Wild flights of fantasy on the final frontier

It is an index of our fascination with the possibility that we are not alone in the universe that the discovery of the fossil of a single- cell organism that may have lived and died on Mars several million years ago is the stuff of front-page splashes.

If that's the company we've got through all eternity, one is entitled to say, it's a pretty minor mitigation of our loneliness. But it will ensure that the search for larger, perhaps more companionable life forms, will be carried on more avidly than before.

Why does it matter so much? Why is it that practically all of us, however sceptical or consciously indifferent, experience a flutter of excitement at the thought of extraterrestrial life?

It is over 100 years since three men in New Mexico watched aghast as a cigar-shaped craft hovered above them, while the 10 occupants laughed and shouted incomprehensibly, then threw several objects overboard - a flower, a piece of paper with oriental-type writing on it, a curious cup - before flying away. The objects, as happens with tedious regularity in such cases, were later removed by a mysterious stranger. But a modern obsession had been born.

In 1898, HG Wells published The War of the Worlds; eight years later the American astronomer Percival Lowell published his theory that the surface of Mars was veined with canals which the Martians had constructed to irrigate their planet with water from the polar ice-caps. The parallel projects, the literary and the scientific, were off the starting blocks.

It was exactly the sort of imaginative adventure that the 20th century required. In humanity's infancy, heaven lay all about us: what we knew was so infinitesimal, what we could only dream about so vast, that the imagination was abundantly nourished. Above were angels and archangels and all the company of heaven; across the sea beyond Finisterre and ultima Thule were lands unknown, full of inconceivable creatures and men with heads below their shoulders. When night fell, the dark was populated by ghosts. Even in a universe governed by the God of the Christians, there was plenty of room for enjoyably alarming speculation.

With the maturing of knowledge in the 18th and 19th centuries, however, shades of the prison door fell across humanity's dreaming. There is a paradox here: the more breath- taking the discoveries and theories of the intellectual pioneers, the more arid, in consequence, grew the landscape of the popular imagination.

Humanity evolved from the apes, and the rest of "creation" came about in the same way? Bang went God, and the angels and archangels with Him. Character was formed through sexual experiences in infancy? That put paid to the soul, and doubtless to ghosts as well. History was a process of endless struggle between social classes? So much for the great heroes, the supermen of history.

Meanwhile, modern navigation and transport ensured that no significant stone on the planet was left unturned, no nation or tribe undiscovered or undocumented. There was very little left to dream about.

But just when it seemed that things had got about as factual and mechanical and circumscribed as they possibly could, the human mind executed an amazing double somersault, and with one leap it was free. God may be dead, and the Earth as good as, but with the advent of manned flight, suddenly there was a vast new frontier to dream about.

There seems no reason to suppose that our fondness for dreaming about outer space and encountering its denizens will slacken now that a grain of truth has apparently been discovered in all the speculation: like the grit in an oyster, it can only encourage them.

Likewise, it is unlikely to shake the religious belief of those whose faith has survived the assaults of science. In any case, belief in God and in aliens seems to co-exist quite easily: a majority of Americans, for example, believes firmly in both.