'Hello, Dave. What has happened? Where am I?'

He had not known that he could relax, and enjoy a moment of successful achievement. Often before, he had felt like a pet dog controlled by a master whose motives were not wholly inscrutable and whose behaviour could sometimes be modified according to his own desires. He had asked for a bone; it had been tossed to him.

'I will explain later, Hal. We have plenty of time.'

They waited until the last fragments of the ship had dispersed, beyond even their powers of detection. Then they left, to watch the new dawn at the place that had been prepared for them; and to wait through the centuries until they were summoned once again.

It is not true that astronomical events always require astronomical periods of time. The final collapse of a star before the fragments rebound in a supernova explosion can take only a second; by comparison, the metamorphosis of Jupiter was almost a leisurely affair.

Even so, it was several minutes before Sasha was able to believe his eyes. He had been making a routine telescopic examination of the planet – as if any observation could now be called routine! – when it started to drift out of the field of view. For a moment, he thought that the instrument's stabilization was faulty; then he realized, with a shock that jolted his entire concept of the universe, that Jupiter itself was moving, not the telescope. The evidence stared him in the face; he could also see two of the smaller moons – and they were quite motionless.

He switched to a lower magnification, so that he could see the entire disk of the planet, now a leprous, mottled grey. After a few more minutes of incredulity, he saw what was really happening; but he could still scarcely believe it.

Jupiter was not moving from its immemorial orbit, but it was doing something almost as impossible. It was shrinking – so swiftly that its edge was creeping across the field even as he focused upon it. At the same time the planet was brightening, from its dull grey to a pearly white. Surely, it was more brilliant than it had ever been in the long years that Man had observed it; the reflected light of the Sun could not possibly – At that moment, Sasha suddenly realized what was happening, though not why, and sounded the general alarm.

When Floyd reached the observation lounge, less than thirty seconds later, his first impression was of the blinding glare pouring through the windows, painting ovals of light on the walls. They were so dazzling that he had to avert his eyes; not even the Sun could produce such brilliance.

Floyd was so astonished that for a moment he did not associate the glare with Jupiter; the first thought that flashed through his mind was: Supernova! He dismissed that explanation almost as soon as it occurred to him; even the Sun's next-door neighbour, Alpha Centauri, could not have matched the awesome display in any conceivable explosion

The light suddenly dimmed; Sasha had operated the external sun shields. Now it was possible to look directly at the source, and to see that it was a mere pinpoint – just another star, showing no dimensions at all. This could have nothing to do with Jupiter; when Floyd had looked at the planet only a few minutes ago, it had been four times larger than the distant, shrunken sun.

It was well that Sasha had lowered the shields. A moment later, that tiny star exploded – so that even through the dark filters it was impossible to watch with the naked eye. But the final orgasm of light lasted only a brief fraction of a second; then Jupiter – or what had been Jupiter – was expanding once again.

It continued to expand, until it was far larger than it had been before the transformation. Soon the sphere of light was fading rapidly, down to merely solar brilliance; and presently Floyd could see that it was actually a hollow shell, for the central star was still clearly visible at its heart.

He did a quick mental calculation. The ship was more than one light-minute from Jupiter, yet that expanding shell – now turning into a bright-edged ring – already covered a quarter of the sky. That meant it was coming toward them at – My God! – nearly half the speed of light. Within minutes, it would engulf the ship.

Until then, no one had spoken a word since Sasha's first announcement. Some dangers are so spectacular and so much beyond normal experience that the mind refuses to accept them as real, and watches the approach of doom without any sense of apprehension. The man who looks at the onrushing tidal wave, the descending avalanche, or the spinning funnel of the tornado, yet makes no attempt to flee, is not necessarily paralysed with fright or resigned to an unavoidable fate. He may simply be unable to believe that the message of his eyes concerns him personally. It is all happening to somebody else.

As might have been expected, Tanya was the first to break the spell, with a series of orders that brought Vasili and Floyd hurrying to the bridge.

'What do we do now?' she asked, when they had assembled.

We certainly can't run away, thought Floyd. But perhaps we can improve the odds.

'The'ship's broadside on,' he said. 'Shouldn't we turn away from that thing so we're a smaller target? And get as much of our mass as we can between it and us, to act as a radiation shield?'

Vasili's fingers were already flying over the controls.

'You're right, Woody – though it's already too late as far as any gammas and X rays are concerned. But there may be slower neutrons and alphas and heaven knows what else still on the way.'

The patterns of light began to slide down the walls as the ship turned ponderously on its axis. Presently they vanished completely; Leonov was now oriented so that virtually all its mass lay between the fragile human cargo and the approaching shell of radiation.

Will we actually feel the shock wave, wondered Floyd, or will the expanding gases be too tenuous to have any physical effect by the time they reach us? Seen from the external cameras, the ring of fire now almost encircled the sky. But it was fading rapidly; some of the brighter stars could even be seen shining through it. We're going to live, thought Floyd. We've witnessed the destruction of the greatest of planets – and we've survived.

And presently the cameras showed nothing except stars – even if one was a million times brighter than all the others. The bubble of fire blown by Jupiter had swept harmlessly past them, impressive though it had been. At their distance from the source, only the ship's instruments had recorded its passing.

Slowly, the tension aboard relaxed. As always happens in such circumstances, people started to laugh and to make silly jokes. Floyd scarcely heard them; despite his relief at still being alive, he felt a sense of sadness.

Something great and wonderful had been destroyed. Jupiter, with all its beauty and grandeur and now never-to-be-solved mysteries, had ceased to exist. The father of all the gods had been struck down in his prime.

Yet there was another way of looking at the situation. They had lost Jupiter: What had they gained in its place?

Tanya, judging her moment nicely, rapped for attention.

'Vasili – any damage?'

'Nothing serious – one camera burned out. All radiation meters still well above normal, but none near danger limits.'

'Katerina – check the total dosage we've received. It looks as if we were lucky, unless there are more surprises. We certainly owe a vote of thanks to Bowman – and to you, Heywood. Do you have any idea what happened?'

'Only that Jupiter's turned into a sun.'

'I always thought it was much too small for that. Didn't someone once call Jupiter "the sun that failed"?'

'That's true,' said Vasili, 'Jupiter is too small for fusion to start – unaided.'

'You mean, we've just seen an example of astronomical engineering?'