Critical Difference

IV

During the last night of preparation, Massy sat by a thermometer registering the outside temperature. He hovered over it as one might over a sick child. He watched it and sweated, though the inside temperature of the drone-hull was lowered to save power. There was nothing he could actually do. At midnight the thermometer said it was seventy degrees below zero Fahrenheit. At halfway to dawn it was eighty degrees below zero Fahrenheit. The hour before dawn it was eighty-five degrees below zero. Then he sweated profusely. The meaning of the slowed descent was that carbon dioxide was being frozen out of the upper layers of the atmosphere. The frozen particles were drifting slowly downward, and as they reached lower and faintly warmer levels they returned to the state of gas. But there was a level, above the CO2, where the temperature was plummeting.

The height to which carbon dioxide existed was dropping—slowly, but inexorably. And above the carbon dioxide level there was no bottom limit to the temperature. The greenhouse effect was due to CO2. Where it wasn't, the cold of space moved down. If at ground level the thermometer read ever so slightly lower than one hundred and nine below zero—why, everything was finished. Without the greenhouse effect, the nightside of the planet would lose its remaining heat with a rush. Even the day-side, once cold enough, would lose heat to emptiness as fast as it came from the sun. Minus one hundred and nine point three was the critical reading. If it went down to that, it would plunge to a hundred and fifty—two hundred degrees below zero! And it would never come up again.

There would be rain at nightfall—a rain of oxygen frozen to a liquid and splashing on the ground. Human life would be quite simply impossible, in any shelter and under any conditions. Even spacesuits would not protect against an atmosphere sucking heat from it at that rate. A spacesuit can be heated against the loss of temperature due to radiation in a vacuum. It could not be heated against nitrogen, which would chill it irresistibly by contact.

But, as Massy sweated over it, the thermometer steadied at minus eighty-five degrees. When the dawn came, it rose to seventy. By mid-morning, the temperature in bright sunshine was no lower than sixty-five degrees below zero.

But there was no bounce left in Massy when Herndon came for him.

"Your phone-plate's been flashing," said Herndon, "and you didn't answer. Must have had your back to it. Riki's over in the mine, watching them get things, ready. She was worried that she couldn't call you. Asked me to find out what was the trouble."

Massy said heavily:

"Has she got something to heat the air she breathes?"

"Naturally," said Herndon. He added curiously,"What's the matter?"

"We almost took our licking," Massy told him. "I'm afraid for tonight, and tomorrow night, too. If the CO2 freezes—"

"We'll have, power!" Herndon insisted. "We'll build ice tunnels and ice domes. We'll build a city under ice, if we have to. But we'll have power. We'll be all right!"

"I doubt it very much," said Massy. "I wish you hadn't told Riki of the bargain to get her away from here when the Survey ship comes!"

Herndon grinned.

"Is the little grid ready?" asked Massy.

"Everything's set," said Herndon exuberantly. "It's in the mine-tunnel with radiant heaters playing on it. The bombs are ready. We made enough to last for months, while we were at it. No use taking chances!"

Massy looked at him queerly. Then be said:

"We might as well go out, and try the thing, then."

But he was very tired. He was not elated. Riki can't be gotten away, he thought wearily, and I'm not going to go because it isn't quite fitting to go and leave her. They'll all be rejoicing presently, but nothing's settled. Then he thought with exquisite irony: She thinks I was inspired to genius by her, when I haven't done a thing I wasn't taught or didn't get out of books!

He put on the cold-garments as they were now modifled for the increased frigidity. Nobody could breathe air at minus sixty-five degrees without getting his lungs frost-bitten. So there was now a plastic mask to cover one's face, and the air one breathed outdoors was, heated as it came through a wire-gauze snout. But still it was not wise to stay out of shelter for too long a time.

Massy went out-of-doors. He stepped out of the cold-lock and gazed about him. The sun seemed markedly paler, and now it had lost its sun-dogs again. Ice crystals no longer floated in the almost congealed air. The sky was dark. It was almost purple, and it seemed to Massy that he could detect faint flecks of light in it. They would be stars, shining in the daytime.

