The river at the moment was a dozen meters away from the parked robot. Carol headed for it, eagerly but with caution bred by the low gravity, took a sample, and made the same standard test she had used on the stream so far above.
“It’s not pure ammonia by a lot,” she reported after a moment. “This gadget makes it about seventy percent. I don’t know what the rest is.”
Molly’s armor lacked comparable testing gear, but she had a thermometer probe. She dipped this into the liquid on her glove and held it away from her suit, watching sample and reading as the substance froze again.
“Just under two seventy-two. Not pure, but mostly water. What’s going on here?”
“What’s the air temperature?” asked Charley.
“Wait a moment—it’s still dropping, now the stuff’s all frozen.” Charley waited, to Carol’s surprise. “About two sixty-four. Check, Carrie?”
“That’s what mine’s been saying.”
“And the river?” Another brief delay while the women made the test.
“About two fifty-five. Much too high for pure ammonia, much too low for water. I couldn’t begin to calculate percentage composition because it’s probably not an equilibrium mixture, I don’t know the constants for either association or ionization in those mixtures, and I certainly don’t know what else may be there. So what’s going on?”
“Very simple,” said Charley. Carol rolled her eyes wildly but managed to keep silent. “There’s heat below, warming the wind that comes up. Liquid is going down. The walls of the caves and passages connecting them give plenty of surface area and are rough enough for all sorts of turbulence. The planet is a countercurrent heat exchanger…”
“Better yet, it’s a reflux condenser!” Molly jumped enthusiastically at the suggestion. Carol, with her conditioned skepticism for Charley-hypotheses, remained silent. “But there goes the last chance of my finding any ice—even water ice—down below. Wouldn’t you say, Joe?”
“I gather you just found some.”
“You know what I mean. Masses of it. Chunks that would explain these caves being kames, not just frost deposits on cold rock from vapor picked up from the river.”
“I’m afraid so. I can’t yet guess how far down the caverns extend, and I don’t know how far down you are. My new robots have mapped downward a little over a hundred and fifty kilometers, but they’re not equipped to take pictures or specimens, and I regret to say they can’t measure temperature.”
“Joe!” Molly hoped that Carol’s shocked tone was not meant seriously. The Nethneen seemed unaffected; at least, he offered no further apology.
“To that depth,” he went on, “the crust remains about the same. Between a quarter and a third of its volume is open space, as measured by the radar of the small units.”
“How do you keep in touch with them for such a distance through rock?” Molly asked.
“I’ve programmed them to spread out in such a way as to be able to relay among themselves and all the way back to me. After the whole set of robots is completed and extended as far as practical, I’m going to have to go underground myself so that they won’t have to use so many units in relay to the surface that their mapping front is too greatly reduced.”
“So they each carry complete diagrams of the volume covered, and so does your own carrier.”
“Right. I’ll be able to follow down very quickly, when the time comes.”
“Fine,” said Molly happily. “Then downward to the warmth of the Underworld. This is starting to be fun. Oh—Carol, how about your armor’s refrigerator? Is it all right? Is there any reason to worry about it? What sort of backup does it have?”
“It’ll work. Standard equipment. No moving parts bigger than electrons to get out of order; I never heard of one failing. And I do wish you’d never given that word worry to my translator. Come along, and even if you can’t help worrying about yourself, stop fretting over me.”
Molly made no answer, though she wondered whether Carol or her own translator had come up with “fret”. She came along.
No one had bothered Jenny for a long time. Joe would not have dreamed of it, since she was presumably working; Molly would not have as long as Joe might notice; Carol had managed to resist by reminding herself that any questions would have made her look too much like Charley; what had held the Kantrick back no one wanted to ask.
When the Rimmore finally did speak, Carol immediately keyed the robot to a stop; she wanted to give full attention.
“There’s obviously a lot yet to check” came the grating tones, “but you’ll all want to hear this much right away. The organisms I picked up represent at least two basically different life forms—that is, different in genetic coding. They are cellular in structure, which is not surprising, since that is the easiest way to engineer the nutrition-in and waste-out problem for any creature above microscopic size. The interesting point is that they do contain high energy compounds, as was suggested. There are hydrazine and hydrazine derivatives in all of them, nitrates in some, hydrogen peroxide in others with some overlap, and azides in a few. One had so much hydrazoic acid I’m a little surprised I’m not scattered around the cavern where I found it, so watch yourselves, all of you.”
Carol reacted gleefully. “The next step is to find how they make the compounds. The primary energy source practically has to be the sun, but…”
“It’s getting hotter as you go down,” Charley interjected. Carol was silenced for a moment.
Molly decided to play safe, and made the obvious answer. “Another point to check as we go. I wonder how hot it will really get. Even in this gravity, there must be a limit before the rock creeps and these caverns close.”
“Well, it’s a young planet, we’ve been assuming. Maybe the creeping is still going on.” Molly looked uneasily at the sections of cavern wall that her light and Carol’s allowed them to see.
“I’m not sure I really like that thought. If you must dwell on it in conversation, please stress the word creep. Anyway, we’ll look for more life, now that the liquid has changed to water. Things certainly ought to be different.”
“But it isn’t all water,” Carol reminded her. “Ammonia from above is still mixing with it—which I suppose contributes to some of the heating that’s been worrying us. The pure water has been vapor, condensing on cold walls.”
“Right. Right. But do you know any life forms that operate anywhere near fifty-fifty ammonia-water mix? All I’ve ever heard of are either one or the other, with the one not the main solvent usually quite poisonous in more than trace amounts. My own body produces ammonia, but I have a couple of very complex organs we call kidneys whose main job is to get rid of it and some chemical machinery to turn it into something less toxic until they do. There are plants, if they are plants, growing in that river, Carrie. Are they water-based with evolutionary provision to avoid the ammonia, like me, or the other way around, or what?”
“Collect them. We’ll see.” Carol actually examined her own carefully labeled cans, selected one, discarded its contents, and replaced it with material from the river. She re-sealed the cover and redid the label, looking almost defiantly at Molly with one eye as she did so.
The Human said nothing to the implied challenge, but after a moment remarked, “We’ll be back, you know.”
“I know. Specific answers are more interesting than general ones, though.” The giant had to agree, at least for the moment. They remounted the robot, and continued down river and through caves, sometimes more or less horizontally, quite often chasing another fall from top to bottom—much more cautiously now. They had less to go on but were inclined to agree with Joe’s estimate that a quarter to a third of Enigma’s volume was open. At the thought of the increasing thickness of planet above, Molly found herself less and less resentful of the negligible gravity. Maybe it was just as well that the rock didn’t weigh much.