Scientists make a date for a close encounter with an asteroid in 2030

It may not prove the end of the world as we know it, but it could be a close-run thing. For the first time, scientists are formally predicting that the Earth could be hit by an asteroid, scheduled to arrive 30 years from now.

September 21st, 2030, is the date pencilled in for the arrival of 2000 SG344, a lump of space debris the size of an office block that could strike our planet with the force of 100 Hiroshima atom bombs. Scientists have been tracking the asteroid from observatories in Italy, Finland and the US in recent weeks.

The International Astronomical Union (IAU) is predicting a "close encounter with a non-negligible chance of future impact" with a 1-in-500 chance of hitting the Earth.

Previous asteroid scares have caused widespread alarm but proved to be unfounded, but this is the first time that a potential collision has been predicted following a scientific review process.

No one knows what SG344 is made of, as it was only discovered last September. Best estimates put its size at between 30 and 70 metres in diameter. If composed of loose gravel, it would probably disintegrate upon entering the Earth's atmosphere. But if the asteroid is made of stone and iron, it could explode with an estimated energy of two megatons.

Other speculation suggests that it could be a man-made rocket booster dumped during the Apollo era, which could also prove harmless.

Scientists are also investigating the possibility that even if SG344 misses the Earth in 2030, it could impact in subsequent orbits.

The IAU says it does not intend making any further statements on the possibility of an impact by SG344, but will leave it to individual scientists who are observing the asteroid.

The solar system is filled with hundreds of thousands of asteroids, almost all of them harmless to life on Earth.

On average, one strikes the Earth every 100 years. In 1908 a small asteroid, about 80 metres across, exploded above an unpopulated area of Siberia, producing a fireball that knocked people off their feet 40 miles away and flattened millions of trees.

Scientists have a few months to learn more about SG344 before it moves out of range for almost three decades. When it comes near the Earth again in 2028, it could be too late.