by Hal Clement
“A good thought,” agreed the diamond. “It would be a pity to have to turn back just as data are starting to cut down the possibilities to a really manageable set. I predict that the valley will at least double its width in the next ten kilometers.”
“I’ll go that far without any food, if you’re that near a solution. But let’s check this chimney first.”
The feature in question was a fairly typical crack, ranging from one to two meters wide, in the cliff wall. It appeared to start at the point where the rock itself became nearly vertical; probably it went lower, but was hidden by the rubble which formed the rounded base of the wall. A climb of nearly a hundred meters was necessary to make the study they wanted.
This took only a few minutes. The numerous projecting rocks which served as steps were worn very smooth, presumably by blowing dust or sand, but were so firmly buried in loess as to be completely safe. With frost crystals crunching under his feet, Faivonen took a zigzag path to the bare rock; from that point he was able to follow a shelf where coarser and evidently softer sandstone had been eroded away, straight to the chimney itself.
The examination was brief; the crack was almost solidly choked with frost.
“Not radiation cooling,” Faivonen remarked categorically.
“I agree,” replied Beedee.
“You know what did it.” The man’s words were a declaration, not a question.
“I believe I have a unique solution for this aspect of the problem.”
“And I should be able to find the same one.”
“You should. All pertinent data are available to you.”
Faivonen thought deeply as he picked his way back down to the valley floor and headed up the valley once more, but failed to come up with any solutions, unique or even believable. Increasing hunger finally diverted his attention from the problem.
“Did you see any animals while we were up there?” he asked the diamond.
“None, nothing moving in any part of the valley I could examine. I did not mention it because you said you would go at least ten kilometers farther anyway.”
“Thanks. What do you think the chances are of finding them in this frozen area?”
“I have not enough information for a reliable estimate.”
“Could these animals survive the conditions which you believe caused the frost?”
“Not by any special physiological machinery we have found in them. Such techniques as hibernation would involve biochemical factors not obvious to gross examination, of course.”
“Could I survive those conditions?”
“No.”
“But you can warn me in time to escape them.”
“I believe so. There are variables—”
“I know there are variables, blast you. Are you walking me into something I’d have to catch a couple of dozen balloons to lift me out of?”
“That number would be insufficient, and you might have trouble securing their cooperation—”
“Cut it out! You know perfectly well when I’m being figurative!”
“I am never certain about it. Your wife was much easier to judge in such—”
“Shut up!”
Faivonen strode on in silence for two or three kilometers. After the first five minutes or so, he realized that Beedee had done a competent job of changing the subject on him, and he still didn’t know how much risk he was taking; but he didn’t see any use going back to the matter, and he felt reasonably sure that the diamond would not take really serious chances with its own transportation. Gradually, he cooled down to the point where he could pay attention to his business once more.
The frost was slowly vanishing from the near side of the valley, under the rather unimpressive glow of the twin suns—a glow currently reduced by the fact that one of them was eclipsing the other. Argo, the real heat source for its satellite, was too low to help even if a slight turn in the canyon, some scores of kilometers back, had not blocked its radiation from the valley floor anyway.
When he finally spoke to Beedee again, it was not about personal risks.
“How much useful information do you really think we can get by going, say, a hundred kilometers farther, if that is possible?” he asked. “We have a good idea of the local geology—at least, as good as we can get without drilling—and an even better one of the biology and ecology. Of course, any additional information is always good—I go along with you on that, even if I don’t have your burn for detailed knowledge—but aren’t we maybe getting to the point where what we’ve already learned should be brought back and reported?”
“In those fields, perhaps yes,” was the answer. “However, the meteorology still baffles me seriously. We really must learn more about the atmospheric tides which I believe are controlling so much of what goes on in this valley. If I can work them out in detail, I believe we can infer more about the physiography of the cold side of Medea than could be learned by many hundreds of man-days of surface mapping even if men could venture there. I consider it vital that we go on for a while yet.”
“Regardless of risk.” It was not a question.
“Not entirely, of course. I will do my best to keep you well enough informed to get us back safely, though like you I accept the fact that research entails risk. After all, while I was quite certain that you would come looking for your wife and therefore would find me, I am not nearly so sure that anyone would—or could or should, in this part of the world—come looking for you.”
“They’d surely come for you.”
“I doubt it. Sullivan would be the most strongly tempted, but would certainly not leave his ship. I would not be willing to bet my consciousness on the chance of anyone else on the Fahamu coming, even if Sullivan were willing to work such a trip into the ship’s schedule. I am as strongly concerned about your safety as I was about—” The machine’s voice broke off.
Faivonen knew what the missing word would have been, just as well as he knew that the interrupted sentence had not actually been a mistake; it was another deliberate action by the diamond. He decided not to play up, this time.
“All right. We’ll go on for at least twelve hours, unless you warn me back. Keep your senses tuned up for animals, please. The food situation is getting a little tense.”
