Second Officer Chang had been wrestling with the problem ever since Galaxy had been successfully – to his surprise as much as his relief – injected into transfer orbit. For the next couple of hours she was in the hands of God, or at least Sir Isaac Newton; there was nothing to do but wait until the final braking and descent manoeuvre.

He had briefly considered trying to fool Rosie by giving the ship a reverse vector at closest approach, and so taking it out into space again. It would then be back in a stable orbit, and a rescue could eventually be mounted from Ganymede. But there was a fundamental objection to this scheme: he would certainly not be alive to be rescued. Though Chang was no coward, he would prefer not to become a posthumous hero of the spaceways.

In any event, his chances of surviving the next hour seemed remote. He had been ordered to take down, single-handed, a three-thousand tonner on totally unknown territory. This was not a feat he would care to attempt even on the familiar Moon.

'How many minutes before you start braking?' asked Rosie. Perhaps it was more of an order than a question; she clearly understood the fundamentals of astronautics, and Chang abandoned his last wild fantasies of outwitting her.

'Five,' he said reluctantly. 'Can I warn the rest of the ship to stand by?'

'I'll do it. Give me the mike... THIS IS THE BRIDGE. WE START BRAKING IN FIVE MINUTES. REPEAT, FIVE MINUTES. OUT.'

To the scientists and officers assembled in the wardroom, the message was fully expected. They had had one piece of luck; the external video monitors had not been switched off. Perhaps Rose had forgotten about them; it was more likely that she had not bothered. So now, as helpless spectators – quite literally, a captive audience – they could watch their unfolding doom.

The cloudy crescent of Europa now filled the field of the rear-view camera. There was no break anywhere in the solid overcast of water vapour recondensing on its way back to nightside. That was not important, since the landing would be radar-controlled until the last moment. It would, however, prolong the agony of observers who had to rely on visible light,

No-one stared more intently at the approaching world than the man who had studied it with such frustration for almost a decade. Rolf van der Berg, seated in one of the flimsy low-gravity chairs with the restraining belt lightly fastened, barely noticed the first onset of weight as braking commenced.

In five seconds, they were up to full thrust. All the officers were doing rapid calculations on their comsets; without access to Navigation, there would be a lot of guesswork, and Captain Laplace waited for a consensus to emerge.

'Eleven minutes,' he announced presently, 'assuming he doesn't reduce thrust level – he's at max now. And assuming he's going to hover at ten kilometres – just above the overcast – and then go straight down. That could take another five minutes.'

It was unnecessary for him to add that the last second of those five minutes would be the most critical.

Europa seemed determined to keep its secrets to the very end. When Galaxy was hovering motionless, just above the cloudscape, there was still no sign of the land – or sea – beneath. Then, for a few agonizing seconds, the screens became completely blank – except for a glimpse of the now extended, and very seldom used, landing gear. The noise of its emergence a few minutes earlier had caused a brief flurry of alarm among the passengers; now they could only hope that it would perform its duty.

How thick is this damn cloud? van der Berg asked himself. Does it go all the way down -No, it was breaking, thinning out into shreds and wisps – and there was the new Europa, spread out, it seemed, only a few thousand metres below.

It was indeed new; one did not have to be a geologist to see that. Four billion years ago, perhaps, the infant Earth had looked like this, as land and sea prepared to begin their endless conflict.

Here, until fifty years ago, there had been neither land nor sea – only ice. But now the ice had melted on the Lucifer-facing hemisphere, the resulting water had boiled upwards – and been deposited in the permanent deep-freeze of nightside. The removal of billions of tons of liquid from one hemisphere to the other had thus exposed ancient seabeds that had never before known even the pale light of the far-distant Sun.

Some day, perhaps, these contorted landscapes would be softened and tamed by a spreading blanket of vegetation; now they were barren lava flows and gently steaming mud flats, interrupted occasionally by masses of up-thrust rock with strangely slanting strata. This had clearly been an area of great tectonic disturbance, which was hardly surprising if it had seen the recent birth of a mountain the size of Everest.

And there it was – looming up over the unnaturally close horizon. Rolf van der Berg felt a tightness in his chest, and a tingling of the flesh at the back of his neck. No longer through the remote impersonal senses of instruments, but with his own eyes, he was seeing the mountain of his dreams.

As he well knew, it was in the approximate shape of a tetrahedron, tilted so that one face was almost vertical. (That would be a nice challenge to climbers, even in this gravity – especially as they couldn't drive pitons into it...) The summit was hidden in the clouds, and much of the gently-sloping face turned towards them was covered with snow.

'Is that what all the fuss is about?' muttered someone in disgust. 'Looks like a perfectly ordinary mountain to me. I guess that once you've seen one -' He was 'shushed' angrily into silence.

Galaxy was now drifting slowly towards Mount Zeus, as Chang searched for a good landing place. The ship had very little lateral control, as ninety per cent of the main thrust had to be used merely to support it. There was enough propellant to hover for perhaps five minutes; after that, he might still be able to land safely – but he could never take off again.

Neil Armstrong had faced the same dilemma, almost a hundred years ago. But he had not been piloting with a gun aimed at his head.

Yet for the last few minutes, Chang had totally forgotten both gun and Rosie. Every sense was focused on the job ahead; he was virtually part of the great machine he was controlling. The only human emotion left to him was not fear – but exhilaration. This was the job he had been trained to perform; this was the highlight of his professional career – even as it might be the finale.

And that was what it looked like becoming. The foot of the mountain was now less than a kilometre away – and he had still found no landing site. The terrain was incredibly rugged, torn with canyons, littered with gigantic boulders. He had not seen a single horizontal area larger than a tennis court -and the red line on the propellant gauge was only thirty seconds away.

But there, at last, was a smooth surface – much the flattest he'd seen – it was his only chance within the time frame.

Delicately, he juggled the giant, unstable cylinder he was controlling towards the patch of horizontal ground – it seemed to be snow-covered – yes, it was – the blast was blowing the snow away – but what's underneath? – looks like ice – must be a frozen lake – how thick? – HOW THICK? -The five-hundred-ton hammer-blow of Galaxy's main jets hit the treacherously inviting surface. A pattern of radiating lines sped swiftly across it; the ice cracked, and great sheets started to overturn. Concentric waves of boiling water hurtled outwards as the fury of the drive blasted into the suddenly uncovered lake.

Like the well-trained officer he was, Chang reacted automatically, without the fatal hesitations of thought. His left hand ripped open the SAFETY LOCK bar; his right grabbed the red lever it protected – and pulled it to the open position.