There seemed to be no one about at all, only the white coldness of the mountains. But there was a movement at the mine-drift, and something came out of it. Four men appeared, muffled up like Massy himself. They rolled the eighteen-foot grid out of the mine-mouth, moving it on those inflated bags which are so much better than rollers for rough terrain. They looked absurdly like bears with steaming noses, in their masks and clothing. They had some sort of powered pusher with them, and they got the metal cage to the very top of a singularly rounded stone upcrop which rose in the center of the valley.

"We picked that spot," said Herndon's muffled voice through the chill, "because by shifting the grid's position it can be aimed, and be on a solid base. Right?"

"Quite all right," said Massy. "We'll go work it."

He moved heavily across the valley, in which nothing moved except the padded figures of the four technicians. Their wire-gauze breathing-masks seemed to emit smoke. They waved to him in greeting.

I'm popular again, he thought drearily, but it doesn't matter. Getting the Survey ship to ground won't help now, since Riki's forewarned. And this trick won't solve anything permanently on the home planet. It'll just postpone things.

He had a very peculiar ache inside. A Survey officer is naturally lonely. Massy had been lonely before he even entered the Service. He hadn't had a feeling of belonging anywhere, or with anyone, and no planet was really his home. Now he could believe that he belonged with someone. But there was the slight matter of a drop in the solar constant of an unimportant Sol-type sun, and nothing could come of it.

Even when Riki, muffled like the rest, waved to him from the mouth of the tunnel, his spirits did not lift. The thing he wanted was to look forward to years and years of being with Riki. He wanted, in fact, to look forward to forever. And there might not be a tomorrow.

"I had the control board rolled out here," she called breathlessly through her mask. "It's cold, but you can watch!"

It wouldn't be much to watch. If everything went all right, some dial-needles would kick over violently, and their readings would go up and up. But they wouldn't be readings of temperature. Presently the big grid would report increased power from the sky. But tonight the temperature would drop a little farther. Tomorrow night it would drop farther still. When it reached one hundred and nine point three degrees below zero at ground level—why it would keep on falling indefinitely. Then it wouldn't matter how much power could be drawn from the sky. The colony would die.

One of the figures that looked like a bear now went out of the mine-mouth, trudging toward the grid. It carried a muffled, well-wrapped object in its arms. It stooped and crept between the spokes of the grid. It put the object on the stone. Massy traced cables with his eyes. From the grid to the control board. From the board back to the reserve-power storage cells, deep in the mountain.

"The grid's tuned to the bomb," said Riki breathlessly, close beside him. "I checked that myself!"

The bearlike figure out in the valley jerked at the bomb. There was a small rising cloud of grayish vapor. It continued. The figure climbed hastily out of the grid. When the man was clear, Massy threw a switch.

There was a very tiny whining sound, and the wrapped, ridiculously smoking object leaped upward. It seemed to fall toward the sky. There was no more of drama than that. An object the size of a basketball fell upward, swiftly, until it disappeared. That was all.

Massy sat quite stiff, watching the control-board dials. Presently he corrected this, and shifted that. He did not want the bomb to have too high an upward velocity. At a hundred thousand feet it would find very little air to stop the rise of the vapor it was to release.

The field-focus dial reached it's indication of one hundred thousand feet. Massy reversed the lift-switch. He counted and then switched the power off. The small, thin whine ended.

He threw the power-intake switch, which could have been on all the time. The power-yield needle stirred. The minute grid was drawing power like its vaster counterpart. But its field was infinitesimal by comparison. It drew power as a soda straw might draw water from wet sand.

Then the intake-needle kicked. It swung sharply, and wavered, and then began a steady, even, climbing movement across the markings on the dial-face. Riki was not watching that.

"They see something!" she panted. "Look at them!" The four men who had trundled the smaller grid to its place, now stared upward. They flung out their arms. One of them jumped up and down. They leaped. They practically danced.

"Let's go see," said Massy.

He went out of the tunnel with Riki. They gazed upward. And directly overhead, where the sky was darkest blue and where it had seemed that stars shone through the daylight—there was a cloud. It seemed to Massy, very quaintly, that it was no bigger than a man's hand. But it grew. Its edges were yellow—saffron-yellow. It expanded and spread. Presently it began to thin. As it thinned, it began to shine. It was luminous. And the luminosity had a strange, familiar quality.

Somebody came panting down the tunnel, from inside the mountain.

"The grid—" he panted. "The big grid! It's pumping power! Big power! BIG power!"

