Using the figures on the present situation, Massy reluctantly arrived at the fact that here, on this already frozen world, the temperature would drop until CO2 froze out of the atmosphere. When that happened, the temperature would plummet until there was no really significant difference between it and that of empty space. It is carbon dioxide which is responsible for the greenhouse effect, by which a planet is in thermal equilibrium only at a temperature above its surroundings—as a greenhouse in sunlight is warmer than the outside air.
The greenhouse effect would vanish soon on the colony world. When it vanished on the mother planet, Massy found himself thinking, if Riki won't leave when the Survey ship comes, I'll resign from the Service. I'll have to if I'm to stay. And I won't go unless she does.
III
"If you want to come, it's all right," said Massy ungraciously.
He waited while Riki slipped into the bulky cold-garments that were needed out-of-doors in the daytime, and were doubly necessary at night. There were heavy boots with inches-thick insulating soles, made in one piece with the many-layered trousers. There was the air-puffed, insulated over-tunic with its hood and mittens which were a part of the sleeves.
"Nobody goes outside at night," she said when they stood together in the cold-lock.
"I do," he told her. "I want to find out something." The outer door opened and he stepped out. He held his arm for her, because the steps and walkway were no longer heated. Now they were covered with a filmy layer of something which, was not frost, but a faint, faint bloom of powder. It was the equivalent of dust, but it was microscopic snow-crystals frozen out of the air by the unbearable chill of night.
There was no moon, of course, yet the ice-clad mountains glowed faintly. The drone-hulls arranged in such an orderly fashion were dark against the frosted ground. There was silence; stillness; the feeling of ancient quietude. No wind stirred anywhere. Nothing moved. Nothing lived. The soundlessness was enough to crack the eardrums.
Massy threw back his head and gazed at the sky for a very long time. Nothing. He looked down at Riki.
"Look at the sky," he commanded.
She raised her eyes. She had been watching him. But as she gazed upward she almost cried out. The sky was filled with stars in innumerable variety. But the brighter ones were as stars had never been seen before. Just as the sun in daylight had been accompanied by its sundogs—pale phantoms of itself ranged about it—so the brighter distant suns now shone from the center of rings of their own images. They no longer had the look of random placing. Those which were most distinct were patterns in themselves, and one's eyes strove instinctively to grasp the greater pattern in which such seeming artifacts must belong.
"Oh…beautiful!" cried Riki softly, yet almost afraid.
"Look!" he insisted. "Keep looking!"
She continued to gaze, moving her eyes about hopefully. It was such a sight as no one could have imagined. Every tint and every color; every possible degree of brightness appeared. And there were groups of stars of the same brilliance which almost made triangles, but not quite. There were rose-tinted stars which almost formed an arc, but did not. And there were arrays which were almost lines and nearly formed squares and polygons, but never actually achieved them.
"It's…beautiful!" said Riki breathlessly. "But what must I look for?"
"Look for what isn't there," he ordered.
She looked, and the stars were unwinking, but that was not extraordinary. They filled all the firmament, without the least space in which some tiny sparkle of light was not to be found. But that was not remarkable, either. Then there was a vague flickering grayish glow somewhere indefinite. It vanished. Then she realized.
"There's no aurora!" she exclaimed.
"That's it," said Massy. "There've always been auroras here. But no longer. We may be responsible. I wish I thought it wise to turn everything back to reserve power for a while. We could find out. But we can't afford it. There was just the faintest possible gray flickering just now. But there ought to be armies of light marching across the sky. The aurora here—it was never missing! But it's gone now."
"I…looked at it when we first landed," admitted Riki. "It was unbelievable! But it was terribly cold, out of shelter. And it happened every night, so I said to myself I'd look tomorrow, and then tomorrow again. So it got so I never looked at all."
Massy kept his eyes where the faint gray flickering had been. And once one realized, it was astonishing that the former nightly play of ghostly colors should be absent.
"The aurora," he said dourly, "happens in the very upper limits of the air…fifty…seventy, ninety miles up, when God-knows-what emitted particles from the sun come streaking in, drawn by the planet's magnetic field. The aurora's a phenomenon of ions. We tap the inonosphere a long way down from where it plays, but I'm wondering if we stopped it."
"We?" said Riki, shocked. "We—humans?"
"We tap the ions of their charges," he said somberly, "that the sunlight made by day. We're pulling in all the power we can. I wonder if we've drained the aurora of its energy, too."
Riki was silent. Massy gazed, still searching. But he shook his head.
"It could be," he said in a carefully detached voice. "We didn't draw much power by comparison with the amount that came. But the ionization is an ultraviolet effect. Atmospheric gases don't ionize too easily. After all, if the solar constant dropped a very little, it might mean a terrific drop in the ultraviolet part of the spectrum—and that's what makes ions of oxygen and nitrogen and hydrogen and such. The ion-drop could easily be fifty times as great as the drop in the solar constant. And we're drawing power from the little that's left."
Riki stood very still. The cold was horrible. Had there been a wind, it could not have been endured for an instant. But the air was motionless. Yet its coldness was so great that the inside of one's nostrils ached, and the inside of one's chest was aware of chill. Even through the cold-garments there was the feeling as of ice without.
"I'm beginning," said Massy, "to suspect that I'm a fool. Or maybe I'm an optimist. It might be the same thing. I could have guessed that the power we could draw would drop faster than our need for power increased. If we've drained the aurora of its light, we're scraping the bottom of the barrel. And it's a shallower barrel than one would suspect."
There was stillness again. Riki stood mousy-quiet. When she realizes what this means, thought Massy grimly, she won't admire me so much. Her brother's built me up. But I've been a fool, figuring out excuses to hope. She'll see it.
"I think," said Riki quietly, "that you're telling me that after all we can't store up heat, to live on, down in the mine."
"We can't," agreed Massy grimly. "Not much, nor long. Not enough to matter."
"So we won't live as long as Ken expects?"
"Not nearly as long," said Massy evenly. "He's hoping we can find out things to be useful back on Lani II. But we'll lose the power we can get from our grid long before even their new grids are useless. We'll have to start using our reserve power a lot sooner. It'll be gone—and us with it—before they're really in straits for living-heat."
Riki's teeth began to chatter.
"This sounds like I'm scared," she said angrily, "but I'm not! I'm just freezing! If you want to know, I'd a lot rather have it the way you say! I won't have to grieve over anybody, and they'll be too busy to grieve, for me! Let's go inside while it's still warm!"
He helped her back into the cold-lock, and the outer door closed. She was shivering uncontrollably when the warmth came pouring in.