Space m-2

by Stephen Baxter

  This was a world of volcanism. The vast plains were covered by flood basalts — frozen lakes of lava, like the maria of the Moon — and punctured by thousands of small volcanoes, shield-shaped, built up by repeated outpourings of lava. But there were some shield structures — like the Hawaiian volcanoes, like Maat Mons — that towered five or eight kilometers above the plains, covered in repeated lava flows.

  As she drifted farther east, away from Aphrodite and over a smooth basalt lowland, Carole learned to pick out features that had no counterparts on Earth. There were steep-sided, flat-topped domes formed by sticky lava welling up through flaws in the crust. There were volcanoes with their flanks gouged away by huge landslides that left ridges like protruding insect legs. There were domes surrounded by spiderweb patterns of fractures and ridges. There were volcanoes with flows that looked like petals, pushing out across the plains.

  And, most spectacular, there were coronae: utterly unearthly, rings of ridges and fractures. Some of these were thousands of kilometers across, giant features each big enough to straddle much of the continental United States. Perhaps they were formed by blobs of upwelling magma that pushed up the crust and then spread out, allowing the center to implode, like a failed cake. To Carole the rings of swollen, distorted, and broken crust looked like the outbreak of some immense chthonic mold from Venus’s deep interior.

  There were even rivers here.

  Her balloon ship drifted over valleys kilometers wide and thousands of kilometers in length, unlikely Amazons complete with flood plains, deltas, meanders, and bars, here on a world where no liquid water could have flowed for billions of years — if ever. One of these, called Baltis Vallis, was longer than the Nile, and so it was the longest river valley in the Solar System. Perhaps the rivers had been cut by an exotic form of lava — for example, formed by a salty carbon-rich rock called carbonatite — that might have flowed in Venus’s still-hotter past.

  Suspended from a balloon, Carole would drift over this naked world for a week while her eyes and the lander’s sensors probed at the strange landscapes below. And then, perhaps, she would land.

  She was, despite herself, enchanted. Venus had no water, no life; and yet it was a garden, she saw: a garden of volcanism and sculptured rock. My mother would have understood all this, Carole thought with an echo of her old, lingering guilt. But my mother isn’t here. I’m here.

  But Nemoto, coldly, told her to look for patterns. “You are not a tourist. Look beyond the spectacle, Carole. What do you see?”

  What Carole saw was wrinkles and craters.

  Wrinkles: the ground was covered with ridges and cracks, some of them running hundreds of kilometers, as if the whole planet were an apricot left too long in the Sun.

  And craters: they were everywhere, hundreds of them, spread evenly over the whole of the planet’s surface. There were few very large craters — and few very small ones too; hardly any less than five or ten kilometers across.

  “…Violence, you see,” Nemoto said. “Global violence. Those wrinkles in the lowlands, like the tesserae cracks of the highlands, are proof that the whole of the lithosphere, the outer crust of this planet, was stretched or compressed — all at the same time. What could do such a thing?

  “And as for the craters, there is little wind erosion here, Carole; the air at the bottom of this turgid ocean of gas is very still, and so the craters have remained as fresh as when they were formed. Few are small, for that thick air screens out the smaller impactors, destroying them before they reach the ground. But, conversely, few of the craters are large. Certainly none of them compare with the giant basins of the Moon. But those immense lunar basins date back to the earliest days of the Solar System, when the sky was still full of giant rogue planetesimals. And so we can tell, you see—”

  “ — that these craters are all young,” Carole said.

  “ — that no crater is much older than eight hundred million years,” Nemoto said, not yet hearing her. “In fact, no feature on the surface of this planet appears older than that. Eight hundred million years: it might seem an immense age to you, but the planets are five times older still. Carole, eight hundred million years ago, something happened to Venus — something that distorted the entire surface, wiping it clean of older features, destroying four billion years of geologic heritage. We can never know what was lost, what traces of continents and seas were brutally melted…”

  Eight hundred million years, Carole thought. The same age as the moonlet artifacts. That was the significance Nemoto saw. Her skin prickled.

