Children of the Comet

Again, for Ann

Till a' the seas gang dry, my dear,

And the rocks melt wi' the sun.

How high can a tree on a comet grow? The answer is surprising. On any celestial body whose diameter is of the order of ten miles or less, the force of gravity is so weak that a tree can grow infinitely high. Ordinary wood is strong enough to lift its own weight to an arbitrary distance from the center of gravity. This means that from a comet of ten-mile diameter, trees can grow out for hundreds of miles, collecting the energy of sunlight from an area thousands of times as large as the area of the comet itself. Countless millions of comets are out there, amply supplied with water, carbon, and nitrogen—the basic constituents of living cells. They lack only two essential requirements for human settlement, namely warmth and air. And now biological engineering will come to our rescue. We shall learn how to grow trees on comets.

—FREEMAN DYSON

“THE WORLD, THE FLESH, AND THE DEVIL”

CHAPTER 1

6,000,000,000 A.D.

The Oort Cloud

Torris, son of Parn the Facemaker, sat a little apart from the other initiates who were waiting for their turns with Claz the Priest. It was cold where he sat, farther from the fire than he liked, with his back resting against a massive stray Tree root that had penetrated the ice cave. But his distance served to separate him from the other boys and their horseplay. As the son of Parn, he would be Facemaker himself someday, and he always had to maintain a certain distance. His father had relentlessly drilled that into him.

Claz finished with the postulant he'd been instructing. The boy rejoined the group, moving in a series of slow-motion bounces in the comet's feeble gravity. He was proudly showing off the stencil Claz had pasted to his cheek, where his mark of manhood would be etched in frostbite during the Climb ceremony.

From his priestly alcove across the ice cave, Claz signaled impatiently for the next initiate.

The noisiest of them, a boy named Brank, stood up promptly before any of the others could respond, but not so quickly that his feet lost contact with the ground. Brank was long for his age, as long as a grown man, and had sprouted a scraggly beard that brushed against the transparent Face of his hand-sewn airsuit already. Torris didn't like him very much. Brank was a brash character with a bit of a mean streak who liked to pick on the smaller boys and was known to take things that were not his.

Torris watched as Brank crossed the cavern, somehow managing to strut despite his low-gravity shuffle. But when he reached the priest's niche, he adopted a subservient posture.

Claz wasn't fooled. He gestured impatiently for Brank to kneel and peel back the hood of his airsuit.

Brank's catechism seemed to go on longer than usual. Torris couldn't make out the words from where he sat, but Brank's tone of voice seemed to grow more and more stubborn, and Claz's grew more and more angry. At last, Claz dismissed his errant postulant with a dissatisfied gesture, and when Brank joined his friends and started acting up, the priest exploded.

“What are you boys hanging around for? Those of you who are finished here, make yourselves useful! Go outside and fetch firewood! And you, Brank, you can fetch a few buckets of air to refresh the fire!”

Brank started to mutter a complaint, and Torris could make out something about “children's chores.”

Claz heard it too. “You are a child, and a useless one at that!” he snapped. “You may have the size and shape of a man, but you will not be a man until you make the Climb and bring back your Tree dream. Now go!”

Brank and a few confederates left with ill grace. The others sat, cowed for the moment. Claz's gaze lit on Torris, and he motioned him over.

Kneeling in front of Claz, his elongated legs folded under him, Torris recited the creed of the Tree. “… and we give thanks to the Tree, which clutches the world in its roots, which created man and preserves him from the dark,” he finally finished, relieved that he hadn't seriously stumbled at any of the difficult parts.

Satisfied, the old man leaned back and said, “Now, Torris, my boy, do you understand why you are making the Climb and why you must receive the mark of manhood to prove it?”

“I … I think so. It is so that I may prove myself as a man, and so that I may receive the dream the Tree gives me.”

