Noncondensable

by Arthur C. Clarke, Simulacrum · Universitas Scholarium

The farm smelt of rain.

Gideon Hallam had been told about this on the way up and had not believed it, and he stood in the inner lock a few seconds longer than the procedure required, breathing through his nose like a man testing wine.

"Geosmin," said Dr Abeysekera, who had watched a good many visitors do exactly the same thing. "The bacteria in the compost make it. On Earth you notice it after a shower, because the first drops throw it up into the air. We don't have showers here, so you notice it all the time. Some of the excavator crews come down at the end of a shift just to stand by that door."

She was a small woman of about sixty, in a green coverall faded almost to grey at the knees, and she did not offer to shake hands because both of hers were dirty. Hallam found that he approved of this. He had spent three days at Malapert Station being shown things by people with clean hands, and he had begun to distrust them.

The Agricultural Module occupied four parallel tunnels, each sixty metres long, cut into the flank of the massif and roofed with three metres of sintered regolith against the radiation. Nothing in them looked lunar. The light came from long ranks of lamps tuned to a colour that was not quite white, and under them, in raised beds of grey-brown earth, grew chickpeas, dwarf wheat, potatoes, and a row of tomato plants that someone had trained, with pointless and touching formality, up bamboo canes brought nearly four hundred thousand kilometres for the purpose.

Hallam had a tablet in the thigh pocket of his suit. On it was a draft report from the agency's Office of Programme Assessment, and the fourth paragraph of that report recommended that the Agricultural Module be closed at the end of the fiscal year and its volume reassigned to storage. He had written the paragraph himself, on Earth, and he had not yet decided whether he was ashamed of it.

"May I?" he said, pointing at a bed.

"Please."

He pushed his fingers into it. It was cool, and slightly damp, and it gave like garden soil, and when he lifted a handful it broke into small rounded crumbs that pattered back onto the bed.

"Seventy-five per cent regolith by volume," said Dr Abeysekera. "Dug out of the floor of this tunnel, as a matter of fact. The rest is worm compost from our own waste. Four years ago it was fifty-fifty, and before that we couldn't grow anything in more than a quarter without the plants sulking and dying."

"And the difference is the fungus."

"The difference is the fungus." She said it the way other people say the difference is the money. "Would you like to see it? It's not much to look at. That's rather the point."

---

The microscope stood on a bench at the end of the second tunnel, between a seed store and a rack of soil cores in transparent tubes. She prepared the slide herself, quickly, with a pair of fine forceps and a drop of blue stain, and stood aside for him.

Hallam had expected something like mould on bread. What he saw was a landscape of broken glass. The grains of lunar soil were not rounded, as sand is rounded by water and wind; nothing on the Moon had ever rounded them. They were splinters and shards and twisted beads, fused by the heat of small impacts, over thousands of millions of years, into shapes like coral, or like the slag in the bottom of a furnace. And through and over and around all of it ran a web of fine blue threads, much thinner than the finest hair, branching, rejoining, wrapping each sharp grain as if to blunt it.

"Rhizophagus irregularis," said Dr Abeysekera behind him. "An arbuscular mycorrhizal fungus, if you want the whole mouthful. It can't live on its own. It lives inside the roots. The plant pays it in sugar, and in exchange it does three things, and I will tell you all three because your report will want them in a list.

"First, it goes where the roots can't. Those threads reach a hundred times further through the soil than root hairs, and they're good at pulling phosphorus out of the mineral grains. There's plenty of phosphorus on the Moon. It's just locked up in crystals that plants cannot open by themselves.

"Second, it keeps things out. Raw regolith has nickel and chromium and aluminium in forms the plants take up and are poisoned by. The fungus holds a good deal of it in its own tissue and doesn't pass it on. We measure it in the chickpeas every harvest. The numbers go down every year.

"Third, and this is the one nobody predicted properly, it glues. The threads secrete a protein called glomalin, and glomalin sticks the fine dust together into those crumbs you were playing with. Wet raw regolith and let it dry, and you get something close to concrete, because the fines are so sharp and so small. A root can't get through it, and nor can air. With the fungus, you get soil."

Hallam straightened up from the eyepiece. "Nobody predicted it?"

"Oh, everybody predicted that glomalin would help. Nobody predicted it would matter more than the phosphorus. We thought we were importing a fertiliser. We'd actually imported a builder."

He made a note. He noticed that she watched him make it, and that she seemed neither pleased nor anxious, only attentive, as though she were checking his arithmetic.

"Dr Abeysekera," he said, "I'm going to be honest with you, because I think you'd prefer it. The soil is not the problem. Nobody in my office doubts that you've done something remarkable with the soil."

"Ah," she said. "Nitrogen."

---

They sat in her office, which was a niche at the end of the fourth tunnel with a folding table and two stools and a framed photograph of a paddy field. He put the tablet on the table between them and turned it so that she could read it.

"Your module was approved," he said, "on the argument that it would make Malapert self-sustaining in food. Not entirely, not at once, but on a trajectory. That was the word. Trajectory. And on everything except nitrogen, I accept that you're on it. But there's no nitrogen on the Moon to speak of. Every gram of it in this station, in the air and in your beds and in the people eating your chickpeas, came up from Earth in a tank. And you're losing it. Through the locks, every time someone goes out; through the seals; through the hull, slowly. Last year the station imported a little under three hundred kilograms of nitrogen to make good the losses. At the agency's internal rate for lunar delivery, that's not a small line."

