Iceworld

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.