from perihelion. The angular distance the earth travels in three months. Slightly over one million miles from the sun's center. Six hundred thousand miles from the photosphere. Well within anyone's definition of the corona; within reach of a really healthy eruptive prominence, had any been in the way. One hour and eighteen minutes from their closest approach — or deepest penetration, if one preferred to put it that way. Few did.
They were hurtling, at some three hundred ten miles per second, into a region where the spectroscope claimed temperatures above two million degrees to exist, where ions of iron and nickel and calcium wandered about with a dozen and more of their electrons stripped away, and where the electrons themselves formed almost a gas in their own right, albeit a highly tenuous one.
It was that lack of density on which the men were counting. A single ion at a “temperature” of two million degrees means nothing; there isn't a human being alive who hasn't been struck by vast numbers of far more energetic particles. No one expected to pick up any serious amount of heat from the corona itself.
The photosphere was another matter. It was an opaque, if still gaseous, “surface” which they would approach within one hundred fifty thousand miles — less than its own diameter by a healthy factor. It had a radiation equilibrium temperature of some six thousand degrees, and would fill a large solid angle of sky; this meant that black-body equilibrium temperature at their location would not be much below the same value. The comet, of course, was not a black body — and did not retain even the heat which it failed to reflect. The moment a portion of its surface was warmed seriously, that portion evaporated, taking the newly acquired heat energy with it. A new layer, still only a few degrees above absolute zero, was exposed in its turn to the flood of radiation.
That flood was inconceivably intense, of course; careless, nonquantitative thought could picture the comet's vanishing under that bombardment like a snowball in a blast furnace — but the flood wasn't infinite. A definite, measurable amount of energy struck the giant snowball; a definite amount was reflected; a definite, measurable amount was absorbed and warmed up and boiled away the ices of water and ammonia and methane that made it up.
And there was a lot to boil away. Thrust-acceleration ratios had long ago given the scientists the mass of their shelter, and even at a hundred and fifty thousand miles a two-and-a-half-mile-thick bar of sunlight will take some time to evaporate thirty-five billion tons of ice. The comet would spend only a little over twenty-one hours within five million miles of the sun, and unless several physicists had misplaced the same decimal point, it should last with plenty to spare. The twelve-hour rule on Sacco's echo sounder had been canceled now, and its readings were common knowledge; but none of them caused anxiety.
In they drove. No one could see out, of course; there was nothing like the awed watching of an approaching prominence or gazing into the deceptively pitlike area of a sunspot of which many of them had unthinkingly dreamed. If they could have seen a sunspot at all, it would have been as blinding as the rest of the photosphere — human eyes couldn't discriminate between the two orders of overload. For all any of them knew, they might be going through a prominence at any given second; they wouldn't be able to tell until the instrument records were developed and reduced. The only people who could “see” in any sense at all were the ones whose instruments gave visible as well as recorded readings. Photometers and radiometers did convey a picture to those who understood them; magnetometers and ionization gauges and particle counters meant almost as much; but spectrographs and interferometers and cameras hummed and clicked and whirred without giving any clues to the nature of the meals they were digesting. The accelerometers claimed their share of watchful eyes — if there were any noticeable drag to the medium outside, all bets on the comet's future and their own were off — but nothing had shown so far.
They were nineteen minutes from perihelion when a growing sense of complacency was rudely shattered. There was no warning — one could hardly be expected at three hundred twenty-five miles a second.
One instant they were floating at their instruments, doing their allotted work, at peace with the universe; the next there was a violent jolt, sparks flew from exposed metal terminals, and every remote indicator in the vessel went dead.
For a moment there was silence; the phenomenon ended as abruptly as it had started. Then there was a mixed chorus of yells, mostly of surprise and dismay, a few of pain. Some of the men had been burned by spark discharges. One had also been knocked out by an electric shock, and it was fortunate that the emergency lights had not been affected; they sprang automatically to life as the main ones failed, and order was quickly restored. One of the engineers applied mouth-to-mouth respiration to the shock victim — aesthetic or not, it is the only sort practical in the weightless condition — and each of the scientists began trouble shooting.
None of the remote gear registered in any way, but much of the apparatus inside the ship was still functioning, and a tentative explanation was quickly reached.
“Magnetic field,” was Mallion's terse comment, “size impossible to tell, just as impossible to tell what formed or maintained it. We went through it at three hundred twenty miles a second, plus. If this ship had been metal, it would probably have exploded; as it was, this general sort of thing was a considered possibility and there are no long conducting paths anywhere in the ship — except the instrument controls. The field intensity was between ten and a hundred Gauss. We've taken all the outside readings we're going to, I'm afraid.”
“But we can't stop now!” howled Donegan. “We need pictures — hundreds more of them. How do we correlate all the stuff we have, and the things that will still show on the inside instruments we can still use, unless there are pictures — it's fine to say that this or that or the other thing comes from a prominence, or a flare, or what have you, but we won't know it does, or anything about the size of the flare…”
“I understand, sympathize, and agree; but what do you propose to do about it? I'd bet a small but significant sum that the cable coming in through the access tunnel did explode. Something certainly stopped the current surge before all the instruments here burned up.”
“Come on, Dr. Donegan. Get your suit.” It was Ries, of course. The physicist looked at him, must have read his mind, and leaped toward his locker.
“What are you madmen up to?” shouted Mallion. “You can't go out to that camera — you'd be a couple of moths in a candle flame, to put it mildly!”
“Use your brain, not your thalamus, Doc,” Ries called over his shoulder. Welland said nothing. Two minutes later the pair of madmen were in the air lock, and sixty seconds after that were floating as rapidly as they dared out the tunnel.
The lights were out, but seeing was easy. There was plenty of illumination from the mouth of the tunnel, crooked as the passage was; and the two had to use the filters on their face plates long before they reached the opening. By that time, the very snow around them seemed to be glowing — and may very well have been doing just that, since light must have filtered for some distance in through the packed crystalloids as well as bounced its way around the tunnel bends.
Ries had left his foil shelters at the first bend. There was some loose snow still on hand from his earlier experiments, and they stuffed as much of this as they could between the thin metal layers, and took several of the sandwiched slabs with them as they gingerly approached the opening. They held one of the larger of these — about four feet square — ahead of them as they went; but it proved insufficient when they got within a few yards of the mouth. The trouble was not that the shield failed, but that it wasn't big enough; no matter how close to the opening they came, the entire sky remained a sea of flame. They retreated a little way and Ries rapidly altered the foil armor, bending the sheets and wiring them together until he had a beehive-shaped affair large enough to shield a man. He used the last of then-snow in this assembly.
Covered almost completely, he went alone to the tunnel mouth, and this time he had no trouble. He was able to use a loop of control wire as a safety, and by hooking his toes under this reached the instrument. It had settled quite a bit — its case and mounting had transmitted heat as planned to the broad silver feet, and these had maintained good surface contact. Naturally a good deal of comet material had boiled away from under them, and the whole installation was in a pit over two feet deep and eight in width. The general lowering of the comet's surface was less obvious.
The vanes of the legs were faintly well sunk into the surface, but with gravity as it was, the only difficulty in freeing them was the perennial one — the risk of giving too much upward momentum. Ries avoided this, got camera and mounting loose, and as quickly as possible brought them back into the tunnel. There was no need to disconnect the control wire from the main cable; as Mallion had predicted, both had disappeared. Their explosion had scarred a deep groove along the tunnel wall at several points where they had been close to the side. Ries regretted their loss; without them he had some difficulty getting himself and his burden started downward, and he wanted the camera into the tunnel's relative shelter as quickly as possible. With its heat-shedding “feet” out of