He went pounding back, to gaze rapturously at the new position of a thin black needle on a large white dial, and to make incoherent noises of rejoicing as it moved very, very slowly toward higher and ever higher readings.

But Massy looked puzzledly at the sky, as if he did not quite believe his eyes. The cloud now expanded very slowly, but still it grew. And it was not regular in shape. The bomb had not shattered quite evenly, and the vapor had poured out more on one side than the other. There was a narrow, arching arm of brightness—"It looks," said Riki breathlessly, "like a comet!"

And then Massy froze in every muscle. He stared at the cloud he had made aloft, and his hands clenched in their mittens, and he swallowed convulsively behind his cold-mask.

"Th-that's it," he said in a very queer voice indeed. "It's…very much like a comet. I'm glad you said that! We can make something even more like a comet. We…we can use all the bombs we've made, right away, to make it. And we've got to hurry so it won't get any colder tonight!"

Which, of course, sounded like insanity. Riki looked apprehensively at him. But Massy had just thought of something. And nobody had taught it to him and he hadn't gotten it out of books. But he'd seen a comet.

The new idea was so promising that he regarded it with anguished unease for fear it would not hold up. It was an idea that really ought to change the facts resulting naturally from a lowered solar constant in a Sol-type star.

Half the colony set to work to make more bombs when the effect of the second bomb showed up. They were not very efficient, at first, because they tended to want to stop work and dance from time to time. But they worked with an impassioned enthusiasm. They made more bomb-casings, and they prepared more sodium and potassium metal and more fuses, and more insulation to wrap around the bombs to protect them from the cold of airless space.

Because these were to go out to airlessness. The miniature grid could lift and hold a bomb steady in its field focus at seven hundred-and fifty thousand feet.But if a bomb was accelerated all the way out to that point, and the field was then snapped off—Why, it wasn't held anywhere. It kept on going with its attained velocity. And it burst when its fuse decided that it should, whereupon immediately a mass of sodium and potassium vapor, mixed with the fumes of high explosive, flung itself madly in all directions, out between the stars. Absolute vacuum tore the compressed gasified metals apart. The separate atoms, white-hot from the explosion, went swirling through sunlit space. The sunlight was dimmed a trifle, to be sure. But individual atoms of the lighter alkaline-earth metals have marked photoelectric properties. In sunshine these gas-molecules ionized, and therefore spread more widely, and did not coalesce into even microscopic droplets.

They formed, in fact, a cloud in space. An ionized cloud, in which no particle was too large to be responsive to the pressure of light. The cloud acted like the gases of a comet's tail. It was a comet's tail, though there was no comet. And it was an extraordinary comet's tail because it is said that you can put a comet's tail in your hat, at normal atmospheric pressure. But this could not have been put in a hat. Even before it turned to gas, it was the size of a basketball. And, in space, it glowed. It glowed with the brightness of the sunshine on it, which was light that would normally have gone away through the interstellar dark. And it filled one corner of the sky. Within one hour it was a comet's tail ten thousand miles long, which visibly brightened the daytime heavens. And it was only the first of such reflecting clouds.

The next bomb set for space exploded in a different quarter, because Massy'd had the miniature grid wrestled around the upcrop to point in a new and somewhat more carefully chosen line. The third bomb spattered brilliance in a different section still. And the brilliance lasted.

Massy flung his first bombs recklessly, because there could be more. But he was desperately anxious to hang as many comet tails as possible around the colony planet before nightfall. He didn't want it to get any colder.

And it didn't. In fact, there wasn't exactly any real nightfall on Lani III that night.

The planet turned on its axis, to be sure. But around it, quite close by, there hung gigantic streamers of shining gas. At their beginning, those streamers bore a certain resemblance to the furry wild-animal tails that little boys like to have hanging down from hunting-caps. Only they shone. And as they developed they merged, so that, there was an enormous shining curtain about Lani III. There were draperies of metal-mist to capture sunlight that should have been wasted, and to diffuse very much of it to Lani III. At midnight there was only one spot in all the night-sky where there was really darkness. That was directly overhead—directly outward from the planet from the sun. Gigantic shining streamers formed a wall, a tube, of comet-tail material, yet many times more dense and therefore brighter, which shielded the colony world against the dark and cold, and threw upon it a brilliant, warming brightness.

