The Hammer of God

by Arthur C. Clarke

  The details of the simulation were so perfect that he could see the bare patches of rock on Kali where the jets of the space-sled had blown away the dust of ages. That was real enough; but the image of ATLAS and its cluster of fuel tanks still belonged to the future—hopefully, only a few days away. With David’s assistance, all the engineering problems of positioning and anchoring the mass-driver had been solved, and there was no reason to suppose that there would be any difficulty in turning theory into practice.

  “Ready to begin run,” said David. “What viewpoint would you like?”

  “North pole of Ecliptic. Ten A.U. distant. Show all orbits.”

  “All? There are 54,372 bodies in that field of view.” The pause while David checked his catalogue was barely perceptible.

  “Sorry. I mean all major planets. And any bodies that come within a thousand kilometers of Kali. Correction—make that a hundred kilometers.”

  Kali and ATLAS vanished. Singh was looking down upon the Solar System from above, with the orbits of Saturn, Jupiter, Mars, Earth, Venus, and Mercury visible as thin, glowing lines. The positions of the planets themselves were indicated by tiny but recognizable icons—Saturn with its rings, Jupiter with its belts, Mars with a tiny polar cap, Earth one vast ocean, Venus a featureless white crescent, Mercury a pockmarked disk.

  And Kali was a skull. That had been David’s own idea, and no one had ever discussed it with him. Presumably he had looked up the entry in the encyclopedia—and seen one of the statues of the Hindu goddess of destruction wearing her sinister necklace.

  “Center on Kali-Earth axis—zoom in—check!”

  Now Singh’s consciousness was filled by that fateful conic section—the ellipse of doom that connected the present positions of Earth and Kali.

  “Time compression?”

  “Ten to fifth.”

  At that rate, every second would represent a day: Kali would reach Earth in a matter of minutes, not months.

  “Starting run.”

  The planets began to move—Mercury speeding around its innermost track, and even lumbering Saturn creeping snaillike along its outer orbit.

  Kali started its fall sunward, still moving under gravity alone. But numbers were flickering somewhere in Singh’s field of consciousness, so swiftly that they blurred together. Suddenly they collapsed to zero, and at the same moment David said, “Ignition!”

  Strange, Singh thought briefly, how some words remained in use long after they had lost their original context. “Ignition” dated back at least a century, to the era of chemical rockets. There was no way that the jet that powered ATLAS—or any other deep-space vessel—could burn. It was pure hydrogen—and even had there been any oxygen present, it would have been far too hot for the low-temperature phenomenon of mere combustion. Any water molecules would have been instantly ripped back to their component atoms.

  More figures appeared, some constant, others changing very slowly. Most prominently displayed was the acceleration produced by the ATLAS jet in this phantom world—mere microgravities, upon a mass the size of Kali. And here were the vital deltas, the barely measurable changes now being made to the asteroid’s velocity and position.

  The days flickered past; the numbers steadily increased: Mercury had moved halfway around the sun, but Kali still showed no visible sign of deviation from its natural orbit. Only the increasing deltas proved that it was stirring sluggishly from its ancient path.

  “Zoom five times,” Singh ordered as Kali passed Mars. The outer planets vanished as the image expanded; but the effect of ATLAS’s days of continuous thrusting was still undetectable.

  “Burnout,” said David abruptly. (Yet another word from the infancy of astronautics!) The figures that had recorded thrust and acceleration dropped instantly to zero. Kali was once more being whirled around the sun by gravity alone.

  “Zoom ten. Reduce time compression to one thousand.”

  Now only Earth, Moon, and Kali occupied Singh’s field of consciousness. On this expanded scale, the asteroid seemed to be moving not along an ellipse, but an almost straight line—and it was a line that did not point toward Earth.

  Singh knew better than to take any hope from that. Kali had yet to pass the Moon and—like a treacherous friend betraying her old companion—she would give Kali’s orbit its last murderous twist.

