Vacuum Diagrams

by Stephen Baxter

  Leaning closer, Larionova saw that tendrils from the wormthing had even infiltrated the brain-tubes. She shuddered; if this was a parasite, it was a particularly vile infestation. Maybe the parasite even modified the mercuric's behavior, she wondered.

  Dixon restored the solid-aspect Virtual.

  Uneasily, Larionova pointed to the markings on the carapace. They were small triangles, clustered into elaborate patterns. "And what's this stuff?"

  Dixon hesitated. "I was afraid you might ask that."

  "Well?"

  "...We think the markings are artificial, Irina. A deliberate tattoo, carved into the carapace, probably with the mandibles. Writing, maybe: those look like symbolic markings, with information content."

  "Lethe," she said.

  "I know. This fish was smart," Dixon said.

  The people, victorious, clustered around the warmth of their new Chimney. Recovering from their journey and from their battle-wounds, they cruised easily over the gardens of cilia-plants, and browsed on floating fragments of food.

  It had been a great triumph. The Heads were dead, or driven off into the labyrinth of tunnels through the Ice. Strong-Flukes had even found the Heads' principal nest here, under the silty floor of the cavern. With sharp stabs of her mandibles, Strong-Flukes had destroyed a dozen or more Head young.

  Cilia-of-Gold took herself off, away from the Chimney. She prowled the edge of the Ice cavern, feeding fitfully.

  She was a hero. But she couldn't bear the attention of others: their praise, the warmth of their bodies. All she seemed to desire now was the uncomplicated, silent coolness of Ice.

  She brooded on the infestation that was spreading through her.

  Seekers were a mystery. Nobody knew why Seekers compelled their hosts to isolate themselves, to bury themselves in the Ice. What was the point? When the hosts were destroyed, so were the Seekers.

  Perhaps it wasn't the Ice itself the Seekers desired, she wondered. Perhaps they sought, in their blind way, something beyond the Ice...

  But there was nothing above the Ice. The caverns were hollows in an infinite, eternal Universe of Ice. Cilia-of-Gold, with a shudder, imagined herself burrowing, chewing her way into the endless Ice, upwards without limit... Was that, finally, how her life would end?

  She hated the Seeker within her. She hated her body, for betraying her in this way; and she hated herself.

  "Cilia-of-Gold."

  She turned, startled, and closed her carapace around herself reflexively.

  It was Strong-Flukes and Ice-Born, together. Seeing their warm, familiar bodies, here in this desolate corner of the cavern, Cilia-of-Gold's loneliness welled up inside her, like a Chimney of emotion.

  But she swam away from her Three-mates, backwards, her carapace scraping on the cavern's Ice wall.

  Ice-Born came towards her, hesitantly. "We're concerned about you."

  "Then don't be," she snapped. "Go back to the Chimney, and leave me here."

  "No," Strong-Flukes said quietly.

  Cilia-of-Gold felt desperate, angry, confined. "You know what's wrong with me, Strong-Flukes. I have a Seeker. It's going to kill me. And there's nothing any of us can do about it."

  Their bodies pressed close around her now; she longed to open up her carapace to them and bury herself in their warmth.

  "We know we're going to lose you, Cilia-of-Gold," Ice-Born said. It sounded as if she could barely speak. Ice-Born had always been the softest, the most loving, of the Three, Cilia-of-Gold thought, the warm heart of their relationship. "And—"

  "Yes?"

  Strong-Flukes opened her carapace wide. "We want to be Three again," she said.

  Already, Cilia-of-Gold saw with a surge of love and excitement, Strong-Flukes's ovipositor was distended: swollen with one of the three isogametes which would fuse to form a new child, their fourth...

  A child Cilia-of-Gold could never see growing to consciousness.

  "No!" Her cilia pulsed with the single, agonized word.

  Suddenly the warmth of her Three-mates was confining, claustrophobic. She had to get away from this prison of flesh; her mind was filled with visions of the coolness and purity of Ice: of clean, high Ice.

  "Cilia-of-Gold. Wait. Please—"

  She flung herself away, along the wall. She came to a tunnel mouth, and she plunged into it, relishing the tunnel's cold, stagnant water.

