Strangest of all, though, was to sit up here on the Rim, in the Geostationary Orbit itself – and to feel weight! Just metres away, outside the window of the tiny observation lounge, servicing robots and a few spacesuited humans were gliding gently about their business; yet here inside Goliath the inertial field was maintaining standard Mars-gee.

'Sure you don't want to change your mind, Frank?' Captain Chandler had asked jokingly, as he left for the bridge. 'Still ten minutes before lift-off.'

'Wouldn't be very popular if I did, would I? No – as they used to say back in the old days – we have commit. Ready or not, here I come.'

Poole felt the need to be alone when the drive went on, and the tiny crew – only four men and three women – respected his wish. Perhaps they guessed how he must be feeling, to leave Earth for the second time in a thousand years – and, once again, to face an unknown destiny.

Jupiter-Lucifer was on the other side of the Sun, and the almost straight line of Goliath's orbit would take them close to Venus. Poole looked forward to seeing, with his own unaided eyes, if Earth's sister planet was now beginning to live up to that description, after centuries of terraforming.

From a thousand kilometres up, Star City looked like a gigantic metal band around Earth's Equator, dotted with gantries, pressure domes, scaffolding holding half-completed ships, antennas, and other more enigmatic structures. It was diminishing swiftly as Goliath headed sunwards, and presently Poole could see how incomplete it was: there were huge gaps spanned only by a spider's web of scaffolding, which would probably never be completely enclosed.

And now they were falling below the plane of the ring; it was midwinter in the northern hemisphere, so the slim halo of Star City was inclined at over twenty degrees to the Sun. Already Poole could see the American and Asian towers, as shining threads stretching outwards and away, beyond the blue haze of the atmosphere.

He was barely conscious of time as Goliath gained speed, moving more swiftly than any comet that had ever fallen sunwards from interstellar space. The Earth, almost full, still spanned his field of view, and he could now see the full length of the Africa Tower which had been his home in the life he was now leaving – perhaps, he could not help thinking, leaving for ever.

When they were fifty thousand kilometres out, he was able to view the whole of Star City, as a narrow ellipse enclosing the Earth. Though the far side was barely visible, as a hair-line of light against the stars, it was awe-inspiring to think that the human race had now set this sign upon the heavens.

Then Poole remembered the rings of Saturn, infinitely more glorious. The astronautical engineers still had a long, long way to go, before they could match the achievements of Nature.

Or, if that was the right word, Deus.

When he woke the next morning, they were already at Venus. But the huge, dazzling crescent of the still cloud-wrapped planet was not the most striking object in the sky:

Goliath was floating above an endless expanse of crinkled silver foil, flashing in the sunlight with ever-changing patterns as the ship drifted across it.

Poole remembered that in his own age there had been an artist who had wrapped whole buildings in plastic sheets: how he would have loved this opportunity to package billions of tons of ice in a glittering envelope... Only in this way could the core of a comet be protected from evaporation on its decades-long journey sunwards.

'You're in luck, Frank,' Chandler had told him. 'This is something I've never seen myself. It should be spectacular. Impact due in just over an hour. We've given it a little nudge, to make sure it comes down in the right place. Don't want anyone to get hurt.'

Poole looked at him in astonishment.

'You mean – there are already people on Venus?'

'About fifty mad scientists, near the South Pole. Of course, they're well dug in, but we should shake them up a bit – even though Ground Zero is on the other side of the planet. Or I should say "Atmosphere Zero" – it will be days before anything except the shockwave gets down to the surface.'

As the cosmic iceberg, sparkling and flashing in its protective envelope, dwindled away towards Venus, Poole was struck with a sudden, poignant memory. The Christmas trees of his childhood had been adorned with just such ornaments, delicate bubbles of coloured glass. And the comparison was not completely ludicrous: for many families on Earth, this was still the right season for gifts, and Goliath was bringing a present beyond price to another world.

The radar image of the tortured Venusian landscape – its weird volcanoes, pancake domes, and narrow, sinuous canyons – dominated the main screen of Goliath's control centre, but Poole preferred the evidence of his own eyes. Although the unbroken sea of clouds that covered the planet revealed nothing of the inferno beneath, he wanted to see what would happen when the stolen comet struck. In a matter of seconds, the myriad of tons of frozen hydrates that had been gathering speed for decades on the downhill run from Neptune would deliver all their energy...

The initial flash was even brighter than he had expected. How strange that a missile made of ice could generate temperatures that must be in the tens of thousands of degrees! Though the filters of the view-port would have absorbed all the dangerous shorter wave-lengths, the fierce blue of the fireball proclaimed that it was hotter than the Sun.

It was cooling rapidly as it expanded – through yellow, orange, red... The shockwave would now be spreading outwards at the velocity of sound – and what a sound that must be! – so in a few minutes there should be some visible indication of its passage across the face of Venus.

And there it was! Only a tiny black ring – like an insignificant puff of smoke, giving no hint of the cyclonic fury that must be blasting its way outwards from the point of impact. As Poole watched, it slowly expanded, though owing to its scale there was no sense of visible movement: he had to wait for a full minute before he could be quite sure that it had grown larger.

After a quarter of an hour, however, it was the most prominent marking on the planet. Though much fainter – a dirty grey, rather than black – the shockwave was now a ragged circle more than a thousand kilometres across. Poole guessed that it had lost its original symmetry while sweeping over the great mountain ranges that lay beneath it.

Captain Chandler's voice sounded briskly over the ship's address system.

'Putting you through to Aphrodite Base. Glad to say they're not shouting for help -'

'– shook us up a bit, but just what we expected. Monitors indicate some rain already over the Nokomis Mountains – it will soon evaporate, but that's a beginning. And there seems to have been a flash-flood in Hecate Chasm – too good to be true, but we're checking. There was a temporary lake of boiling water there after the last delivery -'

I don't envy them, Poole told himself – but I certainly admire them. They prove that the spirit of adventure still exists in this perhaps too-comfortable and too-well-adjusted society.

'– and thanks again for bringing this little load down in the right place. With any luck – and if we can get that sun-screen up into sync orbit – we'll have some permanent seas before long. And then we can plant coral reefs, to make lime and pull the excess CO2 out of the atmosphere – hope I live to see it!'

I hope you do, thought Poole in silent admiration. He had often dived in the tropical seas of Earth, admiring weird and colourful creatures so bizarre that it was hard to believe anything stranger would be found, even on the planets of other suns.