  What had been done to Venus, eight hundred million years ago?

  She drifted into the planet’s long night. But there was no relief from the searing warmth, so effectively did the great blanket of air redistribute the heat; at midnight the air was only a few degrees cooler than at noon.

  Nemoto’s automated probes, she learned, had found life on Venus, here on this baked, still planet.

  Or rather, traces of life.

  Like the heat-loving microbes of Earth’s deep ocean vents, these had been creatures that had once swum in a hot, salty ocean of water. Carole learned that human scientists had long expected to find such organisms here: organisms that must now be extinct everywhere, their potential lost forever, destroyed by the planet’s catastrophic heating. Nothing left but microscopic fossils in the oldest rocks…

  The sky wound down through degrees of deepening crimson. As her eyes adapted to the dark, she saw that there was still light here — but no starlight could penetrate the immense column of air above. The ground itself was shining: she saw wrinkles and ridges and volcanic cones looming eerily from the dark.

  On Venus, even at night, the rock was so hot it glowed.

  But this faint illumination did not seem hellish. It was as if she were drifting over a fairyland, a land halfway to unreality; and the inversion of her perspective — darkness above, light below — seemed very strange.

  When she reached the dawn terminator, there was a slow and subtle change, of ground glow to sky shine, and the world became normal once more.

  Nemoto told her to prepare for landing. Nemoto’s agitated excitement was obvious. She directed Carole to head for the mountains. Through her automated probes, Nemoto had found something, a worthy target for their one-and-only attempt at landing.

  Ishtar Terra was a continent the size of Australia, rising high above the global plains. Carole drifted in from the west, over a plateau called Lakshmi Planum: twice the size of Tibet, a place of huge volcanic outflows. The perimeter of the Planum was composed of rough mountain ranges — long, curved ridges with deep troughs between, terrain that reminded her of the Appalachians seen from the air. And its southern perimeter was a huge clifflike feature: three kilometers high, sloping at more than twenty degrees, its great flanks littered by landslides.

  To the east the ground began to rise up toward the immense, towering mountain range called Maxwell Montes. She drifted south over one great summit. It was eleven kilometers tall, one and a half times as tall as Everest, and with a giant impact crater punched into its flank. She descended toward the southwestern corner of the massif.

  The landing was gentle, flawless.

  The first human on Venus. Mom, you should see me now.

  Carole stepped forward, picking her way between loose plates of rock. There was no wind noise. But when her metal-booted feet crunched on loose rock, the noise was very sharp and piercing; sound, it seemed, would carry a long way in this dense, springy air.

  The world was red.

  The sky was tall above her, a vast diffuse dome of dull, oppressive red. The air was thick — it resisted her motions, like a fluid, as if she were immersed in some sea — but it was clear, and still. The rocks were crimson plates. There seemed to be some kind of frost on them; here and there they sparkled, dully. Now, how could that be?

  She walked forward. She tried to describe the ground, to be a geologist.

  “The plain has many fine features: honeycombs,
small ridges, fissures. It is littered with flat plates of rock, one or two meters wide. It is like a flat, rocky desert on Earth.” She knelt to inspect a rock more closely; exoskeletal multipliers prodded her limbs, helping her position her heavy suit. “I can see strata in this rock. It looks like a terrestrial volcanic rock, perhaps a gabbro, but it seems to have been formed by multiple lava flows, over time. The rock is speckled by dark spots. They seem to be erosionpits. They are filled with soil. There is something like frost glittering, a very fine shimmer, clusters of crystals.” She had a lab unit. She pressed it against the surface of a rock, being sure she caught a little of that strange layer of frost.

  Cautiously, with a hand encased in an articulated tungsten glove like a claw, she reached out to touch the rock. That frosty layer scraped away; it was clearly very thin. Of course it couldn’t be water-ice frost. What, then?

  At her gentle prod, a section of the rock the size of her hand broke away along a plane and crumbled to dust and fragments that sank slowly to the ground.

