Hal Clement - Still River

“And why would it form primarily at the summer pole?” asked Jenny.

“I would suggest that Arc’s radiation is supplying the activation energy for the reaction. I don’t know how big that is, offhand, but carbon dioxide is stable enough so that a reasonably large kick must be needed.”

“I agree,” said the Rimmore at once. “I don’t have the actual value in my head, either, but your point is a good one.”

“All right, I see that, but where does the gas come from?” No one was surprised that the question came from Charley, but for once no one blamed him—not even Carol, who had been on the point of asking it herself.

“I can think of two possibilities,” Joe replied, much more slowly. “I’m afraid I don’t like either one very much, but—well, here they are. One is that Molly’s ice, which made the kames you folks are exploring, is still below in large quantities and is still boiling out of the planet.”

“And the other? " Carol thought she knew what was coming. She was right.

“The other is that your life forms are returning the gases to circulation, seasonally or constantly.”

“Then we were wrong to go upwind; there are no inbound currents anywhere on the planet!” exclaimed Molly.

“I wouldn’t say that. It’s a quantitative question. Huge masses of atmosphere travel from winter to summer hemisphere; it seems quite possible that some of it goes below the surface.”

“Of course! There must be inward currents at the winter pole!” cried Charley.

“You make my hearts leap out of time,” Carol said, in a tone that needed no translation. “There’s no ’must be’ about it!”

“If my numbers are right, so is Charley,” Joe’s went on calmly. Carol silently came over to Molly and began to help heat the robot.

Molly wondered whether she could blush under her fur.

Molly was uncomfortable. It was dark. She had not seen or talked to Rovor or Buzz for weeks, and she was lonely, fond as she was of Carol. She had eaten nothing but recycled synthetics for more days than she cared to count. She felt grimy and itchy, and knew that the latter sensation was not entirely subjective; she had not been out of her armor for a long, long time.

But she was happier than she had been for a while. The feeling that her own carelessness had interfered with everyone’s work, including her own, had gone; now there were useful, planned tasks for everyone that would not have existed without her mistake.

Joe’s air-circulation project had been expanded to include underground currents; it was now evident that these were a significant part of Enigma’s wind pattern. Joe was grateful for the discovery, and—surprisingly—visibly eager to set about the new work. Jenny and Carol were practically wallowing in the wealth of biological and biochemical information flooding in, or would be once they could collect and study it properly. Molly herself was still unsure about her ice hypothesis, since the likelihood of a spongy interior for Enigma was now pretty strong, but mineral analysis and dating as she had originally planned them were still very appropriate. She and Charley also had their activity lines clear, therefore.

The fact that she and Carol were still physically out of touch with the surface somehow was only an inconvenience now, rather than the major worry it had been. Inconveniences could be faced; they ended after a while. The whole School experience was an inconvenience of sorts; living in a dome on airless Pearl, with the endless, nagging fear that her child would make some mistake which his frequently nonhuman caretakers would fail to recognize in time and which could easily kill him was bad even for a stable, healthy Human. Though it had been generations since one of her species had been born or raised on Earth, most of them lived on colony worlds where one could at least stand the local environment for a few days rather than a few seconds. The School was worth it for her and Rovor; the present experience was probably going to be worth it for her; the upbringing would, beyond much doubt, be very good for little Buzz—in her saner moments Molly knew that he was not really in any great danger even when she and his father were parsecs away; but she was a normal parent, and the anxiety was there. She was glad—now that the immediate danger seemed to be moving toward resolution—she could relax a little.

Molly knew that this change in attitude had to be subjective, but she welcomed it anyway. Joe, now on his way to the winter pole with a third mapping robot to check on caves with inblowing winds, would expand the inside charting of the planet. The simple mathematical fact that the complete job should still take half a million years or so seemed less impressive than when the Kantrick had called attention to its magnitude. Somehow, Joe’s being directly involved seemed to make things different. Her own rescue and Carol’s, she now felt, would fit automatically into the new scheme of activities. Like the Shervah, she found herself paying nearly total attention to the research immediately before them.

With one exception. The robot was still powered down, and the hours of life remaining in their armor’s batteries were growing steadily fewer. Carol, exploring on foot for new organisms, had found a small tunnel from which a relatively warm wind seemed to be coming. She had been impressed enough by their situation to help drag the metal cylinder to its mouth, and even spent some time debating with the others the advisability of following this passage when—she did not say if —they resumed powered travel; but she seemed still unworried as ever.

Jenny had found a small river and was following it downward, occasionally supplying the encouraging report that it seemed to be getting larger. Charley was methodically, and for him, silently, expanding his diagram of Enigma’s interior downward and southward. At the moment the two were out of electromagnetic touch, and their mapping computers were working independently, but every few hours they found themselves close enough together so the machines could update each other’s records. There were a number a points of overlap and connection; while it would have taken some hours of backtracking at the moment, either could have rejoined the other without going all the way back to the surface.

The Nethneen’s voice broke a long silence. “You will be pleased to hear that 1 have so far located six caves of varying size. Four of them show no evidence of connection with any larger system, but two have strong inward flow of air.”

“Then the ice theory is out,” Molly replied promptly.

“It becomes very much less probable” was the cautious answer.

“Leaving biology as the surviving contender.” Jenny made no attempt to conceal her satisfaction.

“If you mean the idea that life forms are responsible for reversing the gas-to-solid reaction and returning ammonia and carbon dioxide to the atmosphere, there is a very serious flaw.” If Joe felt any pleasure at pointing this out, the fact was no more obvious than usual.

“What’s that?” asked Jenny.

“The reaction would have to take place underground, judging from the direction of gas flow. Where would your life forms get their energy? The overall process is endothermic, obviously. If it is going on, you people should be much closer to the site than I am. What are your local creatures doing?”

“I ... don’t know,” Jenny admitted. “I’ve found a lot of plantlike stuff along my route, but haven’t collected any of it because it seemed to me that the search for Carol and Molly had to come first. If I had picked anything up, I don’t suppose I’d be able to tell what it was doing chemically without getting it back to the lab.”