Possible Asteroid Impact with Earth in 2036
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It's called Apophis. It's 390m wide. And it could hit
Earth in 31 years time
· Scientists call for plans to change asteroid's
path
· Developing technology could take decades
Alok Jha
Wednesday December 7, 2005
Source :
The Guardian
Archived for future reference.
In Egyptian myth, Apophis was the ancient spirit of evil and destruction,
a demon that was determined to plunge the world into eternal darkness.
A fitting name, astronomers reasoned, for a menace now hurtling towards
Earth from outerspace. Scientists are monitoring the progress of a 390-metre
wide asteroid discovered last year that is potentially on a collision course
with the planet, and are imploring governments to decide on a strategy
for dealing with it
Nasa has estimated that an impact from Apophis, which has an outside
chance of hitting the Earth in 2036, would release more than 100,000 times
the energy released in the nuclear blast over Hiroshima. Thousands of square
kilometres would be directly affected by the blast but the whole of the
Earth would see the effects of the dust released into the atmosphere.
And, scientists insist, there is actually very little time left to decide.
At a recent meeting of experts in near-Earth objects (NEOs) in London,
scientists said it could take decades to design, test and build the required
technology to deflect the asteroid. Monica Grady, an expert in meteorites
at the Open University, said: "It's a question of when, not if, a near
Earth object collides with Earth. Many of the smaller objects break up when
they reach the Earth's atmosphere and have no impact. However, a NEO larger
than 1km [wide] will collide with Earth every few hundred thousand years
and a NEO larger than 6km, which could cause mass extinction, will collide
with Earth every hundred million years. We are overdue for a big one."
Apophis had been intermittently tracked since its discovery in June last
year but, in December, it started causing serious concern. Projecting the
orbit of the asteroid into the future, astronomers had calculated that
the odds of it hitting the Earth in 2029 were alarming. As more observations
came in, the odds got higher.
Having more than 20 years warning of potential impact might seem plenty
of time. But, at last week's meeting, Andrea Carusi, president of the Spaceguard
Foundation, said that the time for governments to make decisions on what
to do was now, to give scientists time to prepare mitigation missions. At
the peak of concern, Apophis asteroid was placed at four out of 10 on the
Torino scale - a measure of the threat posed by an NEO where 10 is a certain
collision which could cause a global catastrophe. This was the highest of
any asteroid in recorded history and it had a 1 in 37 chance of hitting
the Earth. The threat of a collision in 2029 was eventually ruled out at
the end of last year.
Alan Fitzsimmons, an astronomer from Queen's University Belfast, said:
"When it does pass close to us on April 13 2029, the Earth will deflect
it and change its orbit. There's a small possibility that if it passes through
a particular point in space, the so-called keyhole, ... the Earth's gravity
will change things so that when it comes back around again in 2036, it will
collide with us." The chance of Apophis passing through the keyhole, a 600-metre
patch of space, is 1 in 5,500 based on current information.
There are no shortage of ideas on how to deflect asteroids. The Advanced
Concepts Team at the European Space Agency have led the effort in designing
a range of satellites and rockets to nudge asteroids on a collision course
for Earth into a different orbit.
No technology has been left unconsidered, even potentially dangerous
ideas such as nuclear powered spacecraft. "The advantage of nuclear propulsion
is a lot of power," said Prof Fitzsimmons. "The negative thing is that ...
we haven't done it yet. Whereas with solar electric propulsion, there are
several spacecraft now that do use this technology so we're fairly confident
it would work."
The favoured method is also potentially the easiest - throwing a spacecraft
at an asteroid to change its direction. Esa plans to test this idea with
its Don Quixote mission, where two satellites will be sent to an asteroid.
One of them, Hidalgo, will collide with the asteroid at high speed while
the other, Sancho, will measure the change in the object's orbit. Decisions
on the actual design of these probes will be made in the coming months, with
launch expected some time in the next decade. One idea that seems to have
no support from astronomers is the use of explosives.
Prof Fitzsimmons. "If you explode too close to impact, perhaps you'll
get hit by several fragments rather than one, so you spread out the area
of damage."
In September, scientists at Strathclyde and Glasgow universities began
computer simulations to work out the feasibility of changing the directions
of asteroids on a collision course for Earth. In spring next year, there
will be another opportunity for radar observations of Apophis that will
help astronomers work out possible future orbits of the asteroid more accurately.
If, at that stage, they cannot rule out an impact with Earth in 2036,
the next chance to make better observations will not be until 2013. Nasa
has argued that a final decision on what to do about Apophis will have to
be made at that stage.
"It may be a decision in 2013 whether or not to go ahead with a full-blown
mitigation mission, but we need to start planning it before 2013," said
Prof Fitzsimmons. In 2029, astronomers will know for sure if Apophis will
pose a threat in 2036. If the worst-case scenarios turn out to be true and
the Earth is not prepared, it will be too late. "If we wait until 2029,
it would seem unlikely that you'd be able to do anything about 2036," said
Mr Yates.
http://www.guardian.co.uk/space/article/0,14493,1660485,00.html
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