  "Cilia-of-Gold! Cilia-of-Gold!"

  She hurled her body through the web of tunnels, carelessly colliding with walls of Ice so hard that she could feel her carapace splinter. On and on she swam, until the voices of her Three-mates were lost forever.

  We've dug out a large part of the artifact, Irina, Dolores Wu reported. It's a mass of what looks like hull material.

  "Did you get a sample?"

  No. We don't have anything that could cut through material so dense... Irina, we're looking at something beyond our understanding.

  Larionova sighed. "Just tell me, Dolores," she told Wu's data-desk image.

  Irina, we think we're dealing with the Pauli Principle.

  Pauli's Exclusion Principle stated that no two fermions — electrons or quarks — could exist in the same quantum state. Only a certain number of electrons, for example, could share a given energy level in an atom. Adding more electrons caused complex shells of charge to build up around the atom's nucleus. It was the electron shells — this consequence of Pauli — that gave the atom its chemical properties.

  But the Pauli Principle didn't apply to photons; it was possible for many photons to share the same quantum state. That was the essence of the laser: billions of photons, coherent, sharing the same quantum properties.

  Irina, Wu said slowly, what would happen if you could turn off the Exclusion Principle, for a piece of fermionic matter?

  "You can't," Larionova said immediately.

  Of course not. Try to imagine anyway.

  Larionova frowned. What if one could lase mass? "The atomic electron shells would implode, of course."

  Yes.

  "All electrons would fall into their ground state. Chemistry would be impossible."

  Yes. But you may not care...

  "Molecules would collapse. Atoms would fall into each other, releasing immense quantities of binding energy."

  You'd end up with a super dense substance, wouldn't you? Completely non-reactive, chemically. And almost unbreachable, given the huge energies required to detach non-Pauli atoms.

  Ideal hull material, Irina...

  "But it's all impossible," Larionova said weakly. "You can't violate Pauli."

  Of course you can't, Dolores Wu replied.

  Inside an opaqued bubble-shelter, Larionova, Dixon and Scholes sat on fold-out chairs, cradling coffees.

  "If your mercuric was so smart," Larionova said to Dixon, "how come he got himself stuck in the ice?"

  Dixon shrugged. "In fact it goes deeper than that. It looked to us as if the mercuric burrowed his way up into the ice, deliberately. What kind of evolutionary advantage could there be in behavior like that? The mercuric was certain to be killed."

  "Yes," Larionova said. She massaged her temples, thinking about the mercuric's infection. "But maybe that thread-parasite had something to do with it. I mean, some parasites change the way their hosts behave."

  Scholes tapped at a data desk; text and images, reflected from the desk, flickered over his face. "That's true. There are parasites which transfer themselves from one host to another — by forcing a primary host to get itself eaten by the second."

  Dixon's wide face crumpled. "Lethe. That's disgusting."

  "The lancet fluke," Scholes read slowly, "is a parasite of some species of ant. The fluke can make its host climb to the top of a grass stem and then lock onto the stem with its mandibles — and wait until it's swallowed by a grazing sheep. Then the fluke can go on to infest the sheep in turn."

  "Okay," Dixon said. "But why would a parasite force its mercuric host to burrow up into the ice of a frozen ocean? When
the host dies, the parasite dies, too. It doesn't make sense."

  "There's a lot about this that doesn't make sense," Larionova said. "Like, the whole question of the existence of life in the cavities in the first place. There's no light down there. How do the mercurics survive, under two miles of ice?"

  Scholes folded one leg on top of the other and scratched his ankle. "I've been going through the data desks." He grimaced, self-deprecating. "A crash course in exotic biology. You want my theory?"

  "Go ahead."

  "The thermal vents — which cause the cavities in the first place. The vents are the key. I think the bottom of the Chao ice-cap is like the mid-Atlantic ridge, back on Earth.

  "The deep sea, a mile down, is a desert; by the time any particle of food has drifted down from the richer waters above it's passed through so many guts that its energy content is exhausted.

