An ASTEROID big enough to flatten London will narrowly miss the Earth today, scientists have said.
Experts believe reassuringly there is no chance of the 150ft-wide space rock hitting the planet, but it could come as close as 17,200 miles - placing it within the orbits of more than 100 telecommunication and weather satellites.
The asteroid, given the catchy name 2012 DA14, has been closely tracked since its discovery by a Spanish observatory a year ago.
It is predicted to reach its nearest point to Earth at around 7.30pm UK time today.
Sky watchers have been told that given clear skies they should be able to track the rock climbing in the north-eastern sky from anywhere in the UK.
Robin Scagell, vice-president of the Society for Popular Astronomy, said: “It will be possible to see it if you know where to look, but just waving your binoculars in the right general direction isn't going to work.
“The asteroid will be a faint dot of light moving at a steady rate between the stars. It'll be thousands of times fainter than Jupiter and 250 times fainter than the stars of the Plough.
“The trick will be to find the area in advance and wait for it to come through. You can use the star maps to find exactly the right part of the sky. If you hold your binoculars steady you will see this tiny point of light crawling across your field of view in about seven or eight minutes.
“It's not easy, but you will have the thrill of knowing you are seeing a little object in space the size of an office block.”
DA14 will take two hours to travel between the constellations of Leo and the Plough from 8pm.
Travelling at between 12,427mph (20,000kph) and 18,641mph (30,000kph) - around five miles (8km) a second, or eight times the speed of a rifle bullet - the asteroid will fly inside the orbits of high geostationary satellites some 22,000 miles (35,406km) above the Earth.
Astronomer and asteroid expert Dr Dan Brown, from Nottingham Trent University, said: “There are loads of them but you're talking about a very big area. It would be very unlucky if a satellite was hit. The asteroid is more likely to hit some space junk, but most of this is only about a centimetre across and the impact won't even be noticed.”
Precise calculations show there is absolutely no possibility of DA14 hitting the Earth.
But scientists have a good idea of what the effect of such an impact would be because a similar-sized meteor devastated a remote region of Siberia in 1908.
Exploding a short distance above the ground over Tunguska, the object generated a blast 1,000 times more powerful than the atom bomb dropped on Hiroshima. Forest was completely flattened over an area of 830 square miles (2,150 sq km).
During today's fly-by, scientists will use radar to study DA14 and learn about its composition and structure. The knowledge could prove useful if steps have to be taken to remove the threat of another space rock.
The “Hollywood option” of blowing up an incoming asteroid has been ruled out by experts. Such a solution would only result in deadly debris raining down on Earth.
Instead, scientists are looking at ways of gently nudging an asteroid onto a safer trajectory.
The American space agency Nasa has plans for a future mission called Dart which will fire a probe at an asteroid to see if it can be moved.
Fewer than 10,000 of the asteroids which could one day pose a threat to the Earth have so far been identified.
This is less than 10% of all the objects that may be out there, according to Dr Lindley Johnson, head of Nasa's Near Earth Objects observations programme.