If you take a decent telescope and fix it in the direction of Saturn, you will gaze upon a magnificent spectacle. Like a pearl surrounded by a sliver of onyx marble, it is encircled by a pale disc of water ice, thinning and thickening at different radii to give the illusion of rings.

Earth, too, has its rings, but they are made of junk. Well, satellites. Some serve noble ends - giving us digital television, sat-nav, mobile phones, weather monitoring and, of course, a spyglass on rogue nations - but most are redundant. In the half century that we've been firing the things up, we have brought down only a handful.

So, the collision between an Iridium communications satellite and a spent Russian satellite at 800km above Siberia was an accident waiting to happen. The smash, at an altitude relatively close to Earth, sent a cloud of debris through space, posing a risk to some Nasa Earth-observing satellites and the nearby Hubble Space Telescope.

It's anarchy up there. The Space Surveillance Network, run by the US Defence Department, keeps tabs on everything over 10cm whizzing around the planet - at present about 17,000 objects -- partly to make sure that if one falls back to Earth, it isn't mistaken for a missile. But there is no space equivalent of the Highway Code (the Very Very Highway Code, perhaps) and no space traffic control. Instead, there is ad hoc communication between satellite operators along the lines of “Our satellite is failing, you'd better get yours out of the way”.

About 6,000 satellites have been launched since Sputnik in 1957; the number of countries launching their own hardware is growing (Iran just joined the club) and private operators are proliferating. Some retirees get kicked up to a higher graveyard orbit, but even here, they eventually break up and tumble to lower orbits.

You don't need whole satellites to create havoc - bits and pieces, even paint, peel off all the time, and float off on their own destructive odysseys.

The chance of a disaster is low but not trivial, and climbs every time a new satellite is sent heavenwards. Space debris tops the list of hazards to the International Space Station. Even a penny-sized fragment, hurtling through space at 22,000km/h, could cause it to depressurise. The station has had to perform eight “collision avoidance manoeuvres” in its ten-year history; thankfully, this incident doesn't really threaten it (its orbit is about 400km below the danger zone).

A scarier incident was in 2007, when debris from a Russian satellite narrowly missed an aircraft carrying 270 passengers. It brings a whole new meaning, but not a welcome one, to the idea of Soviet fallout.

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