THE CHANCE OF BEING HIT BY SPACE JUNK...

My Herald on Sunday column... a pile of space junk...

The passengers on the LAN Chile flight from Santiago to Auckland last week should know just how close they came to calamity when a number of mysterious burning objects roared past during their journey over the Pacific last week.

If the burning objects had hit the plane, causing it to crash, they'd have been very unlucky indeed.

Experts are still arguing about whether the objects were pieces of Russian space junk or a meteorite, but the incident has highlighted the often-overlooked fact that we have made a dumping ground of not only our planet, but also of the heavens above.

Scientists estimate the chance of being hit by a piece of space junk that has re-entered the Earth's atmosphere is less than one in a trillion.

Like the Everest climbers who leave their trash, discarded equipment and the bodies of their unfortunate companions on the mountain, the explorers of space have thought little of discarding spent fuel tanks, rocket boosters and nuclear reactor cores and leaving their ageing satellites and space stations to fall apart.

The result is that millions of pieces of debris, some the size of a grain of sand, others the size of a bus, form a cloud around the earth.

Nasa can easily detect the larger pieces of junk, but the smaller fragments of flaking paint or frozen satellite coolant are too numerous to avoid and can be as lethal as a speeding bullet as they hurtle around the earth, posing a risk to the many satellites and space craft that are still functional.

Some 8000 satellites orbit the planet, and with private companies and countries alike seeking to put more satellites into space - in the name of exploration, Star Wars-like defence and to aid satellite communications - the clutter is only going to increase.

The Center for Orbital and Reentry Debris Studies estimates that 5400 tons of equipment has re-entered the earth's atmosphere in the past 40 years, the largest item of which was the Russian Mir space station, which weighed 135 tons and burned up on re-entry over the South Pacific - where most of the space junk is directed when its owners take the proactive step of "de-orbiting" - sending it back to earth.

Most space junk is conveniently vaporised when it is drawn into the earth's atmosphere, but some particularly solid bits, generally stainless steel, titanium and glass, survive burning in the massive heat created by the friction of metal against the atmosphere, and these actually splash down.

Or crash down, as the case may be. Spare a thought for the Ugandan family whose home in the city of Kasambya was hit in March 2002 by a titanium pressure sphere from the re-entering Ariane 3 rocket booster. Luckily, no one was home at the time.

While raining space junk isn't causing too many headaches for Nasa, and while the threat of meteors to humans is much greater than that of space junk, the space organisation does keep a close eye on re-entering debris and tries to pinpoint the time of re-entry and therefore the likely locations at which any surviving debris might land.

Scientists have also being working on ways to clean up space, and the Terminator Tether is one of their more intriguing proposals.

It consists of a 5km electrodynamic tether, a sort of lightweight wire that's wound up tightly and bolted to the side of a satellite.

At the end of the satellite's life, the tether is unwound, and it is charged with a current from the earth's magnetic field that drags the satellite back to earth, where it burns up - or provides a stunning light show for some terrified airline passengers.

Xbox elitism

Microsoft will this month release the Elite version of its Xbox 360 console, which includes a HDMI connector to connect to high definition TV screens. A 120GB hard drive will also be offered as an optional extra for US$180 (NZ$250). The Elite will have a black case, and while the inclusion of HDMI puts it on an even footing with the PS3 in terms of HD connection options, the Elite will not feature a HD-DVD drive for playing high-definition discs. Microsoft has yet to reveal local pricing, saying the Elite will be available this winter in limited supply.

Price: US$480 (NZ$670)