Only along the equator was bare rock visible; here was an incredibly jagged no-man's-land of canyons and jumbled boulders, forming a darker band that completely surrounded the little world. There were a few impact craters, but no sign of vulcanism; Europa had obviously never possessed any internal sources of heat.
There was, as had long been known, a trace of atmosphere. When the dark edge of the satellite passed across a star, it dimmed briefly before the moment of eclipse. And in some areas there was a hint of cloud—perhaps a mist of ammonia droplets, borne on tenuous methane winds.
As swiftly as it had rushed out of the sky ahead, Europa dropped astern; and now Jupiter itself was only two hours away. Hal had checked and rechecked the ship's orbit with infinite care, and there was no need for further speed corrections until the moment of closest approach. Yet, even knowing this, it was a strain on the nerves to watch that giant globe ballooning minute by minute. It was difficult to believe that Discovery was not plunging directly into it, and that the planet's immense gravitational field was not dragging them down to destruction.
Now was the time to drop the atmospheric probes—which, it was hoped, would survive long enough to send back some information from below the Jovian cloud deck. Two stubby, bomb-shaped capsules, enclosed in ablative heat-shields, were gently nudged into orbits which for the first few thousand miles deviated scarcely at all from that of Discovery.
But they slowly drifted away; and now, at last, even the unaided eye could see what Hal had been asserting. The ship was in a near-grazing orbit, not a collision one; she would miss the atmosphere. True, the difference was only a few hundred miles—a mere nothing, when one was dealing with a planet ninety thousand miles in diameter—but that was enough.
Jupiter now filled the entire sky; it was so huge that neither mind nor eye could grasp it any longer, and both had abandoned the attempt. If it had not been for the extraordinary variety of color—the reds and pinks and yellows and salmons and even scarlets—of the atmosphere beneath them, Bowman could have believed that he was flying low over a cloudscape on Earth.
And now, for the first time in all their journeying, they were about to lose the Sun. Pale and shrunken though it was, it had been Discovery's constant companion since her departure from Earth, five months ago. But now her orbit was diving into the shadow of Jupiter; she would soon pass over the night side of the planet.
A thousand miles ahead, the band of twilight was hurtling toward them; behind, the Sun was sinking swiftly into the Jovian clouds. Its rays spread out along the horizon like two flaming, down-turned horns, then contracted and died in a brief blaze of chromatic glory. The night had come.
And yet—the great world below was not wholly dark. It was awash with phosphorescence, which grew brighter minute by minute as their eyes grew accustomed to the scene. Dim rivers of light were flowing from horizon to horizon, like the luminous wakes of ships on some tropical sea. Here and there they gathered into pools of liquid fire, trembling with vast, submarine disturbances welling up from the hidden heart of Jupiter. It was a sight so awe-inspiring that Poole and Bowman could have stared for hours; was this, they wondered, merely the result of chemical and electrical forces down there in that seething caldron—or was it the by-product of some fantastic form of life? These were questions which scientists might still be debating when the newborn century drew to its close.
As they drove deeper and deeper into the Jovian night, the glow beneath them grew steadily brighter. Once Bowman had flown over northern Canada during the height of an auroral display; the snow-covered landscape had been as bleak and brilliant as this. And that arctic wilderness, he reminded himself, was more than a hundred degrees warmer than the regions over which they were hurtling now.
"Earth signal is fading rapidly," announced Hal. "We are entering the first diffraction zone."
They had expected this—indeed, it was one of the mission's objectives, as the absorption of radio waves would give valuable information about the Jovian atmosphere. But now that they had actually passed behind the planet, and it was cutting off communication with Earth, they felt a sudden overwhelming loneliness. The radio blackout would last only an hour; then they would emerge from Jupiter's eclipsing screen, and could resume contact with the human race. That hour, however, would be one of the longest of their lives.
