Stephen Baxter - Space

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.