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Big blasts or tiny tugs: how to stop an 
asteroid catastrophe
Great danger of a crash with Earth, but scientists 
are meeting to find a solution.
Alok Jha, science correspondent
March 7, 2007
(Some words are written in italics and marked
like this*. At the end of the article there are some
footnotes to explain what they mean.)
An enormous asteroid flies in from outer space to 
destroy the Earth, an unstoppable force of nature
that we cannot escape. Perhaps a disaster like
this killed off the dinosaurs, and most experts
think the same thing could soon happen to us.
But perhaps there is still hope. Hundreds of
scientists, from nuclear weapons engineers to
planetary experts, are coming to Washington this
week to try to develop a master plan to protect
the Earth from such an asteroid.
The Planetary Defence Conference, organized
by the US Aerospace Corporation, will discuss
lots of ideas on how to develop technology to find 
and redirect objects coming towards the Earth.
The conference will also discuss when and how
to warn people, if the worst comes to the worst.
Many smaller objects flying around the Earth 
in space break up when they reach the
atmosphere, and this is no more dangerous
than a short fireworks display. But there are also 
large asteroids or comets, also called near-Earth
objects* (NEOs). A NEO wider than 1km crashes
into the Earth every few hundred thousand years.
An NEO larger than 6km, which could cause total
extinction, will crash into the Earth every 100
million years. Experts agree that we can expect a
big one soon.
In 2004, scientists discovered a 390-metre wide
asteroid named Apophis. This has an outside
chance* of hitting the Earth in 2036. If it hit,
Apophis would release more than 100,000 times
the energy released in the Hiroshima nuclear
bomb. This blast would directly affect thousands
of square kilometres, but the dust released into
the atmosphere would affect the whole planet.
There could be dark skies* for a year or more,
destroying crops worldwide.
Dr Barbee, a US space expert, thinks that if it
crashed into the Earth, it would be a disaster.
“Such events have occurred in the past and
will occur again in the future”. But now, for the
first time in known history, we may have the 
technology to stop it happening.
Dr Barbee thinks the answer is nuclear. If a
nuclear weapon hit the edge of the asteroid, it
could cause the NEO to change direction, and
not crash into the Earth. The advantage of this
idea is that it is possible with current technology
- though no one has actually tried it yet.
Piet Hut, another expert, has a less dangerous
idea - a robotic tugboat that scientists could
connect to an asteroid and push it out of the
Earth’s path. Modern technology would warn
scientists 10 years in advance, so they could
send the tugboat into position in good time.
The tugboat would use a special engine that
works with electricity instead of fuel. Professor
Hut calculates that such an engine could redirect
NEOs up to 800 metres across.
These engines would also be necessary for
another idea, the “gravity tractor”. But Instead
of landing on an asteroid, the gravity tractor
would hover near it, using the slight gravitational
attraction* between it and the NEO to change its
path.
Psychologists will attend the Washington meeting
as well as technologists. They will discuss how
the public would react psychologically to news of
a possible crash. Al Harrison, an important US
social psychologist, says governments would
worry about how soon to tell people, as they
would not want to frighten everyone.