Stephen Baxter - Ark

“This much we were able to guess from observations from Earth and Jupiter,” she said. “But all we could see from the solar system was a blurry dot with some evidence of mass, orbit, atmospheric composition. That’s all. On that basis it looked promising. But as it’s turned out, Earth II is not that close a sister to Earth I.

“This is a much less active world than Earth, geologically. You can see that from the eroded chains of mountains, the flat landscapes. The penetrators’ seismometers have detected few earthquakes. And we see no significant evidence of continental drift, no active plate-forming mid-ocean ridges, no subduction zones at plate boundaries-no colliding plates to trigger volcanism and to throw up mountain chains, as on Earth.

“Tectonic shift has seized up, here. It’s not absent, but is clearly operating at a much reduced rate than on Earth. And the result is the geology we see. The Frisbee is not unlike Australia, ancient and stable, so old its mountains are worn down, the rocks shattered to dust and rusted red. The big volcano at the heart of the Frisbee is a shield volcano, like Hawaii on Earth, and just like Olympus Mons on Mars-we named it well. It’s been created by a magma plume, an upwelling of hot material from the planet’s mantle, like a fountain. Olympus has been stuck over that plume for a long time-hundreds of millions of years, maybe. Over similar periods on Earth, the continents slide all the way from equator to pole.

“Is that important? We think so, for the sake of the long-term habit-ability of the planet. On Earth, plate tectonics play a key part in the vast geological and biological cycling that maintains Gaia. This world, with tectonic processes much reduced, can’t sustain such a significant cargo of life.

“Why has Earth II turned out to be so much less active than Earth? First, Earth II is that much smaller than Earth. Like Mars, it must have shed a greater proportion of its interior heat of formation, and a greater proportion of its inventory of radioactive materials will have decayed away. So the big internal heat engine that drives plate tectonics has run down. And second, we believe Earth II is actually an older world than Earth, by a billion years or more; whatever triggered planet-forming in this system happened much earlier than back home.”

Wilson put in, “So a billion years ago this world might have looked that much more like Earth.”

“Yes. With a much richer biosphere. I think we can expect to find traces of past complexity, lost as the planet has run down. That may be why we see no traces of extant intelligence.”

Kelly seized on that word. “ ‘Extant’? Does that imply you found traces of nonextant cultures?”

Holle felt unreasonably excited.

For answer, Venus tapped a handheld.

The turning world winked out of existence, to be replaced by an image of one of the larger islands of the Scatter, as if seen from a low-flying aircraft. Once it may have been mountainous; now its mountains were worn to stubs. “We call this Little Jamaica.” Venus pointed to features on a plain close to the sea. “Can you see?” There were faint circles, hints of straight-line features. “We don’t know what this is. You need to remember that this island is covered by the pack ice every local winter; any traces of surface structures, of buildings and cities, would long ago have been destroyed. It could be the trace of a quarry, we think. That might survive as long as a billion years. Maybe it’s something else, like a city. There are other indicators of intelligence. We’ve found no evidence of deep-buried carbon deposits. If there was any oil or coal on this world, or the local equivalent, it’s long gone. No evidence of particularly rich seams of mineral ores near the surface. A paucity of asteroids in this system, too.”

Wilson folded his arms. “I don’t get it. These are indicators of what?”

“That somebody used up the easily available resources-the oil, the easily mined ores, even off-world resources in the asteroids. And then they died out, or went away. We might find direct evidence one way or the other when we start doing some real archaeology down on the surface.” She shrugged. “There’s a lot of sand to sift.”

“My God,” Holle whispered.

“I know,” Kelly said. “It’s not good for us. But isn’t it wonderful?” And, just for a moment, it was as if they were Candidates again, marveling together over some wondrous bit of scholarship. But they weren’t here for scholarship today.

Somebody called, “And what about the obliquity? I thought that was the big problem.”

Venus allowed herself a rueful smile. “I was saving the best until last.”

She brought up a fresh display. This showed Earth II and its sun, 82 Eridani. The diagram wasn’t to scale, planet and star looking like two light-bulbs, and the planet’s orbit was a glowing yellow circle around the sun. The planet’s rotation axis showed as a glowing splinter pushed through its bulk, a splinter that pointed almost directly at the sun.

Venus said, “As the planet goes around the sun, the axis keeps pointing the same way-just as for Earth. You can see the consequences.” She tapped a key and the planet zipped around its star, keeping its axis pointing in the same direction in space. Earth II’s year was about the same as Earth’s, so after six months the north pole would be plunged into shadow, while its south pole was in the light. “Earth’s obliquity, the tilt of its axis, is about twenty-three degrees, compared to Earth II’s ninety. Life on Earth evolved to cope with moderate seasonality. Here you have the most severe seasonality you can imagine.

“Every part of the planet except an equatorial strip will suffer months of perpetual darkness, months of perpetual light. Away from the equator you’ll suffer extreme heat, aridity, followed by months of Arctic cold-we estimate the surface temperature will drop to a hundred degrees below across much of the space-facing hemisphere, and there’ll be one hell of a blanket of snow and ice. Even the equator would be a challenge to inhabit, for even at the height of summer in either hemisphere the sun would be low, the heat budget minimal, the climate wintry.”

Venus restored the image of the planet, the tilted-over world with its friendly looking continents. Now she made the image accelerate through a simulation of its seasonal cycles. Ice crusted the continents, only to clear and leave them desiccated, brick red. “We can’t survive this,” she said. “Oh, maybe we could adapt to one extreme or another. But not to these swings, year on year, from baking aridity to an Antarctic chill. Our plants, our animals, couldn’t cope with it either. The only possible habitation would be on the equator, but there’s very little equatorial land, a few islands and a slice of the Belt… We lucked out. We couldn’t see the rotation axis from Earth. We couldn’t have predicted these features.”

She fell silent. Her audience, in silence save for the wriggles of children, gloomily watched as her toy planet suffered its cycling seasons.

Theo Morell surprised Holle by calling down, “You say this wasn’t visible from the Earth. OK. But you must have been aware of some of these problems, particularly the axis thing, from further out. You’ve spent the last ten years looking out of that cupola of yours.”

“Yes, I-”

“When did you know Earth II was going to be a bust?”

Venus glanced at Wilson, who shrugged and looked away. “Around two years ago. The data started hardening then-we’d had some suspicions. Two years ago I was sure enough to take it to Wilson, for instance.”

Mentioning Wilson was a way to bring herself into his protection, Holle realized. But the mood in the chamber was switching, through shock and disappointment to a kind of anger. Theo shouted, “And you kept them a secret, these ‘suspicions’ of yours?”