Despite their relative youth, Poole and Bowman were veterans of a dozen space voyages, but now they felt like novices. They were attempting something for the first time; never before had any ship traveled at such speeds, or braved so intense a gravitational field. The slightest error in navigation at this critical point and Discovery would go speeding on toward the far limits of the Solar System, beyond any hope of rescue.
The slow minutes dragged by. Jupiter was now a vertical wall of phosphorescence stretching to infinity above them—and the ship was climbing straight up its glowing face. Though they knew that they were moving far too swiftly for even Jupiter's gravity to capture them, it was hard to believe that Discovery had not become a satellite of this monstrous world.
At last, far ahead, there was a blaze of light along the horizon. They were emerging from shadow, heading out into the Sun. And at almost the same moment Hal announced: "I am in radio contact with Earth. I am also happy to say that the perturbation maneuver has been successfully completed. Our time to Saturn is one hundred and sixty-seven days, five hours, eleven minutes."
That was within a minute of the estimate; the fly-by had been carried out with impeccable precision. Like a ball on a cosmic pool table, Discovery had bounced off the moving gravitational field of Jupiter, and had gained momentum from the impact. Without using any fuel, she had increased her speed by several thousand miles an hour.
Yet there was no violation of the laws of mechanics; Nature always balances her books, and Jupiter had lost exactly as much momentum as Discovery had gained. The planet had been slowed down—but as its mass was a sextillion times greater than the ship's, the change in its orbit was far too small to be detectable. The time had not yet come when Man could leave his mark upon the Solar System.
As the light grew swiftly around them, and the shrunken Sun lifted once more into the Jovian sky, Poole and Bowman reached out silently and shook each other's hands.
Though they could hardly believe it, the first part of the mission was safely over.
Chapter 20
The World of the Gods
But they had not yet finished with Jupiter. Far behind, the two probes that Discovery had launched were making contact with the atmosphere.
One was never heard from again; presumably it made too steep an entry, and burned up before it could send any information. The second was more successful; it sliced though the upper layers of the Jovian atmosphere, then skimmed out once more into space. As had been planned, it had lost so much speed by the encounter that it fell back again along a great ellipse. Two hours later, it reentered atmosphere on the daylight side of the planet—moving at seventy thousand miles an hour.
Immediately, it was wrapped in an envelope of incandescent gas, and radio contact was lost. There were anxious minutes of waiting, then, for the two watchers on the control deck. They could not be certain that the probe would survive, and that the protective ceramic shield would not burn completely away before braking had finished. If that happened, the instruments would be vaporized in a fraction of a second.
But the shield held, long enough for the glowing meteor to come to rest. The charred fragments were jettisoned, the robot thrust out its antennas and began to peer around with its electronic senses. Aboard Discovery, now almost a quarter of a million miles away, the radio started to bring in the first authentic news from Jupiter.
The thousands of pulses pouring in every second were reporting atmospheric composition, pressure, temperature, magnetic fields, radioactivity, and dozens of other factors which only the experts on Earth could unravel. However, there was one message that could be understood instantly; it was the TV picture, in fu
ll color, sent back by the falling probe.
The first views came when the robot had already entered the atmosphere, and had discarded its protective shell. All that was visible was a yellow mist, flecked with patches of scarlet which moved past the camera at a dizzying rate—streaming upwards as the probe fell at several hundred miles an hour.
The mist grew thicker; it was impossible to guess whether the camera was seeing for ten inches or ten miles, because there were no details on which the eye could focus. It seemed that, as far as the TV system was concerned, the mission was a failure. The equipment had worked, but there was nothing to see in this foggy, turbulent atmosphere.
And then, quite abruptly, the mist vanished. The probe must have fallen through the base of a high layer of cloud, and come out into a clear zone—perhaps a region of almost pure hydrogen with only a sparse scattering of ammonia crystals. Though it was still quite impossible to judge the scale of the picture, the camera was obviously seeing for miles.
