BBC News
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| Artist's impression of the asteroid poised above London |
An asteroid
capable of wiping out a city has missed the Earth by an astronomical
whisker.
The 50-yard
space rock travelled over London at more than 20 miles per second
before missing the planet by just 480,000 miles - twice the distance
to the moon but a near miss in astronomical terms.
If it had
collided with Earth it would have left a hole three quarters of
a mile across.
The asteroid,
still visible through a reasonably powerful telescope in the constellation
of Ophiuchus, appeared without warning above the capital at 2400GMT
on Friday.
Robin Scagell,
vice-president of the Society for Popular Astronomy, said astronomers
can track kilometre-wide asteroids - but spotting smaller objects
is much harder.
"Not
long ago something like this would have been totally overlooked,"
he said.
"Now
with the advanced image detectors available today we are beginning
to realise that we're in a bit of a shooting gallery."
The asteroid,
which has been given the name 2000 YA, is big enough to have devastated
London, Mr Scagell added.
"An object
this size would leave a crater three quarters of a mile across,"
he said.
Devastated
London
"Imagine
that in Piccadilly Circus."
"We've
probably been quite lucky up to now.
"There
are probably thousands of objects of this size out there."
Professor
Duncan Steel, the author of Target Earth - a book about asteroids,
told the BBC Radio 4's Today programme: "The last time the
Earth was hit by something like this was in 1908 above Siberia.
"It released
energy equivalent to about 20 megatonnes of TNT.
"If
it was to enter the atmosphere above London, it would take out
the whole of the city out to the M25."
In September,
a government task force established to assess the threat of so-called
Near Earth Objects (Neos) called on ministers to seek international
partners to build a new £15m telescope dedicated to sweeping
the skies for threatening objects.
The three-metre
(9.8 feet) survey telescope, based in the Southern Hemisphere,
would be designed to detect objects down to a few hundred metres
across.
Other recommendations
of the official report included the setting up of an asteroid
defence centre in Britain and working with the international community
on ways to mitigate any future impacts.
The Liberal
Democrat MP Lembit Opik, who campaigned for the task force to
be set up, called for £70m ($98m) to be spent globally over
10 years on technology to track approaching asteroids.
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