astrode (moved from ATSNN)

Electronic Telegraph International News Friday 13 March 1998 Issue 1022
Asteroid may spell doom for human civilisation
By Aisling Irwin, Science Correspondent
AN asteroid capable of destroying civilisation may be on a collision course with Earth, astronomers said yesterday.
The asteroid will pass very close to Earth in 30 years' time. If it hits, the collision will be at 6.30pm GMT on Thursday, Oct 26 2028. However, experts' predictions of the chance of a collision varied widely.
Don Yeomans, of Nasa's Jet Propulsion Laboratory in Pasadena, California, who is viewed by many as the world's leading expert on planetary orbits, said the chance was "zero". Others said it was one in 1,000.
Astronomers agreed, however, that the asteroid, 1997 XF11, is most likely to zoom past at a distance of 30,000 miles - an eighth of the distance to the Moon.
"This is big," said Brian Marsden, of the International Astronomical Union, which announced the discovery of XF11 yesterday. "We have never had experience of anything this big. The chance of an actual collision is small, but one is not entirely out of the question."
Benny Peiser, a specialist in the effects of cosmic debris at Liverpool John Moores University, said: "The effect of a one-mile-wide object hitting the Earth would be catastrophic on a global scale. It would not necessarily lead to the extinction of animals or humans but it would have a tremendous environmental impact."
Dr Peiser, a member of the pressure group Spaceguard UK which wants an international monitoring programme to spot dangerous comets and asteroids, said: "I don't think this asteroid will hit Earth. But a collision with one of that size would wipe out civilisation as we know it. We would regress to the level of the Dark Ages. There could be massive earthquakes produced by the energy yielded by such an impact. If it hit one of the oceans, which is likely, it would trigger tidal waves which would most certainly wipe out the coastal regions in that part of the world. An enormous amount of soil and dust would be sent into the atmosphere which could trigger a cosmic winter lasting a prolonged time.
"Most people would be killed not by the impact itself, but by the knock-on effects. There would be a complete collapse of society and the abandonment of agricultural settlements. It's inevitable that at some point in our history a large object will impact. It's just a question of time."
An asteroid the size of 1997 XF11 colliding with the Earth at more than 17,000mph would explode with the energy of almost two million Hiroshima-sized atomic bombs.
Dr Marsden said that the next five years should be spent establishing definitively whether the asteroid is going to hit Earth. If it is, there will still be 25 years in which to act.
There would be two principal courses of action. We could launch a nuclear bomb timed to explode beside XF11 when it is hundreds of thousands of miles away from Earth. The force of a nuclear explosion would nudge the asteroid just an inch out of its path and this distortion would amplify over the years into a path that would miss Earth with a comfortable margin. One obstacle to this approach is an international treaty banning the use of nuclear weapons in space.
Alternatively, humans could establish a base on the Moon from which to blast the asteroid with a strong laser beam, chipping tiny bits off it and distorting its path.
If XF11 does not hit Earth, and it is a clear night, it will pass over Europe and people will be able to watch it soar from north-west to south-east over a couple of hours.
Astronomers described yesterday how the mile-wide object was first spotted by Jim Scotti, an astronomer in Arizona, on Dec 6. At first, scientists thought that it would pass Earth at a huge distance. Then, over the next 14 days, more observations were made and the calculations yielded narrower and narrower margins between it and Earth. By February, they were predicting a 500,000-mile pass.
A month later, new observations extended the graph of the asteroid's orbit and the margin suddenly shrank to 30,000 miles. "It was amazingly close," said Dr Marsden. "We have had small objects come within under 70 miles of Earth but those were tiny."
The Jet Propulsion Laboratory in Pasadena yesterday confirmed the calculations but predicted a greater gap, of 45,000 miles. The Moon is about 250,000 miles away.
Dr Marsden issued a plea to astronomers to try to catch traces of the asteroid before it fades over the sun's horizon in two months' time, after which there will be no more information about for about 20 months.
In early 2000 it will be visible through moderate-sized telescopes with electronic sensors. On Hallowe'en night in 2002 it will be so near that even modest telescopes will be able to detect it.
The Royal Astronomical Society warned that the 1-in-1,000 chance of a collision was based on uncertainties in our knowledge, not on variations in the asteroid's path. Dr Jacqueline Mitton said: "It is not something that's going to change - either the asteroid is going to hit us or it is not. It is simply that we are looking at limited data."
12 March 1998: Are we sitting ducks in a cosmic shooting gallery?
24 July 1997: Asteroids 'combined to destroy'
27 April 1997: Nasa to launch missiles against asteroids
2 January 1997: Earth watches for asteroids 'running riot'
30 November 1996: Close encounter as chaotic asteroid passes only 3.3m miles from Earth

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