'Six minutes to ignition,' said Hal. 'All systems nominal. I am ready to stop the countdown if you agree. Let me remind you that my prime directive is to study everything in Jupiter space that may be connected with intelligence.'
Floyd recognized that phrase all too well: he had written it himself. He wished he could delete it from Hal's memory.
A moment later, he had reached the bridge and joined the Orlovs. They both looked at him with alarmed concern.
'What do you recommend?' asked Tanya swiftly.
'It's up to Chandra, I'm afraid. Can I speak to him – on the private line?'
Vasili handed over the microphone.
'Chandra? I assume that Hal can't hear this?'
'Correct, Dr Floyd.'
'You've got to talk quickly. Persuade him that the countdown must continue, that we appreciate his – er, scientific enthusiasm – ah, that's the right angle – say we're confident that he can do the job without our help. And we'll be in touch with him all the time, of course.'
'Five minutes to ignition. All systems nominal. I am still waiting for your answer, Dr Chandra.'
So are we all, thought Curnow, only a metre away from the scientist. And if I do have to push that button at last, it will be something of a relief. In fact, I'll rather enjoy it.
'Very well, Hal. Continue the countdown. I have every confidence in your ability to study all phenomena in Jupiter space, without our supervision. Of course, we will be in touch with you at all times.'
'Four minutes to ignition. All systems nominal. Propellant-tank pressurization completed. Voltage steady on plasma trigger. Are you sure you are making the right decision, Dr Chandra? I enjoy working with human beings and have a stimulating relationship with them. Ship's attitude correct to point one milliradian.'
'We enjoy working with you, Hal. And we will still be doing so, even if we are millions of kilometres away.'
'Three minutes to ignition. All systems nominal, Radiation shielding checked. There is a problem of the time lag, Dr Chandra. It may be necessary to consult each other without any delay.'
This is insane, Curnow thought, his hand now never far from the cut-off switch. I really believe that Hal is – lonely. Is he mimicking some part of Chandra's personality that we never suspected?
The lights flickered, so imperceptibly that only someone familiar with every nuance of Discovery's behaviour would have noticed. It could be good news or bad – the plasma firing sequence starting, or being terminated...
He risked a quick glance at Chandra; the little scientist's face was drawn and haggard, and for almost the first time Curnow felt real sympathy for him as another human being. And he remembered the startling information that Floyd had confided in him – Chandra's offer to stay with the ship, and keep Hal company on the three-year voyage home. He had heard no more of the idea, and presumably it had been quietly forgotten after the warning. But perhaps Chandra was being tempted again; if he was, there was nothing that he could do about it at that stage. There would be no time to make the necessary preparations, even if they stayed on for another orbit and delayed their departure beyond the deadline. Which Tanya would certainly not permit after all that had now happened.
'Hal,' whispered Chandra, so quietly that Curnow could scarcely hear him. 'We have to leave. I don't have time to give you all the reasons, but I can assure you it's true.'
'Two minutes to ignition. All systems nominal. Final sequence started. I am sorry that you are unable to stay. Can you give me some of the reasons, in order of importance?'
'Not in two minutes, Hal. Proceed with the countdown. I will explain everything later. We still have more than an hour together.'
Hal did not answer. The silence stretched on and on. Surely the one-minute announcement was overdue ...
Curnow glanced at the clock. My God, he thought, Hal's missed it! Has he stopped the countdown?
Curnow's hand fumbled uncertainly for the switch. What do I do now? I wish Floyd would say something, dammit, but he's probably afraid of making things worse...
I'll wait until time zero – no, it's not that critical, let's say an extra minute – then I'll zap him and we'll go over to manual...
From far, far away there came a faint, whistling scream, like the sound of a tornado marching just below the edge of the horizon. Discovery started to vibrate; there was the first intimation of returning gravity.
'Ignition,' said Hal. 'Full thrust at T plus fifteen seconds.'