  "But along the Ridge, where tectonic plates are colliding, you have hydrothermal vents — just as at the bottom of Chao. And the heat from the Atlantic vents supports life: in little colonies, strung out along the mid-Atlantic Ridge. The vents form superheated fountains, smoking with deep-crust minerals which life can exploit: sulphides of copper, zinc, lead and iron, for instance. And there are very steep temperature differences, and so there are high energy gradients — another prerequisite for life."

  "Hmm." Larionova closed her eyes and tried to picture it. Pockets of warm water, deep in the ice of Mercury; luxuriant mats of life surrounding mineral-rich hydrothermal vents, browsed by Dixon's mercuric animals... was it possible?

  Dixon asked, "How long do the vents persist?"

  "On Earth, in the Ridge, a couple of decades. Here we don't know."

  "What happens when a vent dies?" Larionova asked. "That's the end of your pocket world, isn't it? The ice chamber would simply freeze up."

  "Maybe," Scholes said. "But the vents would occur in rows, along the scarps. Maybe there are corridors of liquid water, within the ice, along which mercurics could migrate."

  Larionova thought about that for a while.

  "I don't believe it," she said.

  "Why not?"

  "I don't see how it's possible for life to have evolved here in the first place." In the primeval oceans of Earth, there had been complex chemicals, and electrical storms, and...

  "Oh, I don't think that's a problem," Scholes said.

  She looked at him sharply. Maddeningly, he was grinning again. "Well?" she snapped.

  "Look," Scholes said with grating patience, "we've two anomalies on Mercury: the life-forms here at the South Pole, and Dolores Wu's artifact under Caloris. The simplest assumption is that the two anomalies are connected. Let's put the pieces together," he said. "Let's construct a hypothesis..."

  Her mandibles ached as she crushed the gritty Ice, carving out her tunnel upwards. The rough walls of the tunnel scraped against her carapace, and she pushed Ice rubble down between her body and her carapace, sacrificing fragile cilia designed to extract soft food particles from warm streams.

  The higher she climbed, the harder the Ice became. The Ice was now so cold she was beyond cold; she couldn't even feel the Ice fragments that scraped along her belly and flukes. And, she suspected, the tunnel behind her was no longer open but had refrozen, sealing her here, in this shifting cage, forever. The world she had left — of caverns, and Chimneys, and children, and her Three-mates — were remote bubbles of warmth, a distant dream. The only reality was the hard Ice in her mandibles, and the Seeker heavy and questing inside her.

  She could feel her strength seeping out with the last of her warmth into the Ice's infinite extent. And yet still the Seeker wasn't satisfied; still she had to climb, on and up, into the endless darkness of the Ice.

  ...But now — impossibly — there was something above her, breaking through the Ice...

  She cowered inside her Ice-prison.

  Kevan Scholes said, "Five billion years ago — when the Solar System was very young, and the crusts of Earth and other inner planets were still subject to bombardment from stray planetesimals — a ship came here. An interstellar craft, maybe with FTL technology."

  "Why? Where from?" Larionova asked.

  "I don't know. How could I know that? But the ship must have been massive — with the bulk of a planetesimal, or more. Certainly highly advanced, with a hull composed of Dolores' super dense Pauli construction material."

  "Hmm. Go on."

  "Then the ship hit trouble."

  "What kind of trouble?"

  "I don't know. Come on, Dr. Larionova. Maybe it got hit by a planetesimal itself. Anyway, the ship crashed here, on Mercury—"

  "Right." Dixon nodded, gazing at Scholes hungrily; the American reminded Larionova of a child enthralled by a story. "It was a disastrous impact. It caused the Caloris feature..."

  "Oh, be serious," Larionova said.

  Dixon looked at her. "Caloris was a pretty unique impact, Irina. Extraordinarily violent, even by the standards of the System's early bombardment phase... Caloris Basin is eight hundred miles across; on Earth, its walls would stretch from New York to Chicago."

  "So how did anything survive?"

  Scholes shrugged. "Maybe the starfarers had some kind of inertial shielding. How can we know? Anyway the ship was wrecked; and the density of the smashed-up hull material caused it to sink into the bulk of the planet, through the Caloris puncture.