Beedee acknowledged the request, and another score of kilometers were traversed with little worth noting except the melting of most of the frost and the fulfilling of Beedee’s valley-width prophecy. They finally stopped for rest. There was nothing to eat but cheese, since they had seen no animal life, but he lit a fire anyway; and, with some Trouble, dug a shallow sleeping pit in the not-quite-frozen ground. The wind was starting to strain the performance of coverall and sleeping bag; balloons were now sweeping by them from behind at running speed, at times bouncing against bushes.
“Do you suppose it’s the low temperature that brings them down this far?” the man wondered aloud.
“Not for simple physical reasons. A given mass of hydrogen or other light gas would have the same lift in a given atmosphere at any temperature. The balloons do not seem to have shrunk, and a temperature drop for a given volume, if shared by the surrounding atmosphere, would increase the lift. Of course, if the creatures can alter internal pressure by muscular contraction of their sacks, or do something to raise internal temperature, the set of possible responses is greatly enlarged. A detailed examination of one of them would be interesting and useful.”
“Hasn’t anyone done it already?”
“It has not been reported to me. The creatures seem to have been given a very low research priority after being found inedible.
I would not have approved, myself, of such an evaluation.”
“Naturally not. Well, we’ll fit that in if we can. Stay on your toes; I’m going to sleep for a few hours.” Faivonen slipped the blinders on.
He woke up five or six hours later, unpleasantly chilled. Keeping as low as possible behind the low pile of soil he had excavated—the wind was not strong, but very not
iceable—he placed most of the fuel he had stacked beside his sleeping pit to help break the wind on the remains of the long-dead fire, and lighted it. When it blazed up he rose to sitting position to let its radiation reach more of his body; and as he did so, Beedee’s voice—no, it was Riita’s voice!—suddenly sounded.
“Elisha! Get to the cliff and start climbing at once! Waste no time!”
Being human, Faivonen did waste a little time. He reached for the equipment he had discarded on lying down, which cost him a second or two; as he ran toward the nearby valley wall, still fastening gear about his person, he looked up the valley and almost lost several more.
Some kilometers away—he could not judge more precisely—an almost featureless white cloud was bearing down on them. It spread low across the valley from wall to wall. Its upper surface was sharply defined, but he could see for some distance into the lower portion. Its height was somewhat under half that of the canyon walls.
From ground level he could not judge its speed, but had a strong impression that it was approaching rapidly. Beedee’s evident opinion that it was dangerous could probably be trusted, anyway, and Faivonen ran his hardest.
It was only a short distance to the point where the wind-rounded rubble began to slow him down. It also, very shortly, brought him to a height where he could judge the distance and speed of the menace for himself. Neither item of information was encouraging. He saw little chance of getting above it before it reached him, but he had no idea of giving up and spending the time before it arrived in thinking up reasons why it was probably harmless.
Details became clearer as the thing drew closer and the man climbed higher. He remembered seeing something like it in a museum on Earth, in a wave demonstration tank where two immiscible liquids sloshed back and forth. He remembered the crawl of the denser fluid along the tank bottom as the container slowly tilted, and how the lighter material was forced up and out of the way.
He remembered pictures of a similar situation which had seen later, when he was studying meteorology—the cross section of a cold front . . .
And suddenly he realized what it must be, and redoubled his climbing effort. Cursing his own shortsightedness could come later, when the breath might be available.
“Beedee!” he panted, “I suppose this was your solution. I take it you didn’t call the time quite correctly.”
“It is. I couldn’t. The region beyond our sight must broaden into a bowl in its general arrangements, but I have no data on the bowl’s size. Hence, the sloshing of the dense gas under tidal influence has a natural period which I was unable to calculate, though the observed changes in the valley wind eliminated many possibilities. There must be funnelling effects at various places along the valley, and these were quite impossible to calculate. There must be some critical time, as spring advances, when the contents of the bowl not only pour for some distance down the valley but actually start a siphoning effect. I trust this is not the time. When that happens, there will be a high, uninterrupted wind of carbon dioxide all the way to the sea—no doubt the cause of the peculiar erosional features we have observed from the beginning.”
“I guessed about the CO2 when I saw how sharp the upper surface of the gas river was. It’s the coldest cold front anyone ever saw—”
“Don’t waste your breath in speech. You seem to have analyzed the situation correctly, but you will have to get above that gas surface or drown. You probably see now as well as I do how the thing formed in the first place, but this is not the time to discuss it. Climb!”
“All right. Just don’t use Riita’s voice again, no matter how urgently you want my attention.”
Beedee made no answer to this, and Faivonen continued up the steepening slope, still snatching occasional glances at the approaching river of frigid gas. Its boundary was clearly marked by the water it froze out of the air it met. Tiny snowflakes settled through it, giving the mass a foggy appearance from a distance. The upper surface looked sharp mostly because the man’s line of sight was nearly parallel to it.