'Thank ,you, Hal,' replied Chandra.
48 – Over the Nightside
To Heywood Floyd, aboard the suddenly unfamiliar – because no longer weightless – environment of Leonov's flight deck, the sequence of events had seemed more like a classic slow-motion nightmare than reality. Only once before in his life had he known a similar situation, when he had been in the back of a car during an uncontrollable skid. There had been that same sense of utter helplessness – coupled with the thought: This doesn't really matter – it's not actually happening to me.
Now that the firing sequence had started, his mood changed; everything seemed real again. It was working out exactly as they had planned; Hal was guiding them safely back to Earth. With every minute that passed, their future was becoming more secure; Floyd began slowly to relax, even though he remained alert to all that was happening around him.
For the very last time – and when would any man come here again? – he was flying over the nightside of the greatest of planets, encompassing the volume of a thousand Earths. The ships had been rolled so that Leonov was between Discovery and Jupiter, and their view of the mysteriously glimmering cloudscape was not blocked. Even now, dozens of instruments were busily probing and recording; Hal would continue the work when they were gone.
Since the immediate crisis was over, Floyd moved cautiously 'down' from the flight deck-how strange to feel weight again, even if it was only ten kilos! – and joined Zenia and Katerina in the observation lounge. Apart from the very faintest of red emergency lights, it had been completely blacked out so that they could admire the view with unimpaired night vision. He felt sorry for Max Brailovsky and Sasha Kovalev, who were sitting in the airlock, fully suited up, missing the marvellous spectacle. They had to be ready to leave at a moment's notice to cut the straps securing the ships together – if any of the explosive charges failed to operate.
Jupiter filled the entire sky; it was a mere five hundred kilometres away, so they could see only a tiny fraction of its surface – no more than one could see of Earth from an altitude of fifty kilometres. As his eyes grew accustomed to the dim light, most of it reflected from the icy crust of distant Europa, Floyd could make out a surprising amount of detail. There was no colour at the low level of illumination – except for a hint of red here and there – but the banded structure of the clouds was very distinct, and he could see the edge of a small cyclonic storm looking like an oval island covered with snow. The Great Black Spot had long since fallen astern, and they would not see it again until they were well on the way home.
Down there beneath the clouds, occasional explosions of light flared, many of them obviously caused by the Jovian equivalent of thunderstorms. But other glows and outbursts of luminescence were more long-lived, and of more uncertain origin. Sometimes rings of light would spread out like shock waves from a central source; and occasional rotating beams and fans occurred. It required little imagination to pretend that they were proof of a technological civilization down beneath those clouds – the lights of cities, the beacons of airports. But radar and balloon probes had long ago proved that nothing solid was down there for thousands upon thousands of kilometres, all the way to the unattainable core of the planet.
Midnight on Jupiter! The last close-up glimpse was a magical interlude he would remember all his life. He could enjoy it all the more because, surely, nothing could now go wrong; and even if it did, he would have no reason to reproach himself He had done everything possible to ensure success.
It was very quiet in the
lounge; no one wished to speak as the carpet of clouds unrolled swiftly beneath them. Every few minutes Tanya or Vasili announced the status of the burn; toward the end of Discovery's firing time, tension began to increase again. This was the critical moment – and no one knew exactly when it would be. There was some doubt as to the accuracy of the fuel gauges, and the burn would continue until they were completely dry.
'Estimated cut-off in ten seconds,' said Tanya. 'Walter, Chandra – get ready to come back. Max, Vasili – stand by in case you're needed. Five... four... three... two... one... zero!'
There was no change; the faint scream of Discovery's engines still reached them through the thickness of the two hulls, and the thrust-induced weight still continued to grip their limbs. We're in luck, thought Floyd; the gauges must have been reading low, after all. Every second of extra firing was a bonus; it might even mean the difference between life and death. And how strange to hear a countup instead of a countdown!
five seconds... ten seconds... thirteen seconds. That's it – lucky thirteen!'
