Some of the little pots were full; most of these appeared to be unchanged. Others, however, were not. The contents of most of these were easy to find, but Ken could see that they were going to be hard to identify.
A white powder was literally over everything, as Roger had already seen. The yellow flecks of sodium peroxide were turning grayish as they decomposed in the heat. The gold crucible had been pulled from its base, but was otherwise unchanged; the iron had turned black; sodium, magnesium and titanium had disappeared, though the residue in each crucible gave promise that some of the scattered dust could be identified. There was still carbon in the container devoted to that substance, but much less of it than there had been.
All these things, however, interesting and important as they might be, only held the attention of Feth and Ken for a moment; for just inside the cargo door, imprinted clearly in the layer of dust, was a mark utterly unlike anything either had ever seen.
“Feth, dig up a camera somewhere. I’m going to get Drai.” Ken was gone almost before the words had left his diaphragm, and for once Feth had nothing to say. His eyes were stall fixed on the mark.
There was nothing exactly weird or terrifying about it; but he was utterly unable to keep his mind from the fascinating problem of what had made it. To a creature which had never seen anything even remotely like a human being, a hand print is apt to present difficulties in interpretation. For all he could tell, the creature might have been standing, sitting, or leaning on the spot, or sprawled out in the manner the Sarrians substituted for the second of those choices. There was simply no telling; the native might be the size of a Sarrian foot, making the mark with his body — or he might have been too big to get more than a single appendage into the compartment. Feth shook his head to clear it — even he began to realize that his thoughts were beginning to go in circles. He went to look for a camera.
Sallman Ken burst into the observatory without warning, but gave Drai no chance to explode. He was bursting himself with the news of the discovery — a little too much, in fact, since he kept up the talk all the way back to the shop. By the time they got there, the actual sight of the print was something of an anticlimax to Drai. He expressed polite interest, but little more. To him, of course, the physical appearance of Earth’s natives meant nothing whatever. His attention went to another aspect of the compartment.
“What’s all that white stuff?”
“I don’t know yet,” Ken admitted. “The torpedo just got back. It’s whatever Planet Three’s atmosphere does to the samples I sent down.”
“Then you’ll know what the atmosphere is before long? That will be a help. There are some caverns near the dark hemisphere that we’ve known about for years, which we could easily seal off and fill with whatever you say. Let us know when you find out anything.” He drifted casually out of the shop, leaving Ken rather disappointed. It had been such a fascinating discovery.
He shrugged the feeling off, collected what he could of his samples without disturbing the print, and bore them across the room to the bench on which a makeshift chemical laboratory had been set up. As he himself had admitted, he was not an expert analyst; but compounds formed by combustion were seldom extremely complex, and he felt that he could get a pretty good idea of the nature of these. After all, he knew the metals involved — there could be no metallic gases except hydrogen in Planet Three’s atmosphere. Even mercury would be a liquid, and no other metal had a really high vapor pressure even at Sarrian temperature. With this idea firmly in mind like a guiding star, Ken set blithely to work.
To a chemist, the work or a description of it would be interesting. To anyone else, it would be a boringly repetitious routine of heating and cooling, checking for boiling points and melting points, fractionating and filtering. Ken would have been quicker had he started with no preconceived notions; but finally even he was convinced. Once convinced, he wondered why he had not seen it before.
Feth Allmer had returned long since, and photographed the hand print from half a dozen angles. Now, seeing that Ken had stopped working, he roused himself from the rack on which he had found repose and approached the work bench.
“Have you got it, or are you stumped?” he queried.
“I have it, I guess. I should have guessed long ago. It’s oxygen.”
“What’s so obvious about that? Or, for that matter, why shouldn’t it be?”
“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.”
“Just one trouble,” put in Feth. “Do we have an echo-sounder? Like Ken on his soil analysis, I have my doubts about being able to make one.” Nobody answered that for some moments.
“I guess I’d better show you some of the other caves we’ve found already,” Lee said at last. No one objected to this, and they retraced their steps to daylight. In the next four hours they looked at seven more caves, ranging from a mere hemispherical hollow in the very face of the cliff to a gloomy, frighteningly deep bubble reached by a passageway just barely negotiable for a space-suited Sarrian. This last, in spite of the terrors of its approach and relative smallness, was evidently the best for their purpose out of those examined; and Lee made a remark to that effect as they doffed space suits back in the Karella.
“I suppose you’re right,” Ken admitted, “but I’d still like to poke deeper. Blast it, Feth, are you sure you couldn’t put a sounder together? You never had any trouble with the gadgets we used in the torpedoes.”
“Now you’re the one who doesn’t realize the problem,” the mechanic replied. “We were using heating coils, thermometers, pressure gauges, and photocells for the other stuff. Those come ready made. All I did was hook them up to a regular achronic transmitter — we couldn’t use ordinary radio because the waves would have taken ten or twelve minutes for the round trip. I didn’t make anything — just strung wires.”
