Stephen Baxter: Ark

Huddling for warmth, Earth III orbited so close to its parent star that tides had long since massaged its rotation so that its day equalled its year, and it kept the same face permanently turned toward its sun. One side was in perpetual light, the other in unending darkness, save for the starlight. But even the side of perpetual day was so cold that glaciers draped equatorial mountaintops.

Maybe it was habitable. It was not like Earth. That was the basic truth that was driven home to Helen even as she first examined these images, even as Venus began to describe the new world.

Venus said, “Earth III is the innermost planet in its system, but there are other planets further out. More Earths and super-Earths. Not as easy to colonize as Earth III, but they’re there for our descendants-new homelands just waiting in the sky for them, off in the future.

“We looked for planets in the habitable zones of stars, that is the orbital radius where liquid water is possible on the surface, and that’s just what we found here. You can see the oceans. But this M-sun is a lot dimmer than Sol, so Earth III has to be closer in to its parent, only about ten million kilometers out-much less than the orbit of Mercury. The year is different, of course. Earth III’s year is just fifteen of our days long. The stars will shift quickly in the sky. But there is no ‘day,’ and there are no seasons. From the ground you will never see the sun move from the same position in the sky. And it’s cool. Even at the subsolar point you’ll only get about sixty percent of the radiant energy as you’d receive from the sun, on Earth. If you’re on the night side you never see the sun at all.” She pointed. “There’s an ice cap at the point of deepest shadow, as you can see. It gets pretty cold back there.

“You might wonder why the air doesn’t all freeze out on the dark side. It doesn’t work like that; the atmosphere is thick, full of greenhouse gases injected by volcanoes, a blanket that transports heat around the world. Also you have the planet’s own inner heat, which is greater than Earth’s. The climate is stable. It’s just different.

“And Earth III is larger than the Earth-that’s the most basic fact about it. It’s an exoplanet of the kind the planet-hunters called a super-Earth. It has around twice Earth’s mass, and maybe twenty-five percent higher gravity. That will feel hard, but you’ll soon muscle up, and your children will grow up stockier than you are and won’t even notice.

“More planetary mass is good, and it’s one reason we selected this world. More mass means more inner heat, a thinner crust, plate tectonics, a spinning iron core. That core produces a healthy magnetosphere, so there is plenty of shelter from radiation, both from the M-sun’s flares and from cosmic radiation. And you can see the evidence of the plate tectonics for yourself. Lots of mountain-building, and active volcanoes.” She pointed to the horizon. “See the layer of dust and ash up there? Volcano smog. Plate tectonics keep a world young. The good news is that this world, being more massive, will keep its inner heat longer than Earth. Earth III will stay young, long after Earth itself has seized up and turned into a bigger copy of Mars.

“And there is life here. We knew that from the spectroscopic studies we did of the atmosphere from light-years away. There is photosynthesis going on in the oceans. On the continents, you can see there are bands of different vegetation types working out from the subsolar point, adapted to the lower light levels. We think we’ve seen living things even in the twilight band, around the rim of the daylit face, at the terminator. Like trees maybe, straining up so their leaves can catch the last scraps of light. That’s something for you to find out, some day.”

She looked around, an earnest, exuberant woman, testing to make sure they understood the nature of this gift she was presenting to them. “So you have a sun that will last a hell of a lot longer than Sol, and an Earth that will stay young too, and more worlds to explore. We couldn’t have found a better refuge for your children, for mankind, stretching off into the distant future.

“This is the Ark. After a voyage of forty years, here is your Ararat.” She stepped back.

But she was met by silence, and blank looks. Perhaps the world she had given them was simply too strange.

Then Holle came forward, her face tough, determined, her eyes sunken. Everybody was silent and stock still, save for a few wriggling children. Even little Hundred seemed to be paying attention. Holle’s grim expression was racking up the tension. Helen suddenly realized she had no idea what Holle was about to say.

“Thanks, Venus,” Holle said. “So much for the good news. Now we have to talk about landfall. We have a problem.”

“Most of you don’t even remember how the Ark was when it was launched. There were two hulls, called Seba and Halivah. And we had four shuttles, each capable of taking around twenty-five people down to the target planet. We launched from Earth with under eighty crew, a bit less than the design limit. We figured that we would have plenty of capacity in the shuttles, even allowing for a few births along the way.

“But it didn’t turn out that way. You all know what happened. We got to Earth II thirty years ago, and split up. Seba went back to Earth, taking one shuttle with it. We used another shuttle to land the colonists who opted to stay at Earth II. That left two more, for us to take to Earth III-but we lost another on the way, during the Blowout.” A few of the older people glanced at Wilson, who hung defiantly in the upper section of the hull.

“So we arrived here,” Holle said, “with just one shuttle. The shuttle is basically a twenty-five-seat glider; it’s only equipped to make one trip, one descent to the surface. The design was like that to save weight. It can’t take off again and return to the hull…”

Helen’s anxiety tightened. She had known there was a problem with shuttle capacity since the aftermath of the Blowout. But back then landfall had been years away. Holle, tough, autocratic, always kept a lot of her decisions and deliberations secret. Helen had trusted Holle to come up with a solution in time. Now, it seemed, that trust might have been misplaced.

“I’m sorry,” Holle said bluntly. “We tried everything we could think of to improvise some other way of getting down to the planet’s surface. The trouble is that heavy gravity, the thick atmosphere. There will be a ferocious frictional load as any entry craft dumps its orbital energy. The shuttle is designed to cope with that; it has a properly engineered heat shield. Nothing we could lash up comes close to that capability.” She paused, and there was silence, save for a baby’s sleepy murmur. “You need to understand clearly. We got you here. We came all this way, and some of you will walk on Earth III. But I can’t take you all down to the surface.”

“And what of the rest?” somebody shouted.

“I’ll stay with you,” Holle said immediately.

“You’ll stay with us to die? Is that the deal?”

“Nobody’s going to die.” Venus pulled her way forward so she was beside Holle. “We just won’t leave the ship, is all. We will go on. The ship is still functioning, it has water, air, power. And we can still use the warp generator-”

“Zane’s dead.”

“We can trigger the warp bubble without Zane.” Holle forced a smile. “We can go wherever we want.”

Max Baker drifted forward. “Some are going to make landfall, some will stay here. Twenty-five of us will go down, I guess. Who, Holle? How will we decide? Is there going to be some kind of ballot?”

“No,” Holle said firmly. “We don’t have that luxury. We have to get this right. I’ll decide-I have decided.”