Hal Clement - Iceworld

“To the latter question, no reason. I simply rejected it as a possibility at first because it’s so active. I never stopped to think that it’s little if any more active at that temperature than sulfur is at ours. It’s perfectly possible to have it free in an atmosphere — provided there’s a process constantly replacing what goes into combination. You need the same for sulfur. Blast it, the two elements are so much alike! I should have thought of that right away!”

“What do you mean — a replacement process?”

“You know we breath sulfur and form sulfides with our metabolic processes. Mineral-eating life such as most plants, on the other hand, breaks down the sulfides and releases free sulfur, using solar energy for the purpose. Probably there is a similar division of life forms on this planet — one forming oxides and the other breaking them down. Now that I think of it, I believe there are some micro-organisms on Sarr that use oxygen instead of sulfur.”

“Is it pure oxygen?”

“No — only about a fifth or less. You remember how quickly the sodium and magnesium went out, and what the pressure drop was with them.”

“No, I don’t, and I can’t say that it means much to me anyway, but I’ll take your word for it. What else is there in the atmosphere? The titanium took about all of it, I do remember.”

“Right. It’s either nitrogen or some of its oxides — I can’t tell which without better controlled samples for quantity measurement. The only titanium compounds I could find in that mess were oxides and nitrides, though. The carbon oxidized, I guess — the reason there was no pressure change except that due to heat was that the principal oxide of carbon has two atoms of oxygen, and there is therefore no volume change. I should have thought of that, too.”

“I’ll have to take your word for that, too, I guess. All we have to do, then, is cook up a four-to-one mixture of nitrogen and oxygen and fill the caves the boss mentioned to about two-thirds normal pressure with it?”

“That may be a little oversimplified, but it should be close enough to the real thing to let this tofacco stuff grow — if you can get specimens here alive, to start things off. It would be a good idea to get some soil, too — I don’t suppose that powdering the local rock would help much. I may add in passing that I refuse even to attempt analyzing that soil. You’ll have to get enough to use.” Feth stared.

“But that’s ridiculous! We need tons, for a decent-sized plantation!” Sallman Ken shrugged.

“I know it. I tell you clearly that it will be easier to get those tons than to get an accurate soil analysis out of me. I simply don’t know enough about it, and I doubt if Sarr’s best chemist could hazard a prediction about the chemicals likely to be present in the solid state on that planet. At that temperature, I’ll bet organic compounds could exist without either fluorine or silicon.”

“I think we’d better get Drai back here to listen to that. I’m sure he was planning to have you synthesize both atmosphere and soil, so that we could set up the plantation entirely on our own.”

“Perhaps you’d better. I told him my limitations at the beginning; if he still expects that, he has no idea whatever of the nature of the problem.” Feth left, looking worried, though Ken was unable to understand what particular difference it made to the mechanic. Later he was to find out.

The worried expression was still more evident when Feth returned.

“He’s busy now. He says he’ll talk it over with you after that suit comes back, so that any alternatives can be considered, too. He wants me to take you out to the caves so you can see for yourself what he has in mind for making them usable.”

“How do we get there? They must be some distance from here.”

“Ordon Lee will take us around in the ship. It’s about two thousand miles. Let’s get into our suits.”

Ken heroically swallowed the impulse to ask why the whole subject should have come up so suddenly in the midst of what seemed a totally different matter, and went to the locker where the space suits were stowed. He more than suspected the reason, anyway, and looked confidently forward to having the trip prolonged until after the return of the trading torpedo.

His attention was shifted from these matters as he stepped onto the surface of Mercury, for the first time since his arrival at the station. The blistered, baked, utterly dry expanse of the valley was not particularly strange to him, since Sarr was almost equally dry and even hotter; but the blackness of the sky about the sun and the bareness of the ground contributed to a dead effect that he found unpleasant. On Sarr, plant life is everywhere in spite of the dryness; the plants with which Ken was familiar were more crystalline than organic and needed only the most minute amounts of liquid for their existence.

Also, Sarr has weather, and Mercury does not. As the ship lifted from the valley, Ken was able to appreciate the difference. Mercury’s terrain is rugged, towering and harsh. The peaks, faults and meteor scars are unsoftened by the blurring hand of erosion. Shadows are dark where they exist at all, relieved only by light reflected from nearby solid objects. Lakes and streams would have to be of metals like lead and tin, or simple compounds like the “water” of Sarr — copper chloride, lead bromide, and sulfides of phosphorus and potassium. The first sort are too heavy, and have filtered down through the rocks of Mercury, if they ever existed at all; the second are absent for lack of the living organisms that might have produced them. Sallman Ken, watching the surface over which they sped, began to think a little more highly even of Earth.

A vessel capable of exceeding the speed of light by a factor of several thousand makes short work of a trip of two thousand miles, even when the speed is kept down to a value that will permit manual control. The surface was a little darker where they landed, with the sun near the horizon instead of directly overhead and the shadows correspondingly longer. It looked and was colder. However, the vacuum and the poor conducting qualities of the rock made it possible even here to venture out in ordinary space suits, and within a few moments Ken, Feth and the pilot were afoot gliding swiftly toward a cliff some forty feet in height.

The rock surface was seamed and cracked, like nearly all Mercurian topography. Into one of the wider cracks Lee unhesitatingly led the way. It did not lead directly away from the sun, and the party found itself almost at once in utter darkness. With one accord they switched on their portable lamps and proceeded. The passage was rather narrow at first, and rough enough on both floor and walls to be dangerous to space suits. This continued for perhaps a quarter of a mile, and quite suddenly opened into a vast, nearly spherical chamber. Apparently Mercury had not always been without gases — the cave had every appearance of a bubble blown in the igneous rock. The crack through which the explorers had entered extended upward nearly to its top, and downward nearly as far. It had been partly filled with rubble from above, which was the principal reason the going had been so difficult. The lower part of the bubble also contained a certain amount of loose rock. This looked as though it might make a climb down to the center possible, but Ken did not find himself particularly entranced by the idea.

“Is there just this one big bubble?” he asked. Ordon Lee answered.

“No; we have found several, very similar in structure, along this cliff, and there are probably others with no openings into them. I suppose they could be located by echo-sounders if we really wanted to find them.”

“It might be a good idea to try that,” Ken pointed out. “A cave whose only entrance was one we had drilled would be a lot easier to keep airtight than this thing.” Feth and Lee grunted assent to that. The latter added a. thought of his own. “It might be good if we could find one well down; we could be a lot freer in drilling — there’d be no risk of a crack running to the surface.”