At present — before the flash — Sol was a red giant around two astronomical units across. After the superwind the envelope would be blown into a globe twenty thousand times that size, a billowing, cooling cloud three hundred light days across.
The furthest planet from the heart of old Sol was only forty astronomical units out — six light-hours. So the swelling envelope would, at last, smother all of Sol’s children.
Then, when the superwind was done, the dwarf remnant would emit a new wind of its own: a fizz of hot, fast particles which would blow at the expanding globe, pushing out the inner layers. The globe would become a planetary nebula — a huge, cooling, hollow shell of gas, fluorescing in the light of the dying dwarf at its heart.
Mark said, “At last, of course, the fusing helium in the core will be exhausted. Then the core will shrink once more, until the temperature of the regions around the core becomes high enough for helium fusion to start — in a shell outside the core, but within the hydrogen-burning shell. And the helium fusion will deposit carbon ash onto the core, growing in mass and heating it up — until the fusion of carbon begins…
“The cycle repeats, Uvarov. There will be carbon flashes — and, later, flashes of oxygen and silicon… At last, the giant might have a core of almost pure iron, with an onion-shell structure of fusing silicon, oxygen, carbon, helium and hydrogen around it. But iron is a dead end; it can only fuse by absorbing energy, not liberating it.”
“And all this will happen to the Sun?”
Mark hesitated. “Our standard models say that the reactions go all the way to iron only in stars a lot more massive than the Sun — say, twelve Solar masses or more.” He sighed, theatrically. “Will we get onion-shell fusion in the heart of the Sun? I don’t know, Uvarov. We may as well throw out our theoretical models, I guess. If the photino birds are as widespread as they seem to be, there may not be a single star in the Universe which has followed through a ‘standard’ lifecycle.”
“Superwind,” Uvarov breathed. “How soon is Sol’s helium flash?”
“Lieserl’s observations are sketchy on this. But, Uvarov, the conditions are right. The flash may even have happened by now. The superwind could already be working its way out…”
“How soon, damn you?”
“We have a few centuries. No more.”
Uvarov swept his blind face around the saloon. He pictured the ruined Jovian system beyond these walls, the bloated star dominating the sky outside.
“Then we can’t stay here,” he said.
21
By the time she’d climbed to the top of the giant kapok tree her hand-grips were slick with sweat, and her lungs were pumping rapidly. Spinner-of-Rope took off her spectacles and wiped the lenses on a corner of her loincloth. Zero-gee or not, it still took an effort to haul her bulk around this forest… an effort that seemed to be increasing with age, despite all the AS treatment in the world.
She was at the crown of the kapok. The great tree was a dense, tangled mass of branches beneath her. Seeds drifted everywhere, filling the rippling canopy with points of light — like roaming stars, she thought. Somewhere a group of howler monkeys shrieked out their presence. Their eerie ululations, rising and falling, reminded her of the klaxon which had once called the Undermen to their dreary work…
She put that thought out of her mind with determination. She pulled some dried meat from her belt and chewed on it, relishing the familiar, salty taste. She felt tired, damn it; she’d come here, alone, because she wanted — just for a few hours — to put all of the strangeness below the forest Deck, and beyond the skydome, out of her mind, to immerse herself once more in the simple world in which she’d grown up.
In the distance a bird flapped, shrieking, its colors gaudy against the bland afternoon blue of the skydome.
The bird was flying upside down.
“Spinner-of-Rope.”
The voice was close to her ear. Still chewing her meat, Spinner turned, slowly.
Louise Ye Armonk hovered a few feet away, standing on the squat, neat platform of a zero-gee scooter. Louise grinned. “Did I make you jump? I’m sorry for cheating with this scooter; I’m not sure I would have managed the climb.”
Spinner-of-Rope glared at her. “Louise. Never — never — sneak up on someone at the top of a tree.”
Louise didn’t look too concerned. “Why not? Because you might lose your grip, and drift off the branch a couple of feet? What a disaster.”
Spinner tried to maintain her anger, but she started to feel foolish. “Come on, Louise. I’m trying to make a point.”
Louise, skillfully, brought her scooter in closer to Spinner; without much grace she clambered off the scooter and onto the branch beside Spinner. “Actually,” she said gently, “so am I.” She breathed deeply of the moist forest air, and looked around the sky. “I saw you watching that bird.”
Spinner pushed her spectacles up the bridge of her nose. “So what?”
Louise picked at the tree bark. “Well, the bird seems to be doing its best to get by, in zero-gee.”
“Maybe. Not everyone here is doing so well,” Spinner said heavily. The loss of gravity was, slowly but surely, devastating the forest biota. “The higher birds and animals seem to be adapting okay… The monkeys quickly learned to adjust the way they climb and jump. But otherwise, things are falling apart, in a hundred tiny ways.” She thought of spiders which could no longer spin webs, of tree-dwelling frogs which found their tiny leaf-bound ponds floating away into the air. “We’re doing our best to keep things working — to save whatever we can,” she said. “But, damn it, even the rain doesn’t fall right any more.”
Louise reached out and took her hand; the old engineer’s skin was cold, leathery. “Spinner, we have to reestablish all of this. Permanently.” Louise lifted her face; the diffuse light of the dome softened the etched-in age lines. “I designed this forest Deck, remember. And this is the only fragment of Earth that’s survived, anywhere in the Universe — as far as we know.”
Spinner-of-Rope pulled her hand away. “I know what your little parable about the bird was about, Louise. I should adapt, just like the plucky little bird. Right? You want me to come back to the nightfighter.”
Louise nodded, studying her.
“Well, it was a dumb parable. The bird is the exception, not the rule. And — ”
“Spinner, I know you needed a break. But you’ve been climbing around these trees for a long time, now. I need you to come back — we all do. I know it’s difficult for you, but you’re the only person I have who can do the job.”
Spinner watched her face, skeptically. “But we’re not talking about mere discontinuity-drive jaunts around the Solar System now. Are we, Louise?”
“No.” Louise wouldn’t meet her eyes.
Spinner felt a hollowness in her chest — as if it had expanded, leaving her heart fluttering like a bird in some huge cavity. Hyperdrive…
“Spinner, we need the hyperdrive. You understand that, don’t you? The Sun is dying. Perhaps we could attempt to establish some sort of colony here, in the Solar System. But we need to find out what’s happening beyond the System. Are there any people left, anywhere? Maybe we can join them — find a better place than the Solar System has become.