well cut off our access to space, a hideous thought, thanks to Kessler Syndrome.
But is there anything we can do? Well, there have been some ideas such as building a giant "space sieve" or a balloon covered in glue which orbits the Earth, gently sweeping up junk that comes close. Unfortunately, innovation in space junk collection is in its infancy.
So for now, without any realistic propositions, it seems all we can do is monitor the big bits and keep our fingers crossed that we avoid the smaller pieces!
