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by Steve Connor, Science Editor in The Independent

For the first time, astronomers have tracked an asteroid in space in the hours immediately before it collided with the Earth's upper atmosphere in a dramatic explosion.

The 80-tonne object – known as 2008TC3 – was the size of a small lorry and was spotted by astronomers on 6 October 2008.

Just 20 hours later it exploded with the force of about 1,000 tonnes of TNT 41 miles above the Nubian desert of Sudan, scattering fragments of meteorites across north-east Africa.

As soon as it was realised that the asteroid was on a collision course with Earth, astronomers from 26 observatories across the world scrambled to ensure that their instruments gathered as much information on it as possible before it was almost completely vaporised in the explosion.

The scientists not only managed to predict precisely when and where the collision would take place, but they also recovered nearly 280 pieces of the meteorite for chemical analysis. "This was an extraordinary opportunity, for the first time, to bring into the lab actual pieces of an asteroid we had seen in space," said Peter Jenniskens of Nasa's Seti Institute in California.

"This asteroid was made of a particularly fragile material that caused it to explode at a high altitude, before it was significantly slowed down, so that the few surviving fragments scattered over a large area. The recovered meteorites were unlike anything in our meteorite collection up to that point," Dr Jenniskens said.

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