The trouble was that he could do very little more here than he could in the tractor. He could have improvised longer-wave transmitting coils whose radiations would have diffracted a little more effectively beyond the horizon, but the receiver on the missing vehicle would not have detected them. He had more power at his disposal, but could only beam it into empty space with his better antennae. He had better equipment for locating any projecting wisps of charged gas which might reflect his waves, but he was already located under a solid roof of the stuff—the Albireo was technically on Brightside. Bouncing his beam from this layer still didn’t give him the range he needed, as he had found both by calculation and trial.
What he really needed was a relay satellite. The target was simply too far around Mercury’s sharp curve by now for anything less.
Zaino’s final gesture was to set his transmission beam on the lowest frequency the tractor would pick up, aim it as close to the vehicle’s direction as he could calculate from map and itinerary and set the recorded return message going. He told Rowson as much.
“Can’t think of anything else?” the captain asked. “Well neither can I, but of course it’s not my field. I’d give a year’s pay if I could. How long before they should be back in range?”
“About four days. A hundred hours, give or take a few. They’ll be heading back anyway by that time.”
“Of course. Well, keep trying.”
“I am—or rather, the equipment is. I don’t see what else I can do unless a really bright idea should suddenly sprout. Is there anywhere else I could be useful? I’m as likely to have ideas working as just sitting.”
“We can keep you busy, all right. But how about taking a transmitter up one of those mountains? That would get your wave farther.”
“Not as far as it’s going already. I’m bouncing it off the ion layer, which is higher than any mountain we’ve seen on Mercury even if it’s nowhere near as high as Earth’s.”
“Hmph. All right.”
“I could help Ren and Dr. Burkett, I could hang on outside the tractor—”
“They’ve already gone. You’d better call them, though, and keep a log of what they do.”
“All right,” Zaino turned back to his board and with no trouble raised the tractor carrying Hargedon and the mineralogist. The latter had been trying to call the Albireo and had some acid comments about radio operators who slept on the job.
“There’s only one of me, and I’ve been trying to get the Darkside team,” he pointed out. “Have you found anything new about this lava flood?”
“Flow, not flood,” corrected the professional automatically. “We’re not in sight of it yet. We’ve just rounded the corner that takes us out of your sight. It’s over a mile yet, and a couple of more corners, before we get to the spot where I left it. Of course, it will be closer than that by now. It was spreading at perhaps a hundred yards an hour then. That’s one figure we must refine. Of course, I’ll try to get samples, too. I wish there were some way to get samples of the central cone. The whole thing is the queerest volcano I’ve ever heard of. Have you gotten Eileen started back?”
“Not as far as I can tell. As with your cone samples, there are practical difficulties,” replied Zaino. “I haven’t quit yet, though.”
“I should think not. If some of us were paid by the idea we’d be pretty poor, but the perspiration part of genius is open to all of us.”
“You mean I should charge a bonus for getting this call through?” retorted the operator.
Whatever Burkett’s reply to this might have been was never learned; her attention was diverted at that point.
“We’ve just come in sight of the flow. It’s about five hundred yards ahead. We’ll get as close as seems safe, and I’ll try to make sure whether it’s really lava or just mud.”
“Mud? Is that possible? I thought there wasn’t—couldn’t be—any water on this planet!”
“It is, and there probably isn’t. The liquid phase of mud doesn’t have to be water, even though it usually is on Earth. Here, for example, it might conceivably be sulfur.”
“But if it’s just mud, it wouldn’t hurt the ship, would it?”
“Probably not.”
“Then why all this fuss about getting the tractors back in a hurry?”
The voice which answered reminded him of another lady in his past, who had kept him after school for drawing pictures in math class.
“Because in my judgment the flow is far more likely to be lava than mud, and if I must be wrong I’d rather my error were one that left us alive. I have no time at the moment to explain the basis of my judgment. I will be reporting our activities quite steadily from now on, and would prefer that you not interrupt unless a serious emergency demands it, or you get a call from Eileen.
“We are about three hundred yards away now. The front is moving about as fast as before, which suggests that the flow is coming only along this valley. It’s only three or four feet high, so viscosity is very low or density very high. Probably the former, considering where we are. It’s as black as the smoke column.”
“Not glowing?” cut in Zaino thoughtlessly.
“Black, I said. Temperature will be easier to measure when we get closer. The front is nearly straight across the valley, with just a few lobes projecting ten or twelve yards and one notch where a small spine is being surrounded. By the way, I trust you’re taping all this?” Again Zaino was reminded of the afternoon after school.
“Yes, Ma’am,” he replied. “On my one and only monitor tape.”
“Very well. We’re stopping near the middle of the valley one hundred yards from the front. I am getting out, and will walk as close as I can with a sampler and a radiometer. I assume that the radio equipment will continue to relay my suit broadcast back to you.” Zaino cringed a little, certain as he was that the tractor’s electronic apparatus was in perfect order.
It struck him that Dr. Burkett was being more snappish than usual. It never crossed his mind that the woman might be afraid.
“Ren, don’t get any closer with the tractor unless I call. I’ll get a set of temperature readings as soon as I’m close enough. Then I’ll try to get a sample. Then I’ll come back with that to the tractor, leave it and the radiometer and get the markers to set out.”
“Couldn’t I be putting out the markers while you get the sample, Doctor!”
“You could, but I’d rather you stayed at the wheel.” Hargedon made no answer, and Burkett resumed her description for the record.
“I’m walking toward the front, a good deal faster than it’s flowing toward me. I am now about twenty yards away, and am going to take a set of radiation-temperature measures.” A brief pause. “Readings coming. Nine sixty. Nine eighty. Nine ninety—that’s from the bottom edge near the spine that’s being surrounded. Nine eighty-five—” The voice droned on until about two dozen readings had been taped. Then, “I’m going closer now. The sampler is just a ladle on a twelve-foot handle we improvised, so I’ll have to get that close. The stuff is moving slowly; there should be no trouble. I’m in reach now. The lava is very liquid; there’s no trouble getting the sampler in—or out again—it’s not very dense, either. I’m heading back toward the tractor now. No, Ren, don’t come to meet me.”
There was a minute of silence, while Zaino pictured the space-suited figure with its awkwardly long burden, walking away from the creeping menace to the relative safety of the tractor. “It’s frozen solid already; we needn’t worry about spilling. The temperature is about—five eighty. Give me the markers, please.”
Another pause, shorter this time. Zaino wondered how much of that could be laid to a faster walk without the ladle and how much to the lessening distance between flow and tractor. “I’m tossing the first marker close to the edge—it’s landed less than a foot from the lava. They’re all on a light cord at ten-foot intervals; I’m paying out the cord as I go back to the tractor. Now we’ll stand by and time the arrival at each marker as well as we can.”