  Now, in this final stage of the encounter, each second represented three minutes of real time. Kali’s path was bending visibly in the Moon’s gravitational field—bending toward Earth. But the effect of ATLAS’s efforts, though they had ceased “weeks” earlier, was also apparent. The simulation displayed two orbits—the original one, and the one produced by human intervention.

  “Zoom ten. Time compression one hundred.”

  Now one second equaled almost two minutes, and Earth filled Singh’s field of consciousness. But the tiny skull icon had remained the same size: on this scale, Kali was still too small to show a visible disk.

  The virtual Earth looked incredibly real, heartbreakingly beautiful; impossible to believe it was merely a construct of superbly organized megabytes. Down there—if only in David’s memory!—was the glistening white cap of the Antarctic, the continent of Australia, the New Zealand islands, the coast of China. But dominating all was the deep blue of the Pacific; only twenty generations ago it had been as great a challenge to Mankind as were the gulfs of space today.

  “Zoom ten. Keep tracking Kali.”

  The blue curve of horizon was misty with atmosphere, merging imperceptibly into utter blackness. Kali was still dropping toward it, drawn downward and also accelerated by the Earth’s gravitational field—almost as if the planet were abetting its own suicide.

  “Closest approach in one minute.”

  Singh focused his attention on the numbers still flickering at the edge of vision. The message they carried was more precise, though less dramatic, than that given by the simulated image. The all-important one—Kali’s distance from the Earth’s surface—was still decreasing.

  But the rate of decrease was itself decreasing. It was taking longer and longer for Kali to cover each new kilometer Earthward.

  And then the figure stabilized: 523… 523… 522… 522… 522… 523… 523… 524… 524… 525…

  Singh allowed himself the luxury of breath. Kali had made its closest approach, and was drawing away.

  ATLAS could do the job. Now it only remained to match the real world with the virtual one.

  28

  BIRTHDAY PARTY

  “I NEVER EXPECTED,” SAID SIR COLIN, “TO SPEND MY hundredth birthday outside the orbit of Mars. In fact, when I was born, only about one man in ten could hope to reach that age. And one woman in five—which always seemed unfair to me.”

  (Good-natured booing from the four ladies of the crew; groans from the males. A smug “Nature knows best” from ship’s physician Dr. Elizabeth Warden.)

  “But here I am, in reasonably good shape, and I’d like to thank you all for your good wishes. And especially Sonny, for that marvelous vintage we’ve just drunk—Chateau Whateveritwas, 2005!”

  “It was 1905, Prof—not 2005. And you should thank the kitchen programs, not me.”

  “Well, you’re the only person who knows what’s in them. We’d starve to death if you forget what buttons to press.”

  Hundred-year-old geologists could not be expected to kit themselves up properly, so Singh and Fletcher double-checked Draker’s spacesuit before they accompanied him out of the airlock. Movement in the immediate vicinity of Goliath had been greatly simplified by a network of ropes, supported on meter-high rods driven into Kali’s friable outer crust: the ship now looked like a spider in the center of a web.

  The three men moved carefully hand-over-hand to a small space-sled, dwarfed by the spherical propellant tanks that had been lined up for later connection to ATLAS. “Looks as if some lunatic has built an oil refinery on an asteroid” had been the prof’s comment when he saw what Fletcher’s human-plus-robot workers had achie
ved in such an amazingly short time.

  Torin Fletcher, used to working on Deimos, was the only man who could really handle a space-sled in the even feebler gravity of Kali. “You’ve got to be careful,” he had warned would-be jockeys. “A snail with arthritis could reach escape velocity here. We don’t want to waste time and reaction mass hauling you back if you decide to head for Alpha Centauri.”

  With barely perceptible puffs of gas he lifted the sled off the surface of the asteroid and started the leisurely circumnavigation of the world, while Draker eagerly scanned the regions of Kali he had never seen with his unaided eyes. Until now he had been forced to rely on specimens brought back by crew members. And although remote examination via mobile cameras was invaluable, there was no substitute for hands-on experience, aided by skillful hammer blows. Draker had complained that he could never get more than a few meters away from Goliath, because Captain Singh refused to run risks with his most celebrated passenger, and could spare no one to look after him outside the ship. (As if I needed looking after!) But a one-hundredth birthday overruled such objections, and the scientist was like a small boy on his first holiday away from home.