  She straightened up. Experimentally she raised one foot and stepped up onto a rock. It crumbled like a meringue, breaking along cracks that ran deep into the rock’s fabric.

  This was chemical weathering. There was no water here to wash away the rocks, no rain to drench them, no frost to crack them, no strong winds to batter them with sand. But the dense, corrosive atmosphere worked its way into the fine structure of the rocks, eating them away from the inside. All over Venus, she thought, the rocks must simply be rotting in place, waiting for a nudge to crumble and fall.

  She looked around.

  She was standing on a plateau, here in the Maxwell Montes. To her south, no more than a kilometer away, a steep cliff led down to the deeper plains. To the north — beyond the squat lander on its sturdy legs — she could see the great shadowy bulks of the mountains, cones of a deeper crimson painted against the red sky.

  She had landed some five kilometers above the mean level — there was no sea level on Venus, with no seas. Here, in the balmy heights of Ishtar Terra, it was some forty degrees cooler than on the great volcanic plains — though, at more than four hundred degrees centigrade, that was little help to her equipment — and the air pressure was only a third of its peak value, on the lowest plains. But this was nearly as deep into Venus’s air ocean as she could go.

  Still, her suit was a monstrous shell of tungsten, more like a deep-sea diver’s suit than a space suit. On her back and chest she wore packs laden with consumables and heat exchangers, sufficient to keep her alive for a few hours. But, like her ship, her key piece of refrigeration technology was a set of lasers that periodically dumped her excess heat into the Venusian rock. The suit was ingenious, but hardly comfortable; Venus’s gravity was 90 percent of Earth’s, and the suit was heavy and confining.

  She tilted back and looked up into the sky.

  She couldn’t see the Sun; the dim, crimson light was uniform, thoroughly scattered, apparently without a source. But the sky was not featureless. She could see through the lower air and the haze to those great cloud decks, all of fifty kilometers above. There were holes in the clouds, patches of brighter sky, making it a great uneven sheet of light. And the patches were moving. The sky was full of giant shifting shapes of light and darkness, slowly forming and dissolving, like fragments of a nightmare. The flow was stately, silent, a sign of huge stratospheric violence far removed from the still, windless pool of air in which she stood.

  Astonishing, beautiful. And nobody in all human history had seen this before her.

  “I’ve analyzed your frost,” Nemoto said evenly. “It’s tellurium. Almost pure metal. On Venus, tellurium would vaporize at lower altitudes. So it has snowed out here, just as water snows out at the peaks of our own mountains.”

  A snow of metal. How remarkable, Carole thought.

  “Now,” Nemoto said slyly, “tellurium is rare. It makes up only one-billionth of one percent of our surface rocks, and we’ve no reason to believe the rocks of Venus differ so significantly. But tellurium, for a technological society, is useful stuff. We use it to improve stainless steel, and in electrolysis, and in electronics, and as a catalyst in refining petroleum. How did so much tellurium, such an exotic high-tech material, get deposited on Venus?”

  Not by the natives, Carole thought, those wretched long-extinct bacteria. Visitors. Those who came here before us, before the Gaijin, long before. Perhaps they were the acid-breathers who built the moonlets. Perhaps they crashed here, and the tellurium was a relic of their ship: all that remains of them after eight hundred million years — a thin metallic frost on the mountains of Venus.

  There was a sudden flash, far above. Many minutes later, she heard what sounded like thunder. Giant electrical storms raged in those high clouds. But there was no rain, of course.

  She watched the clouds, entranced.

  She walked steadily forward, heading southwest, away from the lander. Soon she was approaching the lip of the plateau. She could see no land beyond; evidently the drop-off was steep.

  “Let me tell you what I believe,” Nemoto whispered. “When Venus formed, it was indeed a twin of Earth. I believe Venus rotated quickly, much as Earth does, as Mars does, taking no more than a few Earth days to spin on its axis; why should Venus have been different? I believe Venus was formed with a moon, like Earth’s. And I believe it had oceans, of liquid water. There is no reason why Venus should not have formed with as much water as Earth. There were oceans, and tides…”

  With surprising suddenness, Carole came to the edge.