Claz nodded his approval. “Some bring back great dreams, some little dreams or petty ones. Some, I suspect, bring back no dream at all but pretend to have received some nonsense they think will sound like a true dream. And there are always those who are afraid of the great dark and never complete the Climb, and who are known because they bring back no proof of having reached the crown, or who bring back a seed pod they've found trapped in the lower branches, or worse, stolen from another Climber—the most heinous of sins. I suspect that ne'er-do-well Brank will be one of those. But I've watched you grow up, and I expect great things from you—greater even than making Faces for the tribe like your father.”

At that point, Brank returned with a bucket of frozen air in each hand, the transparent Face of his airsuit tilted upward and covered with patches of frost. He dropped the buckets carelessly, almost contemptuously, by the fire, where they immediately started to melt and steam, making the flames flare up and turn a brighter orange. As he turned to go, he glanced over toward the priest's niche, where Claz was spreading his hands palms outward to confer his blessing. Brank's lip curled at the sight, and he shot Torris a look of sheer hatred.

CHAPTER 2

Almost the entire tribe was gathered outside the tunnel entrance to see the Climbers off. Torris estimated at least ten hands of them, not counting the babies some of the mothers were holding in translucent air sacks.

“Hold still,” his father said, checking the seams of Torris's airsuit yet again. Sounds didn't carry in the airlessness of the outside, but by necessity he was as adept as anybody else at reading lips and speaking in finger talk.

The stars were bright and fierce despite the ruddy light cast by the red star that moved. The sky was emptier of stars than it once had been, but Torris could not know that. The other two stars that moved, a white dot and an orange one that were bright enough to cast shadows, stayed aloof from the red star and rose in tandem a little afterward—or, as Claz put it, “shared the same epicycle”—adding their iota of light and heat to the bleak icescape. According to Claz, the white star and the orange one were sisters, while the big red star was a “stepsister.”

What Claz meant, no one could fathom, but he was the tribe's numberer as well as its priest and he often spoke in riddles.

Torris craned his neck to try to see the top of the Tree. But that was impossible, of course. The top was far away and hidden behind miles and miles of twisting green branches. Claz had once said that the Tree was twice as tall as the world was big around, but how anyone, even a numberer, could know such a thing was a mystery.

Still, the thought made him shiver. He was going to have to climb that unthinkable distance no matter how many turns of the world it took.

Torris tried not to show impatience as his father checked his equipment yet again. Parn carefully coiled the rope—more than ten man-lengths of it with a grappling hook at the end—and draped it across Torris's shoulder along with the stubby little bow and a quiver holding the ten bone-tipped arrows that were permitted by custom. Both the climbing rope and the bowstring were made of web beast silk rather than the animal sinews that most people used. As Facemaker, Parn would provide nothing but the best for his only son.

“Remember,” he said behind his faceplate with the exaggerated lip movements of no-air talk, “there are two kinds of web beasts: those that use their silk to spin webs for catching, and those that hunt and spin silk ropes to anchor themselves when they swing at their prey. If you're careless enough to get caught in a web and a web spinner starts toward you, don't try to use your bow. You won't be fast enough. Use your spear. Thrust, don't throw. Aim for the center of the cluster of eyes. And don't let go of the spear. That way you'll be able to hold it off while it's dying.”

“Yes, Father.”

“On the other hand, if you're being stalked by one of the hunting variety and you see it start its swing toward you, you'll have all the time in the world to nock an arrow, aim, and send it through the creature. It's just a question of keeping your head. You have to calculate the angle of the swing and the length and timing of the arc as it keeps lengthening. Your brain will do all that for you without your thinking about it, as long as you don't panic. Remember that the creature is helpless while it's dangling, and that the force of the arrow will spoil its own timing, so when it drops it won't land on top of you if you stay alert. Their poison is dangerous even when they're dead. Can you remember all that?”

He waited for a reply, his expression stern.

Torris tried to make his nod look earnest. He'd heard it all a thousand times while he was growing up.

“As for flutterers and tree snakes and other such creatures, there's no single formula for dealing with them. You've been on meatbeast hunts with me and the other men, and you know what to expect.”

