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updated 9/30/2011 6:19:59 PM ET 2011-09-30T22:19:59

Just last week, NASA's Upper Atmosphere Research Satellite (UARS) came crashing down into the Pacific Ocean. It had broken into 26 pieces and, weighing in at a total of 500 kg (1,100 lb), it would have certainly created a splash.

The satellite had reached the end of its useful life and it was left to atmospheric drag to bring it crashing back down to Earth. While UARS can't really be classed as space junk now, there are still over a million pieces of manmade debris still up in orbit.

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Perhaps you'd think it's best just left up there, out of our way; after all, it would just be more rubbish to get rid of down here and its not like it's causing any trouble, right? Wrong.

As UARS has reminded us, stuff in space does sometimes fall back to Earth and thankfully the chances of getting hit at any given moment are pretty slim. There is a much greater chance that debris will land in the vast oceans that cover 70 percent of the planet, or the dry arid plains of the deserts.

It seems we are pretty safe, but each year around 195,000 kg of space debris falls back to Earth, and it's on the increase! Do you feel lucky?

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Although a chunk of defunct satellite bumping you on the head might sound scary, it is an extremely remote possibility. By far the most worrying scenario is the increasing likelihood that big bits of space junk might start bumping into other big bits of space junk, creating a cascade of smaller and smaller pieces of menacing space debris.

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Satellite collisions are a great cause for concern, since their orbits are getting crowded. There are over a thousand satellites in a multitude of different orbits and on occasions, they collide. Just a few years back, a U.S. and a Russian satellite collided, destroying both and breaking them up into an estimated 500 pieces!

Collisions between satellites are rare, but when they do collide, a field of debris is created along the orbits of both satellites. Pieces the size of flecks of paint, when traveling 100 times the speed of a jet, can cause significant, even fatal, damage!

The "Kessler Syndrome" describes how this runaway cascading effect can ultimately lead to so much debris that humanity could be cut off from space. I know I wouldn't fancy space travel if I had to first go through a cloud of millions of tiny pieces of metal traveling at ballistic speeds.

ANALYSIS: Space Junk Problem Reaches 'Tipping Point'

Clearly there is an increasing chance of damage down here on Earth from falling debris, but there is an even greater danger to satellites in orbit. We rely on satellites more than you might realize for global communications, navigation, meteorology and much, much more. Destroy those and we loose an integral set of systems that we have come to rely upon.

Even the International Space Station isn't immune to the space debris problem. A few months ago, its inhabitants had to move to the emergency escape vehicles (the docked Soyuz spacecraft) due to a risk of collision with a piece of junk.

It's a sobering thought that not only have we left a pretty big scar on this planet, but it also looks like we are doing the same thing in space.

ARTICLE: What Can We Do About the Space Junk Problem?

The ultimate conclusion is grim: More pieces of debris -- some as large as UARS -- falling to Earth (increasing the risk of damage or public injury). But more sobering than that: We may end up cutting ourselves off from space, imposing a man-made impenetrable barrier around our planet that we won't be able to travel though.

© 2012 Discovery Channel

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