  The sled was gliding over the surface of Kali at comfortable walking speed—assuming that a man could walk on this microworld. Sir Colin kept scanning like an ancient search radar from horizon to horizon (sometimes all of fifty meters distant) occasionally muttering to himself. After less than five minutes they had reached the antipodes: Goliath and ATLAS were both hidden by the bulk of Kali when Draker asked, “Can we stop here? I’d like to get off.”

  “Of course. But we’ll attach a line, in case we have to reel you back.”

  The geologist snorted in disgust, but submitted to the indignity. Then he gently eased himself off the now-motionless sled, and relaxed in free-fall.

  It was not easy to tell that he was indeed falling in this minuscule gravity; it was almost two minutes before he crashed into Kali, from an altitude of a whole meter, moving at a velocity barely perceptible to the naked eye….

  Colin Draker had stood on many asteroids. Sometimes, as on giants like Ceres, it was easy to tell that the force of gravity was dragging you down, even if feebly. Here it took a considerable act of imagination; the slightest movement, and Kali would lose its grip.

  Yet he was, finally and indisputably, standing on the most famous—or infamous—asteroid in the whole of history. Even with his scientific knowledge it was hard for Draker to accept the fact that this tiny, erratically curved fragment of cosmic debris represented a greater threat to humanity than all the warheads stockpiled in the Age of Nuclear Madness.

  Kali’s swift rotation was taking them into night, and as their eyes adapted, they watched the stars come out around them—in exactly the patterns that Earth-based observers would see, for they were still so close to the home planet that the outer universe appeared completely unchanged. However, there was one unfamiliar and surprising object low in the sky—a brilliant yellow star which was not, like all other stars, a dimensionless point of light.

  “Look,” said Sir Colin. “There’s something you’ll never see from Earth—or even Mars.”

  “What about it?” asked Fletcher. “That’s only Saturn.”

  “Of course it is—but look carefully. Very carefully.”

  “Oh, I can see the rings!”

  “Not really; you only think you can—they’re just at the limit of visibility. But your eye can detect something peculiar, and since you know what you’re looking at, your memory fills in the details. Now you know why Saturn gave poor Galileo such a headache. His feeble telescopes showed that there was something odd about the planet, but who would have imagined rings? Then they turned edge-on and disappeared, so he thought his eyes had fooled him. He never did know what he’d been looking at.”

  For a moment the three stared in silence, watching Saturn rise as Kali turned through its brief night, and wondering how much of their eyes’ message they could believe. Then Fletcher said quietly: “Back on board, Prof. We’ve still a long way to go—we’re only halfway around the world.”

  They covered most of the remaining half—and brought up the small but still blinding sun—in the next five minutes. The sled was gliding up the slope of a small hillock when Draker suddenly noticed something almost unbelievable. Only a few dozen meters away (he was getting good at judging distances now) was a splash of brilliant color on the charcoal landscape.

  “Stop!” he cried. “What’s that?”

  His two companions looked in the direction he was pointing, then back at him.

  “I don’t see anything,” said the captain.

  “Probably an afterimage through staring at Saturn. Your eyes haven’t adapted to the daylight,” Fletcher added.

  “Are you blind?! Look!”

  “Better humor the poor fellow,” said Fletcher. “He may get violent—and we don’t want that, do we?”

  He pivoted the sled with effortless skill while Draker sat in stunned silence. A few seconds later the geologist’s astonishment turned to utter incredulity. I am growing mad, he thought.

  Poised on a slender stem half a meter above the barren surface of Kali was a large golden flower.

  In a brief flash of insane logic, Draker found himself racing through the sequence: (1) I’m dreaming; (2) How can I apologize to Dr. Wijeratne? (3) It doesn’t look very alien; (4) Wish I knew more about botany; (5) How nice of someone to tie an identifying label on it….

