SINCE the beginning of modern times it has been known that the Earth is subjected to a rain of cosmic debris.
Nearly all of it is fine dust or objects that mostly burn up in the atmosphere and are of little consequence to our environment. Occasionally, larger objects survive, can be found on the ground and are known as meteorites.
Sometimes a meteorite causes damage, penetrates a roof or strikes a car, but such events are newsworthy only because of their unusual nature.
What is disturbing about this rain of cosmic debris is that this material has no size cut-off, and unlike terrestrial hazards the implications of a collision with a large object from space may have extreme consequences for our planet. Very rarely an asteroid more than a mile in diameter strikes the earth with serious global consequences that could well threaten the future of civilisation.
More rarely, a cosmic projectile five-to-10 miles across strikes with consequences so terrible that most species are threatened with extinction. It is plausible that a larger object, perhaps 25 miles across or larger, will strike the Earth during our sun’s lifetime which could virtually sterilise the planet.
This discovery has recently generated a programme called Spacewatch which attempts to give prior warning of any asteroid or comet that could come within striking distance of the Earth. The destruction envisioned by an impact of such an object has brought a new undertone to the word Armageddon.
This cosmic catastrophe is bigger than biblical proportions and differs from all other natural hazards in that the potential consequences of a major impact exceed any other known natural or man-made hazard (including nuclear war).
The probability of a major impact occurring in a politically relevant timescale (say, during our lifetimes) is extremely low, but not outside the bounds of possibility.
The impact hazard is, therefore, a terrifying prospect that remains the ultimate high-consequence, low-probability hazard. Predicting Armageddon is more than producing an array of facts and figures, but involves concerns relating to recent impacts.
The first impact of note was in Siberia in June 1908, at a place known as Tunguska; the second was in Brazil in 1930. Thankfully, both areas are depopulated and not a single human was killed, but the consequences could have been very different if these impactors had demolished a city or town. In 1966 an object exploded in an airburst over the frozen Canadian north with a destructive force of 25 kilotons but caused no damage on the ground.
In 1992 a similar incident occurred in the south Pacific with an airburst measuring 30 kilotons.
Now that the threat is out in the open, greater attention is being paid to astronomical projects which seek these threats from space, and alongside them, more balanced views of startling media reports such as the one proclaiming a forthcoming “near-miss” of Earth by a mile-wide asteroid which generated front-page news recently.
Astronomers dare not appear to be like “the boy who cried wolf” by playing on fears whenever an object passes close-by. To do so would mean a loss of credibility when they might someday have to forecast a real threat.
What could be done about it?
We could attempt to deflect the object from its interception with the Earth. This could be done with a high yield nuclear weapon, or deploy a solar sail on the surface of such a body.
This may move the object from its course if the systems were delivered in plenty of time but at present, there exists no rocket capable of lifting them into deep space, and one is unlikely to be developed soon due to the cost factor in the face of such a low risk event.
The alternative approach to this threat would involve destroying the object completely. Depending on the object’s size, several warheads may be able to accomplish this goal. The problem of delivery has yet to be overcome, and few scientists are worried enough to provide solutions.
In addition, some see the nuclear problem as a bigger threat than destruction by natural means, as the possibility of nuclear accidents or deliberate misuse loom over mankind in the short term. However, would the costs of self-preservation be too much to ask?
Astronomers downplay the threat of such events. We have a one in 20,000 chance of such an impact happening within our lifetime, and as our technological capability to deal with such threats grows, so do our chances of avoiding this kind of apocalypse.
The current debate about protecting the Earth from such impacts is just the latest chapter in the long history of our planet.
In short, the most sensible thing to do about these potentially destructive asteroids is try not to think about them.
* Martin Griffiths is a senior lecturer in Astronomy at the University of Glamorgan