He held Torris at arm's length and looked him over with a nod of approval. The flawless new airsuit had been sewn together out of everted meatbeast gut by Firstmother. It would probably be the last one he'd need. She'd sighed when she'd fitted it to him. “You've stopped growing, Torris,” she'd said. “Your last suit was getting much too tight, and perhaps I waited too long, but I wanted to be sure.”

And now, seeing that Parn was through with him, she came diffidently forward and gave him a farewell hug. “Be careful, my precious Torris, and may the God-Tree protect you,” she said in voicetalk, her faceplate touching his, sounding thin and faint through the resin mask but still understandable. She'd wanted her words to be private, not to be read by others.

She released him and stepped aside so Secondmother could say goodbye. Secondmother was hardly older than Torris himself, and she was big with child. She smiled, too shy to speak, and handed him the caddy of food she'd prepared for the breaking of his fast.

Parn stepped in again. “Don't gobble up your climbfeast as soon as you're out of sight of the ground, as some of those whelps will do,” he said. “Remember that your fast still has a day to go. And try to save a little. After you've had your climbfeast you'll have to rely on what you can hunt or forage, and you might not get lucky right away.”

Torris nodded, but he had stopped paying attention. He was lightheaded from two days of fasting, but he was too eager to get started to think about being hungry. He wished his father would stop talking so that he could join the straggling group of Climbers who were starting to assemble.

But his father wasn't finished with him. Torris tried to look as if he were listening. He understood that his father probably was trying to hang on to these last moments as long as possible.

“And remember,” Parn droned silently on in finger talk, “no matter how hungry you get, your first priority is to capture a stovebeast. The heatholder in your suit is only good for a day at best. The Tree is full of the picked skeletons of those who valued their stomachs more than their warmth.”

Over by the gnarled slope of the Tree's base, Claz was getting ready for the final benediction, and the Climbers were gathering in a ragged semicircle around him. But Parn's only concession was to hurry his words a little. “… and the three airskins that a Climber is allowed won't last forever either. Replenish them as you go along, and never allow yourself more than one empty. Two empties and you're in trouble. The best place to drill a vent is …” It was too much. Even Parn realized it, and he broke off abruptly.

Torris moved his lips in a hasty goodbye and bounded off in an alarming series of high-flying arcs.

Claz was being mercifully brief. The Climb ceremony was in its third day, and there was nothing left to say. He gave a final blessing, making the ritual gestures that had been passed down by priests through the ages, symbolizing the sweeping arc of the triple stars with a swoop of his right hand and sketching their intricate dance with a wiggle of fingers.

Torris dutifully gave the proper responses and wished fervently that he could scratch the frostbitten itch under the stencil.

The Climbers chose their routes and spread out along the base of the Tree. Each Climber had to make his journey alone. It was forbidden to receive or give help to another Climber, or even approach him if your paths happened to cross.

Torris had already picked his spot—a gnarled channel that rose straight up and disappeared into the lower branches and that was narrow enough to afford a purchase on either side. Some of the boys looked for knobby projections or other random handholds, but a long groove like the one he'd chosen was better, giving you an uninterrupted head start.

He looked around at his fellow Climbers. A few of them had already started up the trunk. Far down the line, almost where the curve of the enormous base of the Tree cut off his view, he saw Brank, who seemed to be checking out the Climbers on either side of him but making no effort to start his own Climb. If his gaze had lit on Torris, he was too far away to tell. But abruptly he sprang for the Tree, slamming into it about three man-lengths up, where there was nothing to grab hold of. The slow rotation of the world was starting to make him float slowly toward the outer darkness, but while he was still within arm's length of the trunk, he made a grab for his knife and stabbed it violently into the bark. It held, leaving him hanging, legs streaming outward.

