Complete Short Fiction, page 106
Shandara and Ridging stuck to the relatively dust-free slopes, therefore. The going was easy enough for experienced men, and they traveled at pretty fair speed—some ten or twelve miles an hour, they judged. The tractor soon disappeared, and compasses were useless, but both men had a good eye for country, and were used enough to the Lunar landscape to have no particular difficulty in finding distinctive features. They said little, except to call each other’s attention to particularly good landmarks.
The general ground level was going up after the first hour and a half, though there was still plenty of downhill travel. A relatively near line of peaks ahead was presumably the crater rim; there was little difficulty in deciding on the most suitable one and heading for it. Naturally the footing became worse and the slopes steeper as they approached, but nothing was dangerous even yet. Such crevasses as existed were easy both to see and to jump, and there are few loose rocks on the moon.
It was only about three and a half hours after leaving the tractor, therefore, that the two men reached the peak they had selected, and looked out over the great walled plain of Plato. They couldn’t see all of it, of course; Plato is a hundred kilometers across, and even from a height of two thousand meters the farther side of the floor lies below the horizon. The opposite rim could be seen but there was no easy way to tell whether any of the peaks visible there were as high as the one from which the men saw them. It didn’t really matter; this one was high enough for their purposes.
The instruments were unloaded and set up in half an hour. Ridging did most of the work, with a professional single-mindedness which Shandara made no attempt to emulate. The geophysicist scarcely glanced at the crater floor after his first look around upon their arrival, while Shandara did little else. Ridging was not surprised; he had been reasonably sure that his friend had had ulterior reasons for wanting to come this way.
“All right,” he said, as he straightened up after closing the last switch, “when do we go down, and how long do we take?”
“Go down where?” asked Shandara innocently.
“Down to the crater floor, I suppose. I’m sure you don’t see enough to satisfy you from here. It’s just an ordinary crater, of course, but it’s three times the diameter of Harpalus even if the walls are less than half as high, and you’ll surely want to see every square meter of the floor.”
“I’ll want to see some of the floor, anyway.” Shandara’s tone carried feeling even through the suit radios. “It’s nice of you to realize that we have to go down. I wish you realized why.”
“You mean . . . you mean you really expect to climb down there?” Ridging, in spite of his knowledge of the other’s interests, was startled. “I didn’t really mean—”
“I didn’t think you did. You haven’t looked over the edge once.”
Ridging repaired the omission, letting his gaze sweep carefully over the grayish plain at the foot of the slope. He knew that the floor of Plato was one of the darker areas on the moon, but had never supposed that this fact constituted a major problem.
“I don’t get it,” he said at last. “I don’t see anything. The floor is smoother than that of Harpalus, I’d say, but I’m not really sure even of that, from this distance. It’s a couple of kilos down and I don’t know how far over.”
“You brought the map.” It was not a question.
“Of course.”
“Look at it. It’s a good one.” Ridging obeyed, bewildered. The map was good, as Shandara had said; its scale was sufficient to show Plato some fifteen centimeters across, with plenty of detail. It was basically an enlargement of a map published on Earth, from telescopic observations; but a good deal of detail had been added from photographs taken during the approach and landing of the expedition. Shandara knew that; it was largely his own work.
As a result, Ridging was not long in seeing what his companion meant. The map showed five fairly large craterlets within Plato, and nearly a hundred smaller features.
Ridging could see none of them from where he stood.
He looked thoughtfully down the slope, then at the other man.
“I begin to see what you mean. Did you expect something like this? Is that why you wanted to come here? Why didn’t you tell me?”
“I didn’t expect it, though I had a vague hope. A good many times in the past, observers have reported that the features on the floor of this crater were obscured. Dr. Pickering, at the beginning of the century, thought of it as an active volcanic area; others have blamed the business on clouds—and others, of course, have assumed the observers themselves were at fault, though that is pretty hard to justify. I didn’t really expect to get a chance to check up on the phenomenon, but I’m sure you don’t expect me to stay up here now.”
“I suppose not.” Ridging spoke in a tone of mock resignation. The problem did not seem to concern his field directly, but he judged rightly that the present situation affected Shandara the way an offer of a genuine fragment of Terrestrial core material would influence Ridging himself. “What do you plan to take down? I suppose you want to get measures of some sort.”
“Well, there isn’t too much here that will apply, I’m afraid. I have my own camera and some filters, which may do some good. I can’t see that the magnetic stuff will be any use down there. We don’t have any pressure measuring or gas collecting gadgetry; I suppose if we’d brought a spare water container from the tractor we could dump it, but we didn’t and I’d bet that nothing would be found in it but water vapor if we did. We’ll just have to go down and see what our eyes will tell us, and record anything that seems recordable on film. Are you ready?”
“Ready as I ever will be.” Ridging knew the remark was neither original nor brilliant, but nothing else seemed to fit.
