In the early hours of yesterday morning a fireball exploded with the equivalent of a thousand tonnes of TNT over northern Sudan. The light was so intense that it lit up the sky like a full moon and an airliner 1,400km (870 miles) away reported seeing the bright flash.

The explosion was caused by an asteroid the size of a boulder roughly three metres (10ft) across. It sounds catastrophic, but the rock was totally annihilated as it smashed into the atmosphere, and there was no chance of it hitting the ground. In fact, asteroids this size hit the Earth’s atmosphere every few months or so. But this particular event was special because the asteroid was spotted before it blew up, the first time this has been achieved. The asteroid was seen by astronomers on Sunday at an observatory in Arizona, as part of a Nasa project to scan for approaching space rocks.

There are 5,681 such near-Earth objects, but only 757 of them are considered large enough to cause any damage if they hit Earth. If a dangerously large object were spotted in time the hope is to give enough warning to evacuate any people living in the likely crash zone, although the logistics involved would be mind-boggling.

However, it would be difficult to escape a 300m space rock. These strike every 60,000 years or so, and could trigger a monster-sized tsunami if they hit the sea. And an asteroid measuring more than a kilometre in diameter strikes Earth roughly every few hundred thousand years. This would obliterate everything in and around the impact zone and send the world’s climate into such turmoil that civilisation as we know it would collapse.