The Sentinel

  It came again, following exactly the same pattern. Now that he was prepared for it, he estimated the length of the sequence; from first faint throb to final crescendo, it lasted just over ten seconds.

  And this time there was a real echo, very faint and far away. Perhaps it came from one of the many reflecting layers, deeper in this stratified atmosphere; perhaps it was another, more distant source. Falcon waited for a second echo, but it never came.

  Mission Control reacted quickly and asked him to drop another probe at once. With two microphones operating, it would be possible to find the approximate location of the sources. Oddly enough, none of Kon-Tiki’s own external mikes could detect anything except wind noises. The boomings, whatever they were, must have been trapped and channeled beneath an atmospheric reflecting layer far below.

  They were coming, it was soon discovered, from a cluster of sources about twelve hundred miles away. The distance gave no indication of their power; in Earth’s oceans, quite feeble sounds could travel equally far. And as for the obvious assumption that living creatures were responsible, the Chief Exobiologist quickly ruled that out.

  “I’ll be very disappointed,” said Dr. Brenner, “if there are no microorganisms or plants here. But nothing like animals, because there’s no free oxygen. All biochemical reactions on Jupiter must be low-energy ones—there’s just no way an active creature could generate enough power to function.”

  Falcon wondered if this was true; he had heard the argument before, and reserved judgment.

  “In any case,” continued Brenner, “some of those sound waves are a hundred yards long! Even an animal as big as a whale couldn’t produce them. They must have a natural origin.”

  Yes, that seemed plausible, and probably the physicists would be able to come up with an explanation. What would a blind alien make, Falcon wondered, of the sounds he might hear when standing beside a stormy sea, or a geyser, or a volcano, or a waterfall? He might well attribute them to some huge beast.

  About an hour before sunrise the voices of the deep died away, and Falcon began to busy himself with preparation for the dawn of his second day. Kon-Tiki was now only three miles above the nearest cloud layer; the external pressure had risen to ten atmospheres, and the temperature was a tropical thirty degrees. A man could be comfortable here with no more equipment than a breathing mask and the right grade of heliox mixture.

  “We’ve some good news for you,” Mission Control reported, soon after dawn. “The cloud layer’s breaking up. You’ll have partial clearing in an hour—but watch out for turbulence.”

  “I’ve already noticed some,” Falcon answered. “How far down will I be able to see?”

  “At least twelve miles, down to the second thermocline. That cloud deck is solid—it never breaks.”

  And it’s out of my reach, Falcon told himself; the temperature down there must be over a hundred degrees. This was the first time that any balloonist had ever had to worry, not about his ceiling, but about his basement!

  Ten minutes later he could see what Mission Control had already observed from its superior vantage point. There was a change in color near the horizon, and the cloud layer had become ragged and humpy, as if something had torn it open. He turned up his little nuclear furnace and gave Kon-Tiki another three miles of altitude, so that he could get a better view.

  The sky below was clearing rapidly, completely, as if something was dissolving the solid overcast. An abyss was opening before his eyes. A moment later he sailed out over the edge of a cloud canyon about twelve miles deep and six hundred miles wide.

  A new world lay spread beneath him; Jupiter had stripped away one of its many veils. The second layer of clouds, unattainably far below, was much darker in color than the first. It was almost salmon pink, and curiously mottled with little islands of brick red. They were all oval-shaped, with their long axes pointing east-west, in the direction of the prevailing wind. There were hundreds of them, all about the same size, and they reminded Falcon of puffy little cumulus clouds in the terrestrial sky.

  He reduced buoyancy, and Kon-Tiki began to drop down the face of the dissolving cliff. It was then that he noticed the snow.

  White flakes were forming in the air and drifting slowly downward. Yet it was much too warm for snow—and, in any event, there was scarcely a trace of water at this altitude. Moreover, there was no glitter or sparkle about these flakes as they went cascading down into the depths. When, presently, a few landed on an instrument boom outside the main viewing port, he saw that they were a dull, opaque white—not crystalline at all—and quite large—several inches across. They looked like wax, and Falcon guessed that this was precisely what they were. Some chemical reaction was taking place in the atmosphere around him, condensing out the hydrocarbons floating in the Jovian air.

