ÁñÁ«ÊÓƵ

Intelligence was once defined to me as accurate imagination. Not everyone, perhaps, will accept so simple a definition, but if it were to be used as measure of the achievements of Arthur C. Clarke he would surely rank as prodigiously intelligent.

The idea behind Clarke's latest book, aided by the "accurate imagination" of John Hinkley's Vistapro and Mars Explorer computer programmes, is that one day we may be able to make the apparently sterile planet Mars habitable by life forms including ourselves. Unmanned probes have shown that Mars seems never to have supported life in any form, but though its atmosphere is thin and has very little oxygen, water, so essential to life, has been present there in large quantities. Indeed, Clarke tells us that "there are dried-up river beds that give clear indication of recent flash floods, the first evidence ever found for running water outside our Earth."

But what has become of it, and why have those torrents ceased? The water is thought to be all locked up in polar icecaps and in permafrost, but we know almost nothing of what happened to bring about such a calamity. "I'm afraid I have no ideas ... imagine the same things that caused the earth's ice ages," Clarke once wrote to me.

Here he addresses himself to "terraforming" the chilly, inhospitable planet. The combination of the computer and the author's brilliant interpretations is an outstanding success. The book consists largely of images formed by the computer programmes, interspersed with imaginative paintings by "space artists" (Clarke's phrase), showing stages in the terraforming process, the first lichens giving way to more advanced vegetation, pines supplanted by oaks and similar broad-leaved trees with the oxygen content of the atmosphere increasing substantially in the process, as it did on earth in past millennia as a result of oxygen generated and released by green plants.

The computer image shown here is of the caldera of the extinct volcano Olympus Mons, by far the largest mountain in the solar system, as it might appear in the year ad 4,000 (for terraforming will certainly take as long as that, according to the author). Blue skies have replaced the present Martian pink, caused by red dust; there are tranquil lakes and verdant slopes; the only clue that this is an extraterrestrial image are the sharp-edged cliffs lacking in the erosion that would inevitably occur on earth.

Those who come after us in the approaching century may well regard The Snows of Olympus as being among the author's finest achievements. It is worth reminding ourselves, and particularly those of us inclined to scepticism, that October marks the 50th anniversary of Arthur C. Clarke's paper in Wireless World in which he described, complete with the necessary mathematics, how geosynchronous satellites could be put in orbit around our own planet. He was ignored in 1945. In 1995 we could not do without them.

Harry Miller, award-winning photographer and fellow of the Zoological Society, accompanied Arthur C. Clarke during his observation of a total solar eclipse in 1980.