  "The crew were stranded. So they sought a place to survive. Here, on Mercury."

  "I get it," Dixon said. "The only viable environment, long term, was the Chao Meng-Fu ice cap."

  Scholes spread his hands. "Maybe the starfarers had to engineer descendants, quite unlike the original crew, to survive in such conditions. And perhaps they had to do a little planetary engineering too; they may have had to initiate some of the hydrothermal vents which created the enclosed liquid-water world down there. And so—"

  "Yes?"

  "And so the creature we've dug out of the ice is a degenerate descendant of those ancient star travelers, still swimming around the Chao Sea."

  Scholes fell silent, his eyes on Larionova.

  Larionova stared into her coffee. "A 'degenerate descendant.' After five billion years? Look, Scholes, on Earth it's only three and a half billion years since the first prokaryotic cells. And on Earth, whole phyla — groups of species — have emerged or declined over periods less than a tenth of the time since the Caloris Basin event. Over time intervals like that, the morphology of species flows like hot plastic. So how is it possible for these mercurics to have persisted?"

  Scholes looked uncertain. "Maybe they've suffered massive evolutionary changes," he said. "But we're just not recognizing them. For example, maybe the worm parasite is the malevolent descendant of some harmless creature the starfarers brought with them."

  Dixon scratched his neck, where the suit-collar ring of dirt was prominent. "Anyway, we've still got the puzzle of the mercuric's burrowing into the ice."

  "Hmm." Scholes sipped his cooling coffee. "I've got a theory about that, too."

  "I thought you might," Larionova said sourly.

  Scholes said, "I wonder if the impulse to climb up to the surface is some kind of residual yearning for the stars."

  "What?"

  Scholes looked embarrassed, but he pressed on: "A racial memory buried deep, prompting the mercurics to seek their lost home world... why not?"

  Larionova snorted. "You're a romantic, Kevan Scholes."

  A telltale flashed on the surface of the data desk. Dixon leaned over, tapped the telltale and took the call.

  He looked up at Larionova, his moonlike face animated. "Irina. They've found another mercuric," he said.

  "Is it intact?"

  "More than that." Dixon stood and reached for his helmet. "This one isn't dead yet..."

  The mercuric lay on Chao's dust-coated ice. Humans stood around it, suited, their face plates anonymously blank.

  The mercuric, dying, was a cone of bruised-purple meat a yard lon
g. Shards of shattered transparent carapace had been crushed into its crystallizing flesh. Some of the cilia, within the carapace, stretched and twitched. The cilia looked differently colored to Dixon's reconstruction, as far as Larionova could remember: these were yellowish threads, almost golden.

  Dixon spoke quickly to his team, then joined Larionova and Scholes. "We couldn't have saved it. It was in distress as soon as our core broke through into its tunnel. I guess it couldn't take the pressure and temperature differentials. Its internal organs seem to be massively disrupted..."

  "Just think." Kevan Scholes stood beside Dixon, his hands clasped behind his back. "There must be millions of these animals in the ice under our feet, embedded in their pointless little chambers. Surely none of them could dig more than a hundred yards or so up from the liquid layer."

  Larionova switched their voices out of her consciousness. She knelt down, on the ice; under her knees she could feel the criss-cross heating elements in her suit's fabric.

  She peered into the dulling sonar-eyes of the mercuric. The creature's mandibles — prominent and sharp — opened and closed, in vacuum silence.

  She felt an impulse to reach out her gloved hand to the battered flank of the creature: to touch this animal, this person, whose species had, perhaps, traveled across light years — and five billion years — to reach her...

  But still, she had the nagging feeling that something was wrong with Scholes' neat hypothesis. The mercuric's physical design seemed crude. Could this really have been a starfaring species? The builders of the ship in Caloris must have had some form of major tool-wielding capability. And Dixon's earlier study had shown that the creature had no trace of any limbs, even vestigially...

  Vestigial limbs, she remembered. Lethe.

  Abruptly her perception of this animal — and its host parasite — began to shift; she could feel a paradigm dissolving inside her, melting like a Mercury snowflake in the Sun.

  "Dr. Larionova? Are you all right?"