  A cliff face fell away before her, marked here and there by the lobed flow of landslides. This great ridge ran for kilometers to either side, all the way to the horizon and beyond. And the slope continued down — on and on, down and down, as if she were looking over the edge of a continental shelf into some deeper ocean — until it merged with a plateau, far below, and then the planet-circling volcanic plain beyond that.

  This was the edge of the Maxwell mountains region. This cliff descended six kilometers in just eight kilometers’ distance, an average slope of thirty-five degrees. There was nothing like it on Earth, anywhere.

  She had to descend to the level of the Lakshmi Planum, six kilometers below, to study Nemoto’s puzzle. They hadn’t anticipated any surface journey of such length and difficulty; she hadn’t brought a surface vehicle, and the lander had neither the fuel nor the capability to fly her deeper into the ocean of air. And so she had to walk.

  Nemoto had said she owed it to the human race to accept the risk, to complete her mission. Carole just thought she owed it to her mother, who would surely not have hesitated.

  “Of course Venus is closer to the Sun; even wet, Venus was not an identical twin of Earth. The air was dominated by carbon dioxide. The oceans were hot — perhaps as hot as two hundred degrees — and the atmosphere humid, laden with clouds. But, thanks to the water, plate tectonics operated, and much of the carbon dioxide was kept locked up in the carbonate rocks, which were periodically subducted into the mantle, just as on Earth.

  “Venus was a moist greenhouse, where life flourished…”

  She found talus slopes, rubble left by crumbled rocks. It would require care, but this type of climb wasn’t so unfamiliar to Carole. She had hiked in places in the Rocky Mountains that were rather like this, places where chemical weathering seemed to dominate, even on Earth. But the depth would push the envelope of her suit’s design. And, of course, there was nobody here to help her up. So she took care not to fall.

  After a couple of kilometers she paused for breath. She looked down, across kilometers of steeply sloping rock, to the Planum below.

  She thought she could see something new, emerging from the murk: a long dark line, oddly straight, that disappeared here and there among folds in the rock, only to emerge once more farther along. As if somebody had reached down with a straightedge and scoured a deep dark cut into these hot rocks.

  There was something beside the line, squat an
d dark, like a beetle. It seemed to her to be moving along the line. But perhaps that was her imagination.

  She continued her careful climb downward.

  “…But then the visitors came in their drifting interstellar moonlets,” Nemoto had said. “And they cared nothing for Venus or its life-forms. They just wanted to steal the moon, to propagate their rocky spore. So they stopped Venus spinning.”

  At the base of the cliffs she paused for a few minutes, letting her heartbeat subside to something like normal, sipping water.

  The black line was a cable. It was maybe two meters thick, featureless and black, and it was held a meter from the ground by crude, sturdy pylons of rock.

  “How do you despin a planet?” Nemoto whispered. “We can think of a number of ways. You could bombard it with asteroids, for instance. But I think Venus was turned into a giant Dyson engine. Carole, I have observed cables like this all over the planet, wrapped east to west. They are fragmentary, broken — after all they are eight hundred million years old — but they still exist in stretches hundreds of kilometers long. Once, I would wager, the surface of Venus was wrapped in a cage of cables that followed the lines of latitude, like geographical markings on a schoolroom globe…”

  She pressed her lab box against the cable. She even ran her hand along it, cautiously, but could feel nothing through the layers of her suit.

  She began to walk alongside the cable. Some of the pylons were missing, others badly eroded. It was remarkable any of this stuff had lasted so long, she thought; it must be strongly resistant to Venus’s corrosive air.

  “Electric currents would be passed through the cables,” Nemoto whispered. “The circulating currents would generate an intense magnetic field. This field would be used to couple the planet to its moon — perhaps the moon was dragged within its Roche limit, deliberately broken apart by tides.