The scene was so alien that for a moment it was almost meaningless to eyes accustomed to the colors and shapes of Earth. Far, far below lay an endless sea of mottled gold, scarred with parallel ridges that might have been the crests of gigantic waves. But there was no movement; the scale of the scene was too immense to show it. And that golden vista could not possibly have been an ocean, for it was still high in the Jovian atmosphere. It could only have been another layer of cloud.
Then the camera caught, tantalizingly blurred by distance, a glimpse of something very strange. Many miles away, the golden landscape reared itself into a curiously symmetrical cone, like a volcanic mountain. Around the summit of that cone was a halo of small, puffy clouds—all about the same size, all quite distinct and isolated. There was something disturbing and unnatural about them—if, indeed, the word "natural" could ever be applied to this awesome panorama.
Then, caught by some turbulence in the rapidly thickening atmosphere, the probe twisted around to another quarter of the horizon, and for a few seconds the screen showed nothing but a golden blur. Presently it stabilized; the "sea" was much closer, but as enigmatic as ever. One could now observe that it was interrupted here and there with patches of darkness, which might have been holes or gaps leading to still deeper layers of the atmosphere.
The probe was destined never to reach them. Every mile, the density of the gas around it had been doubling, the pressure mounting as it sank deeper and deeper toward the hidden surface of the planet. It was still high above that mysterious sea when the picture gave one premonitory flicker, then vanished, as the first explorer from Earth crumpled beneath the weight of the miles of atmosphere above it.
It had given, in its brief life, a glimpse of perhaps one millionth of Jupiter, and had barely approached the planet's surface, hundreds of miles down in the deepening mists. When the picture faded from the screen, Bowman and Poole could only sit in silence, turning the same thought over in their minds.
The ancients had, indeed, done better than they knew when they named this world after the lord of all the gods. If there was life down there, how long would it take even to locate it? And after that, how many centuries before men could follow this first pioneer—in what kind of ship?
But these matters were now no concern of Discovery and her crew. Their goal was a still stranger world, almost twice as far from the Sun—across another half billion miles of comet-haunted emptiness.
PART FOUR
ABYSS
Chapter 21
Birthday Party
The familiar strains of "Happy Birthday," hurled across seven hundred million miles of space at the velocity of light, died away among the vision screens and instrumentation of the control deck. The Poole family, grouped rather self-consciously round the birthday cake on Earth, lapsed into a sudden silence.
Then Mr. Poole, Senior, said gruffly: "Well, Frank, can't think of anything else to say at the moment, except that our thoughts are with you, and we're wishing you the happiest of birthdays."
"Take care, darling," Mrs. Poole interjected tearfully. "God bless you."
There was a chorus of "good-byes," and the vision screen went blank. How strange to think, Poole told himself, that all this had happened more than an hour ago; by now his family would have dispersed again and its members would be miles from home. But in a way that time lag, though it could be frustrating, was also a blessing in disguise. Like every man of his age, Poole took it for granted that he could talk instantly, to anyone on Earth, whenever he pleased. Now that this was no longer true, the psychological impact was profound. He had moved into a new dimension of remoteness, and almost all emotional links had been stretched beyond the yield point.
"Sorry to interrupt the festivities," said Hal, "but we have a problem."
"What is it?" Bowman and Poole asked simultaneously.
"I am having difficulty in maintaining contact with Earth. The trouble is in the AE-35 unit. My Fault Prediction Center reports that it may fail within seventy-two hours."
"We'll take care of it," Bowman replied. "Let's see the optical alignment."
"Here it is, Dave. It's still O.K. at the moment."
On the display screen appeared a perfect half-moon, very brilliant against a background almost free of stars. It was covered with clouds, and showed not one geographical feature that could be recognized. Indeed, at first glance it could be easily mistaken for Venus.