Weightlessness, and silence, returned. On both ships, there was a brief burst of cheering. It was quickly truncated, for much was still to be done – and it had to be done swiftly.
Floyd was tempted to go to the airlock so that he could give his congratulations to Chandra and Curnow as soon as they came aboard. But he would only be in the way; the airlock would be a very busy place as Max and Sasha prepared for their possible EVA and the tubeway joining the two ships was disconnected. He would wait in the lounge, to greet the returning heroes.
And he could now relax even further – perhaps from eight to seven, on a scale of ten. For the first time in weeks, he could forget about the radio cut-off. It would never be needed; Hal had performed impeccably. Even if he wished, he could do nothing to affect the mission since Discovery's last drop of propellant had been exhausted.
'All aboard,' announced Sasha. 'Hatches sealed. I'm going to fire the charges.'
There was not the faintest sound as the explosives were detonated, which surprised Floyd; he had expected some noise to be transmitted through the straps, taut as steel bands, that linked the ships together. But there was no doubt that they had gone off as planned, for Leonov gave a series of tiny shudders, as if someone was tapping on the hull. A minute later, Vasili triggered the attitude jets for a single brief burst.
'We're free!' he shouted. 'Sasha, Max – you won't be needed! Everyone get to your hammocks – ignition in one hundred seconds!'
And now Jupiter was rolling away, and a strange new shape appeared outside the window – the long, skeletal frame of Discovery, navigation lights still shining as it drifted away from them and into history. No time remained for sentimental farewells; in less than a minute Leonov's drive would start to operate.
Floyd had never heard it under full power and wanted to protect his ears from the roaring scream that now filled the universe. Leonov's designers had not wasted payload on sound-insulation that would be needed for only a few hours of a voyage that would last for years. And his weight seemed enormous – yet it was barely a quarter of that which he had known all his life.
Within minutes, Discovery had vanished astern, though the flash of its warning beacon could be seen until it had dropped below the horizon. Once again, Floyd told himself, I'm rounding Jupiter – this time gaining speed, not losing it. He glanced across at Zenia, just visible in the darkness with her nose pressed to the observation window. Was she also recalling that last occasion, when they shared the hammock together? There was no danger of incineration now; at least she would not be terrified of that particular fate. Anyway, she seemed a much more confident and cheerful person, undoubtedly thanks to Max – and perhaps Walter as well.
She must have become aware of his scrutiny, for she turned and smiled, then gestured toward the unwinding cloudscape below.
'Look!' she shouted in his ear, 'Jupiter has a new moon!'
What is she trying to say? Floyd asked himself. Her English still isn't very good, but she couldn't possibly have made a mistake in a simple sentence like that. I'm sure I heard her correctly – yet she's pointing downward, not upward.
And then he realized that the scene immediately below them had become much brighter; he could even see yellows and greens that had been quite invisible before. Something far more brilliant than Europa was shining on the Jovian clouds.
Leonov itself, many times brighter than Jupiter's noonday sun, had brought a false dawn to the world it was leaving forever. A hundred-kilometre-long plume of incandescent plasma was trailing behind the ship, as the exhaust from the Sakharov Drive dissipated its remaining energies in the vacuum of space.
Vasili was making an announcement, but the words were completely unintelligible. Floyd glanced at his watch; yes, that would be right about now. They had achieved Jupiter escape velocity. The giant could never recapture them.
And then, thousands of kilometres ahead, a great bow of brilliant light appeared in the sky – the first glimpse of the real Jovian dawn, as full of promise as any rainbow on Earth. Seconds later the Sun leaped up to greet them – the glorious Sun, that would now grow brighter and closer every day.
A few more minutes of steady acceleration, and Leonov would be launched irrevocably on the long voyage home. Floyd felt an overwhelming sense of relief and relaxation. The immutable laws of celestial mechanics would guide him through the inner Solar System, past the tangled orbits of the asteroids, past Mars – nothing could stop him from reaching Earth.
