“This stuff appears to be of polar continental origin, judging by its temperature and dryness,” he said. “It’s not extremely cold, but in Hekla’s atmosphere it could still have formed over the polar ice cap, and probably did. On Earth, such a mass couldn’t come anything like this far south in summer. The normal surface circulation is too strong for it, and remains too strong as long as the ground is receiving much solar energy. However, it could be forced down like this if we supposed another, still colder, mass to the east of its source region, against which it was carried by the normal trade circulation and thence deflected southward. Also, a general cooling of the continental areas to the south of the source region might permit it to be carried down here around a normal cyclone.
“Either supposition demands a decrease in ground surface temperature comparable to that experienced at the onset of winter. I can’t imagine any large area waiting until this late in the summer to become covered by snow; but I can’t see any other means of dropping the temperature of a large area to any great extent, unless the axis of the planet shifts enough to decrease insolation in this hemisphere.” He grinned wryly as he made that remark; he realized perfectly well that the application of sufficient force to shift the axis of a major planet would buckle its crust at the very least, and more probably disrupt the world.
“How about night cooling?” asked Vickers. “This planet rotates more slowly than Earth.”
“Not enough; in summer the nights are short anyway; and why would it wait until now, fully two Earth years after midsummer, to take effect?”
“Then how about this mist that seems to have been cutting off some of the sunlight of the last day or two? You must have noticed it — it appears to be above any level at which we’ve flown, so it can’t be very dense; but it seems to be practically planet-wide, and cuts off enough light for me to notice without instruments.”
“I hadn’t noticed it particularly,” said Rodin thoughtfully. “A high layer of water vapor or dust would have a blanketing effect, and would actually increase surface temperature, even though it cut off some visible light. However, there’s something to the idea; the stuff might just possibly have a high reflecting power, I suppose. It won’t hurt us to go up and find this layer, anyway.”
Rodin went back to the controls, and started the ship climbing slowly. Then he started the recorder of the radiograph he had set up at one of the portholes when he had first arrived, and waited while they rose through the thinning atmosphere to a level at which the outside pressure was no longer detectable. There he stopped ship and recorder, and removed the graph from the latter. The haze layer, if it existed, should have betrayed its presence by a more or less sharp break in the curve — or rather, a change in its slope — at the proper level; but Rodin, to his disgust, was unable to find anything of the sort by visual inspection. He was beginning to check the instrument for flaws that would affect its sensitivity, when Vickers remarked that the sun seemed still to be rather weaker than usual — rather as Sol would appear from Earth during a partial eclipse, allowing for the difference in their intrinsic luminosities.
“An eclipse?” queried Rodin. “Hekla has only two satellites big enough and near enough to produce a respectable eclipse; and even the partial phase would last only a few hours. You noticed this dimness a couple of days ago.”
He went to the port and looked up at the sun. From Hekla’s surface the human eye could bear to look directly at R Coronae’s immense disk, but here above the atmosphere it was a little too bright for comfort. He rummaged in a drawer under the control panel, found a pair of shielded goggles; with these he approached the port again, and looked long and earnestly at the fuzzy crimson blot hanging in the blackness of space. At last he called Vickers, gave him the goggles, and asked him to look, describe, and if possible explain what he saw. Vickers obediently donned the eye shields and went to the port.
He had seen red giant suns before — who hadn’t? He was familiar with the brilliant crimson or orange disks, with brightness fading rapidly toward the ill-defined edges, bordered by a faintly luminous rim of atmosphere that faded rapidly outward against the star-shot background of the Galaxy. R Coronae should have been the same.