Bonzer Words!: Space Junk
"Not content with polluting the earth, mankind is now creating a cosmic junkyard,'' declares Wendy Ogbourne.
I bet you think that space is more or less empty. If you take a trip to the moon, you're not going to meet much on the way. Well, yes and no.
There are currently over a thousand objects that have been sent into orbit round the earth for a specific purpose—weather and telecommunications satellites, probes and other equipment for taking photos of the earth, looking at everybody and everything, and of course the International Space Station. But as well as these, there are about 18,000 bits of space junk, and nobody knows quite how many. Most of these are in low earth-orbit, between 850 and 1000 km above the earth and are officially tracked by NASA.
What are they? Anything from jettisoned fuel tanks and discarded parts of spacecraft, to nuts and bolts and paint chips. It has become fashionable to have one's ashes sent into space orbit. One of the Gemini 4 astronauts, Ed White lost a glove, which is still out there. More than 200 objects are known to have been released by the Mir space station, plain garbage in plastic bags. Not content with polluting the earth, mankind is now creating a cosmic junkyard.
Though these pieces are mostly quite small, they are all travelling at around 22,000 mph. At this speed, even a 1 mm metal chip can do as much damage as a .22-caliber rifle bullet. Colliding with a pea-sized sphere would be like hitting a 60 lb safe at 60mph. If a spaceship or its fuel tanks should be hit by one during take-off or re-entry, the result could be devastating.
Most of these fragments will eventually fall back towards earth as their orbits decay, and will burn up harmlessly in the atmosphere. However, the larger ones will either hit the surface in one piece, or break up and scatter over a large area. The chances of a person actually being hit by a piece of debris are put at 1 in 1 trillion, and there is only one recorded incident where this has happened. The earth is a big place and objects landing in desert areas will not even be noticed. In 1979 the Skylab space laboratory crash was uncontrolled, but pieces landed safely across outback Western Australia and in the Indian Ocean. But the possibility of chunks of metal falling on a populated area or into the ocean, with the risk of causing a tsunami is a real concern.
The US government launched a missile to destroy an ailing spy satellite, the size of a school bus. It was a tricky exercise, but was considered safer to destroy it now, rather than wait for it to re-enter the atmosphere at some unknown future date. The project went off without a hitch. This may be the course taken with other potentially dangerous objects, as there is a growing call to clean up the area of space surrounding our world.
Talking about things falling out of the sky, there are also asteroids.
Asteroids are chunks of rock, left over when the solar system was formed. They come in all shapes and sizes, and have long and often very erratic orbits around the sun, which occasionally bring them close to earth. Collisions with asteroids have been frequent throughout earth's history, and it is probable that one caused the extinction of the dinosaurs. There are 600 asteroids which could be potentially hazardous to us, and these are all closely monitored, and their orbits known, though smaller ones do sometimes slip through.
The media love a Near Miss story, even when there is actually no danger at all. In September 2004, Toutatis, the largest known asteroid at 2.9 miles long, passed within 1 million miles, about four times the distance of the moon. An encounter this close only happens once every 1300 years. In February this year there were reports that we were about to be hit, but the 'disaster' passed without most of us even being aware of it. In 2029, for those who are still around to see it, Apophis, 400 metres in length will pass at a distance of only 3 earth diameters. It is doubtful whether it will be visible to the naked eye, but astronomers are looking forward to such a rare opportunity to view an asteroid at such close quarters.
So when you think of 'empty space', remember all our silent companions who join us in our endless journey round the galaxy.
© Wendy Ogbourne
Wendy writes for Bonzer! magazine. Please visit www.bonzer.org.au