  “You bastards! You had me fooled for a minute! Was it Rani’s idea?”

  “Of course,” laughed Singh. “But as you’ll see, we’ve all signed the birthday card. And you can thank Sonny for doing such a beautiful job, out of the odd bits of paper and plastic he could find.”

  They were still chortling when they arrived back at Goliath with their amazing discovery—in much better shape, Captain Singh pointed out, than the survivors of Magellan’s crew after the circumnavigation of their world. The brief excursion had allowed them all to unwind and put aside for a moment their awesome responsibilities.

  Which was just as well: it was the last opportunity they would have to relax on Kali.

  29

  ASTROPOL

  THE DIRECTOR OF ASTROPOL HAD SEEN MUCH OF THE WORLDS and cities of Man, and considered himself incapable of being surprised. Yet now, in his elegant Geneva headquarters, he stared at his inspector general in disbelief.

  “Are you certain?” he asked.

  “Everything checks. Of course, we were suspicious—defections are very, very rare, and we wondered if it was some kind of hoax. But Deep Brain Scan confirmed it.”

  “There’s no way of fooling DBS? We’re dealing with experts.”

  “No better than ours. And the follow-up on Deimos clinches matters. We know who did the job. Of course, he’s under micro-surveillance.”

  “When will the warning get to them?”

  The inspector general glanced at his watch, which could show twenty time zones on three worlds.

  “They already have it—but they’re on the other side of the sun, and we won’t get their confirmation for another hour. I’m afraid it may be too late. If everything went on schedule, ignition was due to start forty minutes ago. There’s nothing we can do—except wait.”

  “I still can’t believe it. Why in the name of God should anyone do a thing like this?”

  “Exactly. In the name of God.”

  30

  SABOTAGE

  AT T MINUS THIRTY MINUTES GOLIATH HAD DRAWN AWAY from Kali to stand well clear of the ATLAS jet. All the systems checks had been satisfactory: now it was necessary to wait until the spin of the asteroid had brought the mass-driver around to the right position for the firing cycle to commence.

  Captain Singh and his exhausted crew did not expect to see anything spectacular: the plasma jet of the ATLAS drive would be far too hot to produce much visible radiation. Only the telemetry would confirm that ignition had started, and that Kali was no longer an implacable
juggernaut wholly beyond the control of Man.

  I wonder, thought Sir Colin Draker, how many of these youngsters know that this whole countdown idea had been invented by a German movie director almost two centuries ago, for the first space film that was not pure fantasy. Now reality had copied fiction, and it was hard to imagine any space mission starting without some human—or machine—counting backward.

  There was a brief round of cheering, and a gentle patter of applause, as the string of zeroes on the accelerometer display began to change. The feeling on the bridge was one of relief rather than exaltation. Though Kali was stirring, only sensitive instruments could detect the microscopic change in its velocity. The ATLAS drive would have to operate for days—weeks—before victory could be assured. Because of Kali’s rotation, thrust could be applied for only about ten percent of the time before ATLAS was no longer correctly aligned. It was no simple matter to steer a spinning vehicle with a fixed engine….

  One microgravity—two microgravities—sluggishly, the enormous mass of the asteroid was beginning to respond. Nobody standing on it—as far as one could stand on Kali—would have noticed the slightest change, though they might have felt a vibration underfoot, and noticed that clouds of dust were being jarred off into space. Kali was shaking itself like a dog that had just endured a bath.

  And then, unbelievably, the numbers dropped back to zero. Seconds later, three simultaneous audio alarms sounded.

  Everyone ignored them; there was nothing that could be done. All eyes were fixed on Kali—and the ATLAS booster.

  The great propellant tanks were opening up like flowers in a time-lapse movie, spilling out the thousands of tons of reaction mass that might have saved the Earth. Wisps of vapor drifted across the face of the asteroid, veiling its cratered surface with an evanescent atmosphere.

  Then Kali continued inexorably along its path.