But not at a second one, for there beside it was the real Moon which Venus did not possess—a quarter the size of Earth, and in exactly the same phase. It was easy to imagine that the two bodies were mother and child, as many astronomers had believed, before the evidence of the lunar rocks had proved beyond doubt that the Moon had never been part of Earth.
Poole and Bowman studied the screen in silence for half a minute. This image was coming to them from the long-focus TV camera mounted on the rim of the big radio dish; the cross-wires at its center showed the exact orientation of the antenna. Unless the narrow pencil beam was pointed precisely at Earth, they could neither receive nor transmit. Messages in both directions would miss their target and would shoot, unheard and unseen, out through the Solar System and into the emptiness beyond. If they were ever received, it would not be for centuries—and not by men.
"Do you know where the trouble is?" asked Bowman.
"It's intermittent and I can't localize it. But it appears to be in the AE-35 unit."
"What procedure do you suggest?"
"The best thing would be to replace the unit with a spare, so that we can check it over."
"O.K.—let us have the hard copy."
The information flashed on the display screen; simultaneously, a sheet of paper slid out of the slot immediately beneath it. Despite all the electronic read-outs, there were times when good old-fashioned printed material was the most convenient form of record.
Bowman studied the diagrams for a moment, then whistled.
"You might have told us," he said. "This means going outside the ship."
"I'm sorry," Hal replied. "I assumed you knew that the AE-35 unit was on the antenna mounting."
"I probably did, a year ago. But there are eight thousand subsystems aboard. Anyway, it looks a straightforward job. We only have to unlock a panel and put in a new unit."
"That suits me fine," said Poole, who was the crew member designated for routine extravehicular activity. "I could do with a change of scenery. Nothing personal, of course."
"Let's see if Mission Control agrees," said Bowman. He sat still for a few seconds, marshaling his thoughts, then started to dictate a message.
"Mission Control, this is X-ray-Delta-One. At two-zero-four-five, on-board fault prediction center in our niner-triple-zero computer showed Alpha Echo three five unit as probable failure within seventy-two hours. Request check your telemetry monitoring and suggest you review unit in your ship systems simulator. Also, confirm your approval our plan to go EVA and replace Alpha Echo three five unit prior to failure. Mission Control, this is X-
ray-Delta-One, two-one-zero-three transmission concluded."
Through years of practice, Bowman could switch at a moment's notice to this jargon—which someone had once christened "Technish"—and back again to normal speech, without clashing his mental gears. Now there was nothing to do but to wait for the confirmation, which would take at least two hours as the signals made the round trip past the orbits of Jupiter and Mars.
It came while Bowman was trying, without much success, to beat Hal at one of the geometrical pattern games stored in his memory.
"X-ray-Delta-One, this is Mission Control, acknowledging your two-one-zero-three. We are reviewing telemetric information on our mission simulator and will advise.
"Roger your plan to go EVA and replace Alpha-Echo three-five unit prior to possible failure. We are working on test procedures for you to apply to faulty unit."
The serious business having been completed, the Mission Controller reverted to normal English.
"Sorry you fellows are having a bit of trouble, and we don't want to add to your woes. But if it's convenient to you prior to EVA, we have a request from Public Information. Could you do a brief recording for general release, outlining the situation and explaining just what the AE-35 does. Make it as reassuring as you can. We could do it, of course—but it will be much more convincing in your words. Hope this won't interfere too badly with your social life. X-ray-Delta-One, this is Mission Control, two-one-five-five, transmission concluded."
Bowman could not help smiling at the request. There were times when Earth showed a curious insensitivity and lack of tact. "Make it reassuring," indeed!
When Poole joined him at the end of his sleep period, they spent ten minutes composing and polishing the reply. In the early stages of the mission, there had been countless requests from all the news media for interviews, discussions—almost anything that they cared to say. But as the weeks drifted uneventfully past, and the time lag increased from a few minutes to over an hour, interest had gradually slackened. Since the excitement of the Jupiter fly-by, over a month ago, they had made only three or four tapes for general release.