by
Sir Arthur C Clarke, Kt., CBE
Chancellor, University of Moratuwa, Sri Lanka
26 May 1998
Less than four years ago, in October 1994, I devoted my Convocation Address to something which probably few people had ever worried about - the danger to our planet of impacts from space. Well, during those four years so much has happened that I make no apologies for returning to the subject.
If you spend a few hours at night under a perfectly clear sky - which, alas, I haven't done for years - you are almost certain to see a few meteors sliding silently across the stars; there are times, indeed, when you may see hundreds. One such occasion is due in November 1999: a Space Shuttle launch has been rescheduled, and the owners of communications satellites are already rushing to take out insurance. For though that 'shining furrow', as Tennyson called it, is caused by an object not much larger than a pea burning up as it enters the atmosphere, that has enough energy to damage, or even destroy, delicate orbiting equipment costing hundreds of millions of dollars. Tennyson, who a century and a half ago saw 'the heavens filled with commerce' could never have imagined that one day this would be literally true.
Quite often, one of these cosmic fragments is large enough to survive passage through the atmosphere, and falls to earth. We then call it a 'meteorite'; the word 'meteor' applies merely to the streak of light across the sky.
That meteorites did fall - sometimes in large numbers over considerable areas - had been known from time immemorial; indeed, it has been suggested that they were the only source of iron for early man. Yet two hundred years ago, in what has been called the Age of Enlightenment, there was great scepticism about their existence. Thomas Jefferson, widely considered the most brilliant President ever to sit in the White House, once remarked after hearing that a couple of academic gentlemen had witnessed a shower of meteorites: "I would rather believe that two Yankee professors lied, than that stones fell from the sky." Well, now we know that mountains can fall from the sky.
The evidence is overwhelming, yet only in the last few decades has this been accepted: as someone once said: "The obvious we see eventually."
Perhaps the best example of this phenomenon is the famous Meteor Crater in Arizona - a huge hole in the ground more than a kilometre across. Despite the perfectly accurate name that the locals had given to it, for years most geologists argued that the crater was home-grown - some kind of volcanic formation! Now we know that it was produced by the impact some 50,000 years ago of a nickel-iron mass about as large as this building. Once they removed their mental blindfolds, geologists started finding impact craters all over the world. About two hundred have now been identified, and there must be many more hidden in the ocean depths. We live in a very dangerous neighborhood: what has happened countless times in the past will, inevitably, occur again in the future.
What did most to focus the attention of the scientific - and non-scientific - community on this fact was a paper published in 1980 by the American physicist Luis Alvarez and his geologist son Walter, suggesting that the extinction of the dinosaurs was linked with the impact of an asteroid on Earth, about 65 million years ago*.
* Luis was a good friend of mine, and I dedicated my 1963 novel Glide Path to him. This work of barely disguised fiction was based on my experiences as an RAF officer when I took over the GCA (Ground Control Approach) radar blind-landing system which 'Luie' had invented at the Massachusetts Institute of Technology. The main protagonist was modelled on him, and I am very happy that my prediction of his Nobel Prize came true a few years later.
The word 'asteroid' is unfortunate, because it means 'small star' - and asteroids are in fact only small planets, most of them between Mars and Jupiter. The largest, Ceres, is just under a thousand kilometres across, but they come in all sizes down to ones that would sit comfortably on the Galle Face Green (what there is left of it.) So where one draws the line between meteorites and asteroids is a matter of definition; they all bits of debris left over from the formation of the Solar System.
And so are comets, which are enormously larger but no heavier than asteroids, since they are almost entirely clouds of extremely thin gas, surrounding a small, solid nucleus. When, after many trips round the sun, all its volatile material has boiled off into space, only this core is left - and the comet becomes a normal asteroid.
I am proud to say that the International Astronomical Union, which is in charge of such matters, recently named an asteroid (previously known only by a number, 4923) after me. It's about ten kilometres in diameter, and spends most of its time near the orbit of Mars, so I'm afraid its climate is rather chilly. The IAU apologised to me because Number 2001 was no longer available. Apparently it had been allocated several years ago, to somebody named A. Einstein.
As far as the resulting damage to planet Earth was concerned, it would not make the slightest difference whether the impactor was a comet or an asteroid. However, because it is such an impressive astronomical object, we could see a comet months before it hit. But an asteroid might give only two minute's warning, when the sky suddenly exploded...
This happened over a remote part of Siberia in 1908. Luckily, though a huge area of forest was devastated, there was no loss of human life.
There have been several other major events since then, again in uninhabited areas, and in 1972 there was a hair-raising near-miss. On 10 August, a large meteorite streaked half way across the United States and was seen not only by thousands of people, but recorded by many amateur photographers. It came within a mere 58 kilometres of ground level; had its trajectory been slightly different, some American city might have emulated Hiroshima.