  About sixty miles ahead, a disturbance was taking place in the cloud layer. The little red ovals were being jostled around, and were beginning to form a spiral—the familiar cyclonic pattern so common in the meteorology of Earth. The vortex was emerging with astonishing speed; if that was a storm ahead, Falcon told himself, he was in big trouble.

  And then his concern changed to wonder—and to fear. What was developing in his line of flight was not a storm at all. Something enormous—something scores of miles across—was rising through the clouds.

  The reassuring thought that it, too, might be a cloud—a thunderhead boiling up from the lower levels of the atmosphere—lasted only a few seconds. No; this was solid. It shouldered its way through the pink-and-salmon overcast like an iceberg rising from the deeps.

  An iceberg floating on hydrogen? That was impossible, of course; but perhaps it was not too remote an analogy. As soon as he focused the telescope upon the enigma, Falcon saw that it was a whitish, crystalline mass, threaded with streaks of red and brown. It must be, he decided, the same stuff as the “snowflakes” falling around him—a mountain range of wax. And it was not, he soon realized, as solid as he had thought; around the edges it was continually crumbling and reforming . . .

  “I know what it is,” he radioed Mission Control, which for the last few minutes had been asking anxious questions. “It’s a mass of bubbles—some kind of foam. Hydrocarbon froth. Get the chemists working on . . . Just a minute!”

  “What is it?” called Mission Control. “What is it?”

  He ignored the frantic pleas from space and concentrated all his mind upon the image in the telescope field. He had to be sure; if he made a mistake, he would be the laughingstock of the solar system.

  Then he relaxed, glanced at the clock, and switched off the nagging voice from Jupiter V.

  “Hello, Mission Control,” he said, very formally. “This is Howard Falcon aboard Kon-Tiki. Ephemeris Time nineteen hours twenty-one minutes fifteen seconds. Latitude zero degrees five minutes North. Longitude one hundred five degrees forty-two minutes, System One.

  “Tell Dr. Brenner that there is life on Jupiter. And it’s big . . . ”

  5. The wheels of Poseidon

  “I’m very happy to be proved wrong,” Dr. Brenner radioed back cheerfully. “Nature always has something up her sleeve. Keep the long-focus camera on target and give us the steadiest pictures you can.”

  The things moving up and down those waxen slopes were still too far away for Falcon to make out many details, and they must have been very large to be visible at all at such a distance. Almost black, and shaped like arrowheads, they maneuvered by slow undulations of their entire bodies, so that they looked rather like giant manta rays, swimming above some tropical reef.

  Perhaps they were sky-born cattle, browsing on the cloud pastures of Jupiter, for they seemed to be feeding along the dark, red-brown streaks that ran like dried-up river beds down the flanks of the floating cliffs. Occasionally, one of them would dive headlong into the mountain of foam and disappear completely from sight.

  Kon-Tiki was moving only slowly with respect to the cloud layer below; it would be at least three hours before she was above those
ephemeral hills. She was in a race with the Sun. Falcon hoped that darkness would not fall before he could get a good view of the mantas, as he had christened them, as well as the fragile landscape over which they flapped their way.

  It was a long three hours. During the whole time, he kept the external microphones on full gain, wondering if here was the source of that booming in the night. The mantas were certainly large enough to have produced it; when he could get an accurate measurement, he discovered that they were almost a hundred yards across the wings. That was three times the length of the largest whale—though he doubted if they could weigh more than a few tons.

  Half an hour before sunset, Kon-Tiki was almost above the “mountains.”

  “No,” said Falcon, answering Mission Control’s repeated questions about the mantas, “they’re still showing no reaction to me. I don’t think they’re intelligent—they look like harmless vegetarians. And even if they try to chase me, I’m sure they can’t reach my altitude.”