It was also marked, he saw as it drew nearer, by larger specks which he finally realized were balloons. Their buoyancy, as he and Beedee had seen, was for some reason low enough to let them reach the ground in ordinary air, but they floated on top of the carbon dioxide to emphasize the outline provided by the snow.
Looking back and down, in the brief instants he dared do so, he could see the creatures being scooped up as the front reached them. They looked as helpless as he was beginning to feel. His arms and legs ached, his breath was scratching at his throat, and his heart was pounding. He was tempted to drop some of his equipment, but it was already at a minimum likely to keep him alive if he got through the present jam.
The front at the valley floor level was within a kilometer of his camp—farther back, thank goodness, at his present height—it had a shallow slope; every meter he climbed was giving him more time—that would be a good calculus exercise—no, waste of time, Beedee must have it figured out already except for a few variables involved in the terrain he was trying to climb over—it was funny what a person’s mind would do when it wasn’t being put to important work.
Now the ground-level leading edge of the front had passed below him. The valley to his right was floored with a foggy whiteness which became sharper and more opaque as the eye followed it toward the horizon. The top of the snowstorm was climbing toward his feet, the site of his camp disappearing through the thickening precipitation. The fire had vanished between two breaths; its only trace was a vague patch of smoke which had been lifted like the balloons and was spreading into invisibility as it rose toward him.
“Elisha! To your right—ten meters—a chimney. Get into it!”
“Why?” Faivonen slanted in the direction mentioned, even though the reason was not yet clear to him. “It will fill with gas as quickly as the rest of the valley, and there’s no reason to suppose I can climb any faster there.”
“You probably can’t, but I sense turbulence at its edges. The gas is mixing with air there, and should remain breathable longer. Try it. As I read the currents where the front has reached it lower down, there must be good air being forced up from below inside the crack.”
Faivonen didn’t see what he could lose, and where hand-and foot-holds permitted a choice he favored the way toward the opening. He was by now well above the talus and climbing bare but greatly weathered rock. As had been the case farther down the valley, occasional layers of softer sediments had eroded more rapidly to provide shelves and steps; the climbing was not essentially difficult, but hoisting his eighty kilograms of self and equipment even with good footing at the speed which seemed necessary called for a high power consumption.
But climbing inside the chimney would be too slow, though he knew the techniques well enough. Beedee saw this, once they were able to look in, as quickly as the man did.
“Stay as close as you can. There’ll be oxygen for longer. Another fifty or sixty meters will get us out of danger anyway.”
“Don’t talk! Keep quiet and climb! I’m talking so you won’t. Listen all you want, but if you disagree with me keep it to yourself until later. I just remembered another factor; I wish I could evaluate it numerically. The gas lake feeding this river must not only be sloshing under tidal influence, but be expanding thermally as spring advances. It’s getting deeper, and would overflow down this valley, I judge, even without the tides. The diurnal variation in solar heating would have the same frequency as the tide, of course, but probably not the same phase—a really interesting new family of variables—”
Faivonen glanced back and down, which was what Beedee had been hoping to forestall. The snowflakes were very close below.
“Twenty more meters should make us relatively safe. There’s a good ledge there—”
Cold suddenly bit through the coverall. The rock seemed almost hot by contrast, and he was tempted to press against it and stop climbing. The air coming into his nose felt like fire, and he pulled his mask comp
letely over the lower half of his face. The chill may have helped save him; he could feel the urge to breathe faster as the gas reached his blood, but the pain drove him to inhale as slowly as possible. Hyperventilation, especially in Medea’s oxygen-rich atmosphere, could have cost him his physical coordination.
There must be some mixing; he was holding on to consciousness, so there must be enough oxygen—or nearly enough; there was a curtain of darkness twisting about the edges of his field of vision. Beedee was talking again, giving very precise directions where to put his hand, and then his other hand, and then one foot, and then the other . . .
His vision cleared, and his mind slowly followed. The snow was below him again, and he could breathe without pain. He was not, however, out of trouble.
He was on a ledge, presumably the one Beedee had mentioned, and seemed in no immediate danger of falling from it; but there was no obvious way of getting off it by any other method, either. Below, the way he had come, the cliff was climbable but bathed in the frigid gas. Above, the rock was sheer and, at first glance at least, impossible to negotiate. To his left as he faced outward, the shelf came to an end several meters short of the chimney; in the opposite direction it extended farther, but its end was quite visible.
“Is the gas going to get this high?” he asked.
“Not as long as it flows this way. The gas lake, I judge, is now emptying smoothly.”
“Then maybe its level will go down as it empties,” the man hoped aloud.
“Maybe. I have no basis for estimating its total volume. It seems obvious that it is fed by glaciers of alternating layers of water ice, flowing under pressure even at farside temperatures, and carbon dioxide ice, deposited in alternate seasons. No numbers are available, I fear.”
Faivonen got wearily to his feet; there seemed nothing to do but make really sure about other ways off the ledge. Fifteen minutes later he settled to the same spot with a grunt of greater weariness. No ways up, and the only ones down all led into the gas.