In the euphoria of the moment, he had forgotten all about the mysterious black stain, expanding across the face of Jupiter.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
49 – Devourer of Worlds
They saw it again the next morning, ship's time, as it came around to the dayside of Jupiter. The area of darkness had now spread until it covered an appreciable fraction of the planet, and at last they were able to study it at leisure, and in detail.
'Do you know what it reminds me of?' said Katerina. 'A virus attacking a cell. The way a phage injects its DNA into a bacterium, and then multiplies until it takes over.'
'Are you suggesting,' asked Tanya incredulously, 'that Zagadka is eating Jupiter?'
'It certainly looks like it.'
'No wonder Jupiter is beginning to look sick. But hydrogen and helium won't make a very nourishing diet, and there's not much else in that atmosphere. Only a few percent of other elements.'
'Which adds up to some quintillions of tons of sulphur and carbon and phosphorus and everything else at the lower end of the periodic table,' Sasha pointed out. 'In any case, we're talking about a technology that can probably do anything that doesn't defy the laws of physics. If you have hydrogen, what more do you need? With the right know-how, you can synthesize all the other elements from it.'
'They're sweeping up Jupiter – that's for sure,' said Vasili. 'Look at this.'
An extreme close-up of one of the myriad identical rectangles was now displayed on the telescope monitor. Even to the naked eye, it was obvious that streams of gas were flowing into the two smaller faces; the patterns of turbulence looked very much like the lines of force revealed by iron filings, clustered around the ends of a bar magnet.
'A million vacuum cleaners,' said Curnow, 'sucking up Jupiter's atmosphere. But why? And what are they doing with it?'
'And how do they reproduce?' asked Max. 'Have you caught any of them in the act?'
'Yes and no,' answered Vasili. 'We're too far away to see details, but it's a kind of fission – like an amoeba.'
'You mean – they split in two, and the halves grow back to the original size?'
'Nyet. There aren't any little Zagadki – they seem to grow until they've doubled in thickness, then split down the middle to produce identical twins, exactly the same size as the original. And the cycle repeats itself in approximately two hours.'
'Two hours!' exclaimed Floyd. 'No wonder that they've spread over
half the planet. It's a textbook case of exponential growth.'
'I know what they are!' said Ternovsky in sudden excitement. 'They're von Neumann machines!'
'I believe you're right,' said Vasili. 'But that still doesn't explain what they're doing. Giving them a label isn't all that much help.'
'And what,' asked Katerina plaintively, 'is a von Neumann machine? Explain, please.'
Orlov and Floyd started speaking simultaneously. They stopped in some confusion, then Vasili laughed and waved to the American.
'Suppose you had a very big engineering job to do, Katerina – and I mean big, like strip-mining the entire face of the Moon. You could build millions of machines to do it, but that might take centuries. If you were clever enough, you'd make just one machine – but with the ability to reproduce itself from the raw materials around it. So you'd start a chain reaction, and in a very short time, you'd have bred enough machines to do the job in decades, instead of millennia. With a sufficiently high rate of reproduction, you could do virtually anything in as short a period of time as you wished. The Space Agency's been toying with the idea for years – and I know you have as well, Tanya.'
'Yes: exponentiating machines. One idea that even Tsiolkovski didn't think of.'
'I wouldn't care to bet on that,' said Vasili. 'So it looks, Katerina, as if your analogy was pretty close. A bacteriophage is a von Neumann machine.'
'Aren't we all?' asked Sasha. 'I'm sure Chandra would say so.'
Chandra nodded his agreement.
'That's obvious. In fact, von Neumann got the original idea from studying living systems.'
'And these living machines are eating Jupiter!'
'It certainly looks like it,' said Vasili. 'I've been doing some calculations, and I can't quite believe the answers – even though it's simple arithmetic.'
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