  Yet he was a little disappointed when the mantas showed not the slightest interest in him as he sailed high above their feeding ground. Perhaps they had no way of detecting his presence. When he examined and photographed them through the telescope, he could see no signs of any sense organs. The creatures were simply huge black deltas, rippling over hills and valleys that, in reality, were little more substantial than the clouds of Earth. Though they looked solid, Falcon knew that anyone who stepped on those white mountains would go crashing through them as if they were made of tissue paper.

  At close quarters he could see the myriads of cellules or bubbles from which they were formed. Some of these were quite large—a yard or so in diameter—and Falcon wondered in what witches’ cauldron of hydrocarbons they had been brewed. There must be enough petrochemicals deep down in the atmosphere of Jupiter to supply all Earth’s needs for a million years.

  The short day had almost gone when he passed over the crest of the waxen hills, and the light was fading rapidly along their lower slopes. There were no mantas on this western side, and for some reason the topography was very different. The foam was sculptured into long, level terraces, like the interior of a lunar crater. He could almost imagine that they were gigantic steps leading down to the hidden surface of the planet.

  And on the lowest of those steps, just clear of the swirling clouds that the mountain had displaced when it came surging skyward, was a roughly oval mass, one or two miles across. It was difficult to see, since it was only a little darker than the gray-white foam on which it rested. Falcon’s first thought was that he was looking at a forest of pallid trees, like giant mushrooms that had never seen the Sun.

  Yes, it must be a forest—he could see hundreds of thin trunks, springing from the white waxy froth in which they were rooted. But the trees were packed astonishingly close together; there was scarcely any space between them. Perhaps it was not a forest, after all, but a single enormous tree—like one of the giant multi-trunked banyans of the East. Once he had seen a banyan tree in Java that was over six hundred and fifty yards across; this monster was at least ten times that size.

  The light had almost gone. The cloudscape had turned purple with refracted sunlight, and in a few seconds that, too, would have vanished. In the last light of his second day on Jupiter, Howard Falcon saw—or thought he saw—something that cast the gravest doubts on his interpretation of the white oval.

  Unless the dim light had totally deceived him, those hundreds of thin trunks were beating back and forth, in perfect synchronism, like fronds of kelp rocking in the surge.

  And the tree was no longer in the place where he had first seen it.

  “Sorry about this,” said Mission Control, soon after sunset, “but we think Source Beta is going to blow within the next hour. Probability seventy percent.”

  Falcon glanced quickly at the chart. Beta—Jupiter latitude one hundred and forty degrees—was over eighteen thousand six hundred miles away and well below his horizon. Even though major eruptions ran as high as ten megatons, he was much too far away for the shock wave to be a serious danger. The radio storm that it would trigger was, however, quite a different matter.

  The decameter outbursts that sometimes made Jupiter the most powerful radio source in the whole sky had been discovered back in the 1950s, to the utter astonishment of the astronomers. Now, more than a century later, their real cause was still a mystery. Only the symptoms were understood; the explanation was completely unknown.

  The “volcano” theory had best stood the test of time, although no one imagined that this word had the same meaning on Jupiter as on Earth. At frequent intervals—often several times a day—titanic eruptions occurred in the lower depths of the atmosphere, probably on the hidden surface of the planet itself. A great column of gas, more than six hundred miles high, would start boiling upward as if determined to escape into space.

  Against the most powerful gravitational field of all the planets, it had no chance. Yet some traces—a mere few million tons—usually managed to reach the Jovian ionosphere; and when they did, all hell broke loose.

  The radiation belts surrounding Jupiter completely dwarf the feeble Van Allen belts of Earth. When they are short-circuited by an ascending column of gas, the result is an electrical discharge millions of times more powerful than any terrestrial flash of lightning; it sends a colossal thunderclap of radio noise flooding across the entire solar system and on out to the stars.

