'Undoubtedly. Now we know what Zagadka was up to.'

'How did it do the trick? If you were given the contract, Vasili, how would you ignite Jupiter?'

Vasili thought for a minute, then shrugged wryly. 'I'm only a theoretical astronomer – I don't have much experience in this line of business. But let's see... Well, if I'm not allowed to add about ten Jupiter masses, or change the gravitational constant, I suppose I'll have to make the planet denser – hmm, that's an idea...'

His voice trailed off into silence; everyone waited patiently, eyes flickering from time to time to the viewing screens.

The star that had been Jupiter seemed to have settled down after its explosive birth; it was now a dazzling point of light, almost equal to the real Sun in apparent brilliance.

'I'm just thinking out loud – but it might be done this way. Jupiter is – was – mostly hydrogen. If a large percentage could be converted into much denser material – who knows, even neutron matter? – that would drop down to the core. Maybe that's what the billions of Zagadkas were doing with all the gas they were sucking in. Nucleosynthesis – building up higher elements from pure hydrogen. That would be a trick worth knowing! No more shortage of any metal – gold as cheap as aluminium!'

'But how would that explain what happened?' asked Tanya.

'When the core became dense enough, Jupiter would collapse – probably in a matter of seconds. The temperature would rise high enough to start fusion. Oh, I can see a dozen objections – how would they get past the iron minimum; what about radiative transfer; Chandrasekhar's limit. Never mind. This theory will do to start with; I'll work out the details later. Or I'll think of a better one.'

'I'm sure you will, Vasili,' Floyd agreed. 'But there's a more important question. Why did they do it?'

'A warning?' ventured Katerina over the ship's intercom.

'Against what?'

'We'll find that out later.'

'I don't suppose,' said Zenia diffidently, 'that it was an accident?'

That brought the discussion to a dead halt for several seconds.

'What a terrifying idea!' said Floyd. 'But I think we can rule it out. If that was the case, there'd have been no warn – Perhaps. If you start a forest fire because you've been careless, at least you do your best to warn everyone.'

'And there's another thing we'll probably never know,' lamented Vasili. 'I always hoped Carl Sagan would be right, and there'd be life on Jupiter.'

'Our probes never saw any.'

'What chance did they have? Would you find any life on Earth, if you looked at a few hectares of the Sahara or the Antarctic? That's about all we ever did on Jupiter.'

'Hey!' said Brailovsky. 'What about Discovery – and Hal?' Sasha switched on the long-range receiver and started to search on the beacon frequency. There was no trace of a signal.

After a while, he announced to the silently waiting group:

'Discovery's gone.'

No one looked at Dr Chandra; but there were a few muted words of sympathy, as if in consolation to a father who had just lost a son.

But Hal had one last surprise for them.

53 – A Gift of Worlds

The radio message beamed to Earth must have left Discovery only minutes before the blast of radiation engulfed the ship. It was in plain text and merely repeated over and over again:

ALL THESE WORLDS ARE YOURS – EXCEPT EUROPA.

ATTEMPT NO LANDINGS THERE.

There were about a hundred repetitions; then the letters became garbled, and the transmission ceased.

'I begin to understand,' said Floyd, when the message had been relayed by an awed and anxious Mission Control.

'That's quite a parting present – a new sun, and the planets around it.'

'But why only three?' asked Tanya.

'Let's not be greedy,' Floyd replied. 'I can think of one very good reason. We know there's life on Europa. Bowman – or his friends, whoever they may be – want us to leave it alone.'

'That makes good sense in another way,' said Vasili. 'I've been doing some calculations. Assuming that Sol 2 has settled down and will continue to radiate at its present level, Europa should have a nice tropical climate – when the ice has melted. Which it's doing pretty quickly right now.'

'What about the other moons?'

'Ganymede will be quite pleasant – the dayside will be temperate. Callisto will be very cold; though if there's much outgassing, the new atmosphere may make it habitable. But Io will be even worse than it is now, I expect.'

'No great loss. It was hell even before this happened.'

'Don't write off Io,' said Curnow. 'I know a lot of Texarab oilmen who'd love to tackle it, just on general principles. There must be something valuable, in a place as nasty as that. And by the way, I've just had a rather disturbing thought.'

'Anything that disturbs you must be serious,' said Vasili. 'What is it?'

'Why did Hal send that message to Earth, and not to us? We were much closer.'

There was a rather long silence; then Floyd said thoughtfully: 'I see what you mean. Perhaps he wanted to make certain it was received on Earth.'

'But he knew we would relay it – oh!' Tanya's eyes widened, as if she had just become aware of something unpleasant.

'You've lost me,' complained Vasili.

'I think this is what Walter's driving at,' said Floyd. 'It's all very well to feel grateful to Bowman – or whatever gave that warning. But that's all they did. We could still have been killed.'

'But we weren't,' answered Tanya. 'We saved ourselves – by our own efforts. And perhaps that was the whole idea. If we hadn't – we wouldn't have been worth saving. You know, survival of the fittest. Darwinian selection. Eliminating the genes for stupidity.'

'I've an unpleasant feeling you're right,' said Curnow. 'And if we'd stuck to our launch date, and not used Discovery as a booster, would it, or they, have done anything to save us? That wouldn't have required much extra effort for an intelligence that could blow up Jupiter.'

There was an uneasy silence, broken at last by Heywood Floyd.

'On the whole,' he said, 'I'm very glad that's one question we'll never get answered.'

54 – Between Suns

The Russians, thought Floyd, are going to miss Walter's songs and wisecracks on the way home. After the excitement of the last few days, the long fall Sunward – and Earthward – will seem a monotonous anticlimax. But a monotonous, uneventful trip was what everyone devoutly hoped for.

He was already feeling sleepy, but was still aware of his surroundings and capable of reacting to them. Will I look as dead when I'm in hibernation? he asked himself. It was always disconcerting to look at another person – especially someone very familiar – when he had entered the long sleep.

Perhaps it was too poignant a reminder of one's own mortality.

Curnow was completely out, but Chandra was still awake, though already groggy from the final injection. He was obviously no longer himself, for he seemed quite unperturbed by his own nakedness or Katerina's watchful presence. The gold lingam that was his only article of clothing kept trying to float away from him, until its chain recaptured it.

'Everything going okay, Katerina?' asked Floyd.

'Perfectly. But how I envy you. In twenty minutes, you'll be home.'

'If that's any consolation – how can you be sure we won't have some horrible dreams?'

'No one's ever reported any.'

'Ah – they may forget them when they wake up.'

Katerina, as usual, took him quite seriously. 'Impossible. If there were dreams in hibernation, the EEG records would have revealed them. Okay, Chandra – close your eyes. Ah – there he goes. Now it's your turn, Heywood. The ship will seem very strange without you.'