I'm not sure if this provided any inspiration for my novel Rendezous with Rama, which opened with the destruction of Northern Italy by asteroid impact in the year 2077. This disaster resulted in the establishment of a warning system, to which I gave the name - SPACEGUARD. Well, fact has followed fiction. When the U.S. House of Representatives asked NASA to study the problem, I was delighted when the resulting 1992 report was entitled THE SPACEGUARD SURVEY, with due acknowledgement.
That same year, a senior editor of TIME wrote to me saying that though the magazine had never deliberately published fiction, they'd like me to write a short story for a special issue. The result was The Hammer of God, in which I attempted to answer the question: what could we do to save ourselves if we see a killer rock headed this way?
The novel-length version of The Hammer of God appeared in 1993 - and just one year later, the whole world had a grandstand view of the most spectacular collision ever observed in our Solar System. The impact of Comet Shoemaker-Levy 9 on Jupiter in July 1994 made holes in the giant planet's atmosphere larger than the Earth; they could be seen even in the smallest telescope, and the after-effects lingered for months.
Only a few weeks ago, there was a great deal of alarm when the initial orbit calculated for the newly-discovered asteroid 1997 XF11 suggested that it might collide with Earth in the year 2028. Luckily, after a hunt through the thousands of photographic plates collected by astronomers over many decades, an earlier image of XF11 was discovered. This made it possible to compute a much more accurate orbit, and we now know that there is no danger from this particular asteroid - at least for millions of years!
This rather embarrassing affair - the correction came only a day after the initial report - has triggered a major debate in the astronomical community. A protocol is now being drawn up to reduce the chance of any premature and perhaps inacurate announcement. And I am happy to say that NASA is now in the process of establishing a new office to deal with the problem, with an initial annual budget of $3,000,000.
Among the members of NASA's SPACEGUARD Committee is my old friend the Dutch-American astronomer Tom Gehrels, one of the world's leading experts on asteroids. He has visited Sri Lanka on several occasions, hoping to establish an observatory here - so far without success, because of a deplorable lack of interest in astronomy (as opposed to astrology!)
This situation, I hope, may be rectified now that the Japanese Government has made an extraordinarily generous gift of a half-million dollar observatory-class telescope, currently located at the Arthur Clarke Centre. Although this is far from being an ideal location, the best observing sites are currently inaccessible and good work can still be done at Moratuwa - if we can find experienced and enthusiastic staff. I might add that most comets and many asteroids are discovered by amateurs working with telescopes considerably smaller than the one we now possess.
Some might argue that, in a world already nervous about global warming, poisoned oceans, DIY nuclear bombs, etc. etc., any discussion of protection from asteroids amd comets is a massive exercise in irrelevancy. Yet there is much that can - and should - be done, as is proved by the current intense debate among astronomers, space scientists, and under-employed Star Warriors looking for new targets.
It is an old idea - going back at least to Andre Maurois' "The War Against The Moon" (1927) - that only a threat from beyond the Earth could unify the quarrelsome human species. So it may indeed be a stroke of luck that such a threat has been discovered, at just the period in history when we can devise technologies to deal with it.
Although some suggested cures may sound worse than the disease (Dr Edward Teller has proposed a bodyguard of orbiting H-bombs) there are several plausible alternatives. They all depend on the length of the warning time available.
Of the many defences proposed, the most elegant (and environmentally friendly!) one is to rendezvous with any asteroid on an orbit liable to impact Earth, and to persuade it to make a slight change of course. If there was sufficient warning time, only a modest amount of rocket propulsion would be necessary. This was the scenario I developed in The Hammer of God, which was later optioned by a promising young movie-maker named Steven Spielberg. I don't know how much of my story he has used, but I have a double interest in Deep Impact, as he is calling the film. The role of the first black President of the United States is played by Morgan Freeman, now considered by many to be the finest actor in America. Well, Morgan has just optioned my own Rendezvous with Rama, which started the whole SPACEGUARD business. I can't wait...
Meanwhile SPACEGUARD Foundations have been set up in the UK, the US and Australia, to persuade goverments to fund a survey which would, for the first time, give us some idea of the real extent of the danger. At the moment, we probably do not know even one tenth of the NEO's - Near Earth Objects - which must exist.
In one of his last books, Carl Sagan pointed out that no really long-lived civilization could survive unless it develops space travel, because major asteroid impacts will be inevitable in any solar system over the course of millennia. Larry Niven summed up the situation with the memorable phrase: "The dinosaurs became extinct because they didn't have a space programme." And we will deserve to become extinct, if we don't have one.
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