  It had been discovered that these radio outbursts came from four main areas of the planet. Perhaps there were weaknesses there that allowed the fires of the interior to break out from time to time. The scientists on Ganymede, largest of Jupiter’s many moons, now thought that they could predict the onset of a decameter storm; their accuracy was about as good as a weather forecaster’s of the early 1900s.

  Falcon did not know whether to welcome or to fear a radio storm; it would certainly add to the value of the mission—if he survived it. His course had been planned to keep as far as possible from the main centers of disturbance, especially the most active one, Source Alpha. As luck would have it, the threatening Beta was the closest to him. He hoped that the distance, almost three-fourths the circumference of Earth, was safe enough.

  “Probability ninety percent,” said Mission Control with a distinct note of urgency. “And forget that hour. Ganymede says it may be any moment.”

  The radio had scarcely fallen silent when the reading on the magnetic field-strength meter started to shoot upward. Before it could go off scale, it reversed and began to drop as rapidly as it had risen. Far away and thousands of miles below, something had given the planet’s molten core a titanic jolt.

  “There she blows!” called Mission Control.

  “Thanks, I already know. When will the storm hit me?”

  “You can expect onset in five minutes. Peak in ten.”

  Far around the curve of Jupiter, a funnel of gas as wide as the Pacific Ocean was climbing spaceward at thousands of miles an hour. Already the thunderstorms of the lower atmosphere would be raging around it—but they were nothing compared with the fury that would explode when the radiation belt was reached and began dumping its surplus electrons onto the planet. Falcon began to retract all the instrument booms that were extended out from the capsule. There were no other precautions he could take. It would be four hours before the atmospheric shock wave reached him—but the radio blast, traveling at the speed of light, would be here in a tenth of a second, once the discharge had been triggered.

  The radio monitor, scanning back and forth across the spectrum, still showed nothing unusual, just the normal mush of background static. Then Falcon noticed that the noise level was slowly creeping upward. The explosion was gathering its strength.

  At such a distance he had never expected to see anything. But suddenly a flicker as of far-off heat lightning danced along the eastern horizon. Simultaneously, half the circuit breakers jumped out of the main switchboard, the lights failed, and all communications channels w
ent dead.

  He tried to move, but was completely unable to do so. The paralysis that gripped him was not merely psychological; he seemed to have lost all control of his limbs and could feel a painful tingling sensation over his entire body. It was impossible that the electric field could have penetrated this shielded cabin. Yet there was a flickering glow over the instrument board, and he could hear the unmistakable crackle of a brush discharge.

  With a series of sharp bangs, the emergency systems went into operation, and the overloads reset themselves. The lights flickered on again. And Falcon’s paralysis disappeared as swiftly as it had come.

  After glancing at the board to make sure that all circuits were back to normal, he moved quickly to the viewing ports.

  There was no need to switch on the inspection lamps—the cables supporting the capsule seemed to be on fire. Lines of light glowing an electric blue against the darkness stretched upward from the main lift ring to the equator of the giant balloon; and rolling slowly along several of them were dazzling balls of fire.

  The sight was so strange and so beautiful that it was hard to read any menace in it. Few people, Falcon knew, had ever seen ball lightning from such close quarters—and certainly none had survived if they were riding a hydrogen-filled balloon back in the atmosphere of Earth. He remembered the flaming death of the Hindenburg, destroyed by a stray spark when she docked at Lakehurst in 1937; as it had done so often in the past, the horrifying old newsreel film flashed through his mind. But at least that could not happen here, though there was more hydrogen above his head than had ever filled the last of the Zeppelins. It would be a few billion years yet, before anyone could light a fire in the atmosphere of Jupiter.

  With a sound like briskly frying bacon, the speech circuit came back to life.

  “Hello, Kon-Tiki—are you receiving? Are you receiving?”

  The words were chopped and badly distorted, but intelligible. Falcon’s spirits lifted; he had resumed contact with the world of men.