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Christine McGourty reports for BBC News
"Our planet has been struck before"
 real 28k

Dr Harry Atkinson, Near Earth Objects Task Force
"It seems prudent to look at these risks"
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Austin Atkinson
Twenty years notice would be about enough
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Tuesday, 4 January, 2000, 13:39 GMT
Saving the world from asteroids

The Torino scale of asteroid impact The Torino scale of asteroid impact

A gentle push, not a nuclear blast, would be the best way to deal with an asteroid threatening the Earth, according to a member of the UK Government's taskforce which was announced on Tuesday.

I think we are dimly aware that there is a major problem here that we need to understand. We are a long way from tying down the details
Professor David Williams
Although Hollywood heroics involving space acrobatics and nuclear bombs have more dramatic potential, blasting an asteroid which is arrowing in on Earth could be the worst option.

Professor David Williams, of University College London and formerly of Nasa's Space Science Data Centre, told BBC News Online that detonating a rocky object would simply create lots of individual asteroids which could rain down destruction over a larger area.

He said that a better option would be landing a solar-powered engine on the object that would then gently push the asteroid out of its collision course.

"The approach would be trapping sunlight, turning it into electricity to power an ion gun and exerting a very small force on the object, but over a long time. This would just nudge it out of the orbit it is currently in."

Dinosaurs were wiped out by a meteorite Dinosaurs were wiped out by a meteorite
A very small shove on an asteroid whilst it is far away could mean the difference between hitting the Earth and missing it by more than half a million kilometres (300,000 miles), said Professor Williams.

The engine could be created using technology available today. And expertise required to place the engine on the object is being gained from missions to the asteroid Eros and to a comet, by the Rosetta mission.

Two-year warning

Estimates of the likely period of warning of a doomsday asteroid vary from two years to 20.

Austin Atkinson, an author on asteroids, believes that 20 years would be enough time to reach and deflect an object but added: "It is very hard to get a rocket from Earth to reach an object within two years."

The purpose of the taskforce is to assess how the UK can contribute to the global asteroid watch. Mr Atkinson said: "I think everyone is delighted that Lord Sainsbury has set up this taskforce. Let's hope they argue in favour of setting up an observation post in Britain."

Space probes have been sent to investigate asteroids Space probes have been sent to investigate asteroids
Professor Williams added: "The UK is not going to save the world, but will contribute to the co-ordinated worldwide effort in this regard."

Asteroids near Earth travel at between 20 and 30 kilometres per second, making them both hard to intercept and hard to see. International efforts currently centre on watching the orbits of asteroids more closely in order to make more accurate predictions of their future course.

The chances of a serious asteroid strike on Earth are very small but the consequences are so catastrophic that, when averaged out over time, the chances of being killed by a major impact are 1 in 20,000, the same as being killed in an aeroplane crash.

Asteroids bigger than two kilometres (1.25 miles) would quite probably wipe out the human race but are only expected once every million years or so.

However, space objects in the range 50 to 100 metres could kill tens of millions of people if they struck a city.

Nuclear blast

One such object was a 60m-wide comet that exploded over Siberia in 1908 with 600 times the energy of the bomb dropped on Hiroshima. It laid waste to a 40km-wide patch of forest. Events like this are expected every 100 to 300 years.

Dr Matt Genge, from London's Natural History Museum, described what would have happened if the Siberian comet had hit London.

As it plunged downwards, sonic booms would thunder from the sky, just before the comet exploded with tremendous force. Dr Genge said: "You'd get a large shock wave and thermal flash. It's almost exactly the same as a nuclear air burst.

"Let's say you're a very fast thinker. In the microseconds you have left, the first thing is that everything would burst into flames, including you. You'd be knocked off your feet by the shock wave and then dragged back again towards the explosion as all the air rushes back in."

After the blast, London would be a wasteland of flattened, charred buildings and blackened corpses.

The three-man task force will make its recommendations by the middle of 2000.

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See also:
04 Jan 00 |  UK
The end is nigh, again
17 Sep 99 |  Sheffield 99
Small but deadly comets identified
30 Jul 99 |  Sci/Tech
Spacecraft fails to keep eye on job
26 Jul 99 |  Sci/Tech
Exploring century's greatest explosion
23 Jul 99 |  Sci/Tech
Asteroid impact scale endorsed
19 May 99 |  Sci/Tech
Close shave with asteroid
18 Feb 99 |  Sci/Tech
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