The object, catalogued as 2008-TC3 and estimated to be up to five metres across, streaked into view of astonished astronomers on October 6, as it raced towards Earth.

It was the observatory at Mount Lemmon, near Tuscon in Arizona, which first spotted the object, who then sent word around the world to fellow observers.

And travelling at over 29,000mph, they didn't have much time to do the necessary calculations.

In total, 570 astrometric and almost as many photometric observations were fired off in less than 19 hours, and reported to the Minor Planet Center.

Impact predictions were performed by University of Pisa's CLOMON 2 semi-automatic monitoring system as well as Nasa Jet Propulsion Laboratory's Sentry system, which warns of potential impacts.

When the asteroid finally reached the atmosphere above Sudan, it created an enormous flash which was observed by the pilots of a KLM flight more than 750 miles away.

Incredibly, the orbiting Meteosat weather satellite captured images of 2008-TC3 exploding, which experts said had the energy of a two-kiloton nuclear warhead - the same as 2,000 tonnes of dynamite.

Infrasound detector arrays in Kenya also detected a sound wave from the direction of the expected impact.

Fortunately for the inhabitants of Planet Earth, nothing substantial reached the ground.

Don Yeomans, from Nasa JPL's Near-Earth Programme Office, said: "A very small, few-meter sized asteroid, designated 2008-TC3, was found Monday morning by the Catalina Sky Survey from their observatory near Tucson Arizona.

"Preliminary orbital computations by the Minor Planet Center suggested an atmospheric entry of this object within a day of discovery.

"JPL confirmed that an atmospheric impact will very likely occur during early morning twilight over northern Sudan, north-eastern Africa, at 2:46 UT Tuesday morning.

"Objects of this size would be expected to enter the Earth's atmosphere every few months on average but this is the first time such an event has been predicted ahead of time."

The impact of 2008-TC3 has echoes of the so-called "Eastern Mediterranean Event" of June 6, 2002.

It involved a high-energy aerial explosion of a nine-metre asteroid over the Mediterranean Sea, between Libya and Crete, Greece.

Unlike this week's event, the asteroid went totally undetected while approaching the Earth.

The explosion was also detected by satellites and seismographic stations, with a calculated yield of about 26 kilotons of TNT - about double the yield of the Hiroshima bomb.

Had it burst on a populated area, the consequences would have been catastrophic.

Earth sits in what can be termed a 'cosmic shooting gallery', with thousands of Near Earth Objects passing close by every year.

Only a few, however, stray uncomfortably close.

The monitoring of 2008-TC3 this week, even at such short notice, is a good indication that the world-wide 'Spaceguard' alert system is working, experts say.

A 50-metre asteroid is due to pass within seven lunar distances of Earth today (Friday).

One of similar size, which actually made it to the surface, created the Barringer Crater, otherwise known as Meteor Crater, near Flagstaff, Arizona, in the United States.

That one exploded with the force of 150 atom bombs, and left a crater about 1,200m (4,000ft) in diameter and 170m deep (570ft), surrounded by a rim that rises 45m (150ft) above the surrounding plains.