The inner wall of the crater was a good deal steeper than the one they had climbed, but still did not present a serious obstacle. The principal trouble was that much of the way led through clefts where the sun did not shine, and the only light was reflected from distant slopes. There wasn’t much of it, and the men had to be careful of their footings—there was an occasional loose fragment here, and a thousand-meter fall is no joke even on the moon. The way did not lead directly toward the crater floor; the serrated rim offered better ways between its peaks, hairpinning back and forth so that sometimes the central plain was not visible at all. No floor details appeared as they descended, but whatever covered them was still below; the stars, whenever the mountains cut off enough sidelight, were clear as ever. Time and again Shandara stopped to look over the great plain, which seemed limitless now that the peaks on the farther side had dropped below the horizon, but nothing in the way of information rewarded the effort.
It was the last few hundred meters of descent that began to furnish something of interest. Shandara was picking his way down an unusually uninviting bit of slope when Ridging, who had already negotiated it, spoke up sharply.
“Shan! Look at the stars over the northern horizon! Isn’t there some sort of haze? The sky around them looks a bit lighter.” The other paused and looked.
“You’re right. But how could that be? There couldn’t suddenly be enough air at this level—gases don’t behave that way. Van Maanen’s star might have an atmosphere twenty meters deep, but the moon doesn’t and never could have.”
“There’s something between us and the sky.”
“That I admit; but I still say it isn’t gas. Maybe dust—”
“What would hold it up? Dust is just as impossible as air.”
“I don’t know. The floor’s only a few yards down—let’s not stand here guessing.” They resumed their descent.
The crater floor was fairly level, and sharply distinguished from the inner slope of the crater wall. Something had certainly filled, partly at least, the vast pit after the original explosion; but neither man was disposed to renew the argument about the origin of Lunar craters just then. They scrambled down the remaining few yards of the journey and stopped where they were, silently.
There was something blocking vision; the horizon was no longer visible, nor could the stars be seen for a few degrees above where it should have been. Neither man would have had the slightest doubt about the nature of the obscuring matter had he been on Earth; it bore every resemblance to dust. It had to be dust.
But it couldn’t be. Granted that dust can be fine enough to remain suspended for weeks or months in Earth’s atmosphere when a volcano like Krakatoa hurls a few cubic miles of it aloft, the moon had not enough gas molecules around it to interfere with the trajectory of a healthy virus particle—and no seismometer in the last four weeks had registered crustal activity even approaching the scale of vulcanism. There was nothing on the moon to throw the dust up, and even less to keep it there.
“Meteor splash?” Shandara made the suggestion hesitantly, fully aware that while a meteor might raise dust it could never keep it aloft. Ridging did not bother to answer, and his friend did not repeat the suggestion.
The sky straight overhead seemed clear as ever; whatever the absorbing material was it apparently took more than the few feet above them to show much effect. That could not be right, though, Ridging reflected, if this stuff was responsible for hiding the features which should have been visible from the crater rim. Maybe it was thicker farther in. If so, they’d better go on—there might be some chance of collecting samples after all.
He put this to Shandara, who agreed; and the two started out across the hundred kilometer plain.
The surface was fairly smooth, though a pattern of minute cracks suggestive of the joints formed in cooling basalt covered it almost completely. These were not wide enough even to constitute a tripping danger, and the men ignored them for the time being, though Ridging made a mental note to get a sample of the rock if he could detach one.
The obscuration did thicken as they progressed, and by the time they had gone half a dozen kilometers it was difficult to see the crater wall behind them. Looking up, they saw that all but the brighter stars had faded from view even when the men shaded their eyes from the sunlit rock around them.
“Maybe gas is coming from these cracks, carrying dust up with it?” Shandara was no geologist, but had an imagination. He had also read most of the serious articles which had ever been published about the moon.
“We could check. If that were the case, it should be possible to see currents coming from them; the dust would be thicker just above a crack than a few centimeters away. If we had something light, like a piece of paper, it might be picked up.”
“Worth trying. We have the map,” Shandara pointed out. “That should do for paper; the plastic is thin enough.” Ridging agreed. With some difficulty—spacesuit gloves were not designed for that purpose—he tore a tiny comer off the sheet on which the map was printed, knelt down, and held the fragment over one of the numerous cracks. It showed no tendency to flutter in his grasp, and when he let go it dropped as rapidly as anything ever did on the moon, to lie quietly directly across the crack he had been testing. He tried to pick it up, but could not get a grip on it with his stiff gloves.
“That one didn’t seem to pan out,” he remarked, standing up once more.
“Maybe the paper was too heavy—this stuff must be awfully fine—or else it’s coming from only a few of the cracks.”
“Possibly; but I don’t think it’s practical to try them all. It would be smarter to figure some way to get a sample of this stuff, and let people with better lab facilities figure out what it is and what holds it off the surface.”
“I’ve been trying to think of a way to do that. If we laid the map out on the ground, some of the material might settle on it.”