“I suppose you’re right,” Ken admitted. “In that case, we may as well go back to the station and lay plans for sealing off that last cavern.” He kept a sharp look on his two companions as he said this, and succeeded in catching the glance Feth sent at the clock before his reply. It almost pleased him.
“Hadn’t we better get some photographs and measurements of the cave first?” Ordon Lee cut in. “We’ll need them for estimates on how much gas and soil will be needed, regardless of how it’s to be obtained.” Ken made no objection to this; there was no point in raising active suspicion, and he had substantiated his own idea. He was being kept away from the station intentionally. He helped with the photography, and subsequently with the direct measurement of the cave. He had some trouble refraining from laughter; affairs were so managed that the party had returned to the ship and doffed space suits each time before the next activity was proposed. It was very efficient, from one point of view. Just to keep his end up, he proposed a rest before returning to the base, and was enthusiastically seconded by the others. Then he decided to compute the volume of the cave from their measurements, and contrived to spend a good deal of time at that — legitimately, as the cave was far from being a perfect sphere. Then he suggested getting some samples of local rock to permit an estimate of digging difficulties, and bit back a grin when Feth suggested rather impatiently that that could wait. Apparently he had outdone the precious pair at their own game — though why Feth should care whether or not they stayed longer than necessary was hard to see.
“It’s going to take quite a lot of gas,” he said as the Karella lunged into the black sky. “There’s about two million cubic feet of volume there, and even the lower pressure we need won’t help much. I’d like to find out if we can get oxygen from those rocks; we should have picked up a few samples, as I suggested. We’re going to have to look over the upper area for small cracks, too— we have no idea how airtight the darn thing is. I wish we could — say, Feth, aren’t there a lot of radar units of one sort or another around here?”
“Yes, of course. What do you want them for? Their beams won’t penetrate rock.”
“I know. But can’t the pulse-interval on at least some of them be altered?”
“Of course. You’d have to use a different set every time your range scale changed, otherwise. So what?”
“Why couldn’t we — or you, anyway — set one up with the impulse actuating a sounder of some sort which could be put in contact with the rock, and time that return-echo picked up by a contact-mike? I know the impulse rate would be slower, but we could calibrate it easily enough.”
“One trouble might be that radar units are usually not very portable. Certainly none of the warning devices in this ship are.”
“Well, dismantle a torpedo, then. They have radar altimeters, and there are certainly enough of them so one can be spared. We could have called base and had them send one out to us — I bet it would have taken you only a few hours. Let’s do that anyway — we’re still a lot closer to the caves than to the base.”
“It’s easier to work in the shop; and anyway, if we go as far underground as this idea should let us — supposing it works — we might as well scout areas closer to the base, for everyone’s convenience.” Ordon Lee contributed the thought without looking from his controls.
“Do you think you can do it?” Ken asked the mechanic.
“It doesn’t seem too hard,” the latter answered. “Still, I don’t want to make any promises just yet.”
“There’s a while yet before that suit comes back. We can probably find out before then, and really have some material for Drai to digest. Let’s call him now — maybe he’ll have some ideas about soil.”
The eyes of the other two met for a brief moment; then Lee gestured to the radio controls,
“Go ahead; only we’ll be there before you can say much.”
“He told me you were going to manufacture soil,” reminded Feth.
“I know. That’s why I want to talk to him — we left in too much of a hurry before.” Ken switched on the radio while the others tried to decide whether or not he was suspicious about that hasty departure. Neither dared speak, with Ken in the same room, but once again their eyes met, and the glances were heavy with meaning.
Drai eventually came to the microphone at the other end and Ken began talking with little preliminary.
“We’ve made measurements of the smallest cave we can find, so far at least, and figured out roughly how much air you’re going to need to fill it. I can tell you how much soil you’ll need to cover the bottom, too, if you plan to use all of it. The trouble is, even if I can analyze the soil — even as roughly as I did the air — you’re facing a supply problem that runs into tons. I can’t make that much in the laboratory in any reasonable time. You’re going to have to get it ready-made.”
“How? We can’t land a person on Planet Three, let alone a freighter.”
“That we’ll see presently. But that’s not the suggestion I wanted to make — I see we’re nearly there, so we can finish this chat in person. Think this over while we’re going in: whatever sort of atmosphere a planet may have, I don’t see how the soils can be too different — at least in their principal constituents. Why don’t you get a shipload of Sarrian soil?” Drai gaped for a moment.
“But — bacteria—”
“Don’t be silly; nothing Sarrian could live at that temperature. I admit it would be safer to use soil from Planet Three, and we may be able to. But if we can’t, then you have my advice, if you’re interested in speed — even if I knew the composition, it would take me a lot longer than a week to make a hundred tons of dirt!” He broke the connection as the Karella settled to the ground.