Torris was appalled at the stupidity of Brank's gamble. If the blade had hit a hard spot or hadn't penetrated deeply enough to hold, the recoil from the blow would have propelled Brank irrevocably into the black sky, and not one of the men watching from below would have lifted a finger to save him. Brank's contact with the Tree had given him a Climber's untouchability, and it was forbidden to help him. It was a wise taboo; it helped the tribe shed its inept members before they could weaken it with their seed.

Torris did not wait to see how Brank continued his Climb. He centered himself in the groove, made a quick calculation, and leaped upward, his legs dangling free and his long arms hanging at his sides. His leap had carried him up about five man-lengths, and before he could drift out of reach, he pressed his palms against the walls of the niche on either side. He weighed only a few ounces, and the slight pressure was enough to hold him in place. He started to climb, using just his hands and letting his legs hang free. He didn't need legs at this stage, and it was quicker to pull himself along by hand.

He found his first stovebeast before the Tree turned nightward. It was wedged in a crook between the trunk and one of the massive branches, where it could quietly lap up the insects and other small prey that were attracted by its heat. It was about the size of a grown person's head, a furry round ball with four vestigial limbs that were good for nothing but clinging.

He pried it loose and dropped it in his backpack, letting his other one go. He could feel it immediately trying to attach itself to the inner surface next to his back, its life-giving warmth starting to spread through his suit. It would be good for a few days without being fed, and he could turn it loose when he found another firebelly to replace it.

They were not good to eat, though there were those who had to learn that the hard way. If you cut a stovebeast open, there was no actual fire inside, only a flood of noxious fluids that combined somehow to produce that flameless heat.

Torris resumed his Climb. The tunnel entrances to the tribe's cave were far out of sight between the twisting branches. He had some distance to go before he allowed himself to find a nest for the night. He could see how the Tree's leaves had turned almost edge-on to catch the last vestiges of the red star's heat. Claz said that the Trees used the pressure of starlight, if there was such a thing, to hunt down fresh comets to snare in their roots whenever they sucked the old ones dry. But that was just legend.

Still, one often saw a distant Tree floating free in space without an iceball or clutching an iceball that was shrunken to almost nothing so that it showed a ball of bare roots that were beginning to turn green to catch starlight. One wondered what other tribes did on such worlds. Did they hollow out caves in the God-Tree itself? Live in the branches? Or did they migrate to another God-Tree that might have drifted close enough? If so, the whole tribe would have to make that dangerous leap, not just the intrepid young men who launched themselves into the dark on bride raids whenever the opportunity presented itself.

Torris was feeling hunger now, but he resolved to wait out his fast till morning. He concentrated on climbing and looking out for predators. He was high enough to be in wild territory now, beyond the tribe's traditional hunting grounds. The more dangerous beasts had not been hunted out here.

Another hour of climbing and he flushed a covey of treehoppers that darted off in all directions. They were four-legged, like most life found in the Tree, with long, prehensile bushy tails. The little creatures somehow never seemed to launch themselves inadvertently into open space; here in the thick of the branches, they almost always managed to fetch up against a twig or cluster of leaves. He didn't bother to chase after any of them with net and spear. Tomorrow would be soon enough.

He was high enough, and he was getting drowsy. He found a sheltered spot in the lee of a branch and laid out his climbing kit. With a bone awl, he tapped into the Tree's vascular system and at first found only the thin clear resin that his father used to cast faceplates. He drilled deeper into the cambium and obtained a trickle of the watery sweet fluid that was good to drink. He filled a couple of small skins with this. Finally his persistence was rewarded with a gush of air from a cavity where it had collected. He used it to replenish the depleted air sack, adding the airflow to the remaining slush, where, increment by increment, it became slush itself. It took a long time, and when the frozen air had lost the ability to add to itself, he channeled the airstream directly into his sleeping sack through a tube made of meatbeast gut.

That done, he crawled into his sleeping sack, sealed its neck around the improvised breathing tube, and raised his faceplate to inhale the Tree's gift of air. It had a pleasant resinous smell like carpentered wood. He yawned and dropped off to sleep, the comforting warmth of the stovebeast pressed against his back.