“Worth trying. If it does, though, we’ll have another question—why does it settle there and yet remain suspended long enough to do what is being done? We’ve been more than an hour coming down the slope, and I’ll bet your astronomical friends of the past have reported obscurations longer lasting even than that.”
“They have. Well, even if it does raise more problems it’s worth trying. Spread out the map, and we’ll wait a few minutes.” Ridging obeyed; then, to keep the score even, came up with an idea of his own.
“Why don’t you lay your camera on the ground pointing up and make a couple of time exposures of the stars? You could repeat them after we get back in the clear, and maybe get some data on the obscuring power of this material.”
“Good enough.” Shandara removed the camera from its case, clipped a sun shade over its lens, and looked up to find a section of sky with a good selection of stars. As usual, he had to shield his eyes both from sunlight and from the glare of the nearby hills; but even then he did not seem satisfied.
“This stuff is getting thicker, I think,” he said. “It’s scattering enough light so that it’s hard to see any stars at all—harder than it was a few minutes ago, I’d say,” Ridging imitated his maneuver, and agreed.
“That’s worth recording, too,” he pointed out. “Better stay here a while and get several shots at different times.” He looked down again. “It certainly is getting thicker. I’m having trouble seeing you, now.”
Human instincts being what they are, the solution to the mystery followed automatically and immediately. A man who fails, for any reason, to see as clearly as he expects usually rubs his eyes—if he can get at them. A man wearing goggles or a space helmet may just possibly control this impulse, but he follows the practically identical one of wiping the panes through which he looks. Ridging did not have a handkerchief within reach, of course, and the gauntlet of a spacesuit is not one of the best windshield wipers imaginable; but without giving a single thought to the action, he wiped his face plate with his gauntlet.
Had there been no results he would not have been surprised; he had no reason to expect any. He would probably have dismissed the matter, perhaps with a faint hope that his companion might not have noticed the futile gesture. However, there were results. Very marked ones.
The points where the plastic of the gauntlet actually touched the face plate were few; but they left trails all the way across—opaque trails. Surprised and still not thinking, Ridging repeated the gesture in an automatic effort to wipe the smears of whatever it was from his helmet; he only made matters worse. He did not quite cover the supposedly transparent area with glove trails—but in the few seconds after he got control of his hand the streaks spread and merged until nothing whatever was visible. He was not quite in darkness; sunlight penetrated the obscuring layer, but he could not see any details.
“Shan!” The cry contained almost a note of panic. “I can’t see at all. Something’s covering my helmet!” The cartographer straightened up from his camera and turned toward his friend.
“How come? You look all right from here. I can’t see too clearly, though—”
Reflexes are wonderful. It took about five seconds to blind Shandara as thoroughly as Ridging. He couldn’t even find his camera to close the shutter.
“You know,” said Ridging thoughtfully after two or three minutes of heavy silence, “we should have been able to figure all this out without coming down here.”
“Why?”
“Oh, it’s plain as anything—”
“Nothing, and I mean nothing, is plain right now.”
“I suppose a map maker would joke while he was surveying Gehenna. Look, Shan, we have reason to believe there’s a magnetic storm going on, which strongly suggests charged particles from the sun. We are standing, for practical purposes, on the moon’s south magnetic pole. Most level parts of the moon are covered with dust—but we walked over bare rock from the foot of the rim to here. Don’t those items add up to something?”
“Not to me.”
“Well, then, add the fact that electrical attraction and repulsion are inverse square forces like gravity, but involve a vastly bigger proportionality constant.”
“If you’re talking about scale I know all about it, but you still don’t paint me a picture.”
“All right. There are, at a guess, protons coming from the sun. They are reaching the moon’s surface here—virtually all of them, since the moon has a magnetic field but no atmosphere. The surface material is one of the lousiest imaginable electrical conductors, so the dust normally on the surface picks up and keeps a charge. And what, dear student, happens to particles carrying like electrical charges?”
“They are repelled from each other.”
“Head of the class. And if a hundred-kilometer circle with a rim a couple of kilos high is charged all over, what happens to the dust lying on it?”
Shandara did not answer; the question was too obviously rhetorical. He thought for a moment or two, instead, then asked, “How about our face plates?”
Ridging shrugged—a rather useless gesture, but the time for fighting bad habits had passed some minutes before.
“Bad luck. Whenever two materials rub against each other, electrons come loose. Remember your rubber-and-cat-fur demonstrations in grade school. Unless the materials are of identical electronic make-up, which for practical purposes means unless they are the same substance, one of them will hang onto the electrons a little—or a lot—better than the other, so one will have a negative net charge and the other a positive one. It’s our misfortune that the difference between the plastic in our face plates and that in the rest of the suits is the wrong way; when we rubbed the two, the face plates picked up a charge opposite to that of the surrounding dust—probably negative, since I suppose the dust is positive and a transparent material should have a good grip on its electrons.