Riki maintained stoutly that she could feel the warmth from the sky, but that was improbable. But certainly heat did come from somewhere. The thermometer did not fall at all, that night. It rose. It was up to fifty below zero at dawn. During the day they sent out twenty more bombs that second day—it was up to twenty degrees below zero. By the day after, there was highly competent computation from the home planet, and the concrete results of abstruse speculation, and the third day's bombs were placed with optimum spacing for heating purposes.

And by dawn of the fourth day the air was a balmy five degrees below zero, and the day after that there was a small running stream in the valley at midday.

There was talk of stocking the stream with fish on the morning the Survey ship came in. The great landing-grid gave out a deep-toned vibrant, humming note, like the deepest possible note of the biggest organ that could be imagined. A speck appeared very, very high up in a pale-blue sky with trimmings of golden gas-clouds. The Survey ship came down and down and set, tied as a shining silver object in the very center of the gigantic red-painted landing-grid.

Later, her skipper came to find Massy. He was in Herndon's office. The skipper struggled to keep sheer blankness out of his expression.

"What…what the hell?" he demanded querulously of Massy. "This is the damnedest sight In the whole galaxy, and they tell me you're responsible! There've been ringed planets before, and there've been comets and who-knows-what! But shining gas pipes aimed at the sun, half a million miles across…What the? There are two of them! Both the occupied planets!"

Herndon explained with a bland succinctness why the curtains hung in space. There was a drop in the solar constant.

The skipper exploded. He wanted facts! Details! Something to report! And dammit, he wanted to know!

Massy was automatically on the defensive when the skipper shot his questions to him. A Senior Colonial Survey officer is not revered by the Survey ship-service officers. Men like Massy can be a nuisance to a hardworking ship's officer. They have to be carried to unlikely places for their work of checking over colonial installations. They have to be put down on hard-to-get-at colonies, and they have to be called for, sometimes, at times and places which are inconvenient. So a man in Massy's position is likely to feel unpopular.

"I'd just finished the survey here," he said defensively, "when a cycle of sunspot cycles matured. All the sunspot periods got in phase, and the solar constant dropped. So I naturally offered what help I could to meet the situation."

The skipper regarded him incredulously.

"But…it couldn't be done!" he said blankly. "They told me how you did it, but…it couldn't be done! Do you realize that these vapor-curtains will make fifty border-line worlds fit for use? Half a pound of sodium vapor a week!" He gestured helplessly. "They tell me the amount of heat reaching the surface here has been upped by fifteen per cent! D'you realize what that means?"

"I haven't been worrying about it," admitted Massy. "There was a local situation and something had to be done. I…er…remembered things, and Riki suggested something I mightn't have thought of, and it's worked out like this." Then he said abruptly: "I'm not leaving. I'll get you to take my resignation back. I...I think I'm going to settle here. It'll be a long time before we get really temperate-climate conditions here, but we can warm up a valley like this for cultivation, and…well…it's going to be a rather satisfying job. It's a brand new planet with a brand-new ecological system to be established—"

The skipper of the Survey ship sat down hard. Then the sliding door of Herndon's office opened and Riki came in. The skipper stood up again. Massy rather awkwardly made the introduction. Riki smiled.

"I'm telling him," said Massy, "that I'm resigning from the Service to settle down here."

Riki nodded. She put her hand in proprietary fashion on Massy's arm. The Survey skipper cleared his throat.

"I'm not going to take it," he said doggedly. "There've got to be detailed reports on how this business works. Dammit, if vapor-clouds in space can be used to keep a planet warm, they can be used to shade a planet, too! If you resign, somebody else will have to come out here to make observations and work out the details of the trick! Nobody could be gotten here in less than a year! You need to stay here to build up a report—and you ought to be available for consultation when this thing's to be done somewhere else! I'll report that I insisted as a Survey emergency—"

Riki said confidently:

"Oh, that's all right! He'll do that! Of course! Won't you?"

Massy nodded dumbly. He thought, I've been lonely all my life. I've never belonged anywhere. But nobody could possibly belong anywhere as thoroughly as I'll belong here when it's warm and green and even the grass on the ground is partly my doing. But Rikki will like for me still to be in the Service. Women like to see their husbands wearing uniforms.

Aloud he said:

"Of course. It…really needs to be done. Of course, you realize that there's nothing really remarkable about it. Everything I've done has been what I was taught, or read in books."

"Hush!" said Riki. "You're wonderful!"