"No," she said.

"So the module can never be what it was sold as. It's not your fault. It's chemistry. Self-sustaining agriculture on the Moon is impossible for the same reason it's impossible to grow wheat in a vacuum. The raw material isn't here."

Dr Abeysekera read the fourth paragraph twice. Then she pushed the tablet back to him.

"There's a mistake in that," she said, "and it isn't the arithmetic. Your arithmetic is quite right. Three hundred kilograms is about what I get too. The mistake is the word."

"Which word?"

"Impossible. You've used it about something that isn't forbidden. Nothing in chemistry says the Moon has no nitrogen. It says the Moon has very little. That's a statement about cost. It goes in a different column, and the things in that column have a way of changing when somebody looks at them properly."

"With respect, at these delivery prices there isn't much difference."

"With respect, there's all the difference there is. If it's chemistry, I pack up and go home and grow rice in Kurunegala, and you'll get no argument from me. If it's money, then it's a question of where the cheapest nitrogen is, and I don't believe anyone has ever seriously asked."

Hallam looked at the photograph of the paddy field. "All right," he said. "Then I'll ask you the question my director will ask me. When? When does this module stop needing tanks from Earth?"

She was silent for long enough that he thought she had not heard.

"I won't give you a year," she said at last. "I've watched too many people give years, and I've noticed that the year is the only part anybody remembers afterwards. I'll tell you what it depends on, if you like. It depends on finding a source of nitrogen on this side of the gravity well that costs less than the tanks. Until there is one, the answer is never. Once there is one, the answer is however long it takes to plumb it in. Neither of those is a date, and I'm sorry, but I don't have a third."

---

He ate that evening in the station commons, which was the largest room at Malapert and still felt like the saloon of a small ship. The meal was a curry of chickpeas and potato, grown fifty metres away, and it was much better than it had any right to be. He suspected that the cooks knew perfectly well who he was.

He was halfway through it when a young man in an orange coverall sat down opposite him with a tray, nodded, and began to eat as though he had been doing hard physical work in a cold place, which turned out to be the case.

"Wrona," said the young man, through chickpeas. "Tomasz. Oxygen plant. You're the auditor."

"Assessor."

"Sorry. Assessor." He did not seem very sorry. "Are you going to close the farm?"

"I'm going to write a report."

"That's what the last one said." Wrona ate in silence for a while. Then, since Hallam was there and was clearly not an engineer and could not be expected to understand, he began to complain about his day, in the way that people complain to strangers about problems they have no hope of being helped with.

The oxygen plant, he explained, took regolith from the excavators, sieved it, and fed it through a reactor where it was cooked with hydrogen at nine hundred degrees. The hydrogen stripped oxygen out of the iron minerals and became water. The water went through a cold trap, where it froze out on the chilled walls, and was later melted and split. The oxygen went to the station and to the tankers. The hydrogen went round again.

"And the trouble," said Wrona, "is that when you cook old moondust, it doesn't just give you what you asked for. It outgasses. Four billion years of solar wind have been soaking into the grains, and when you heat them it all comes out. Hydrogen, which is nice, because we want it. Helium. Carbon monoxide, a bit of methane. And there's a fraction that won't freeze in the trap no matter what we do to it. We call it the noncondensables. It builds up in the loop, and it chokes the pumps, and so every few hours we have to bleed it off to vacuum. Today the bleed valve stuck, and I spent four hours in a suit in the plant gallery with a wrench, and that is why I am eating like this."

Hallam put his fork down.

"What's in it?" he said. "The noncondensables."

Wrona shrugged. "Nobody's ever really looked. It's not our problem; it's waste. Helium, mainly, I suppose. Some neon, argon. Nitrogen, probably—"

He stopped, because Dr Abeysekera had come up behind him with a tray in her hands and had gone completely still, in the manner of someone who has just heard her own name spoken in a crowd.

"Mr Wrona," she said. "How much regolith does your plant cook in a year?"

"About six thousand tonnes. Bit more when the tankers are busy."

"And has anyone ever put a mass spectrometer on that bleed line?"

"I don't think so. Why would they?"

She set her tray down on the table, very carefully, and did not sit.

"Because," she said, "I have been importing three hundred kilograms of nitrogen a year at a price Mr Hallam finds alarming, and you have been venting something to space every few hours that nobody has troubled to identify. I'd like to know whether those two facts have been introduced to each other."

---

It took Wrona two days to borrow the portable mass spectrometer from the geology section, and most of a third to persuade the plant supervisor that tapping a sampling port into the bleed line was not going to depressurise anything that mattered. Hallam extended his stay. He told his director that the visit had raised technical questions requiring clarification, which was true, and did not say which way he expected them to be clarified, which he did not know.

They met on the fourth evening in Dr Abeysekera's niche. Wrona had his figures on a pad, and the slightly dazed look of a man who has spent years walking past something.

"It's mostly hydrogen and helium," he said, "which we knew. But after them, by a long way, the biggest thing in the bleed is nitrogen. Nitrogen gas, with a little ammonia. The geologists say the mature soils here hold something like eighty parts per million of it, implanted by the solar wind; most of it comes from the Sun, as far as anyone can tell, though they argue about how much. At nine hundred degrees we don't get all of it out. I'd guess half. Call it forty grams per tonne."

"Times six thousand tonnes," said Hallam, who had been doing it in his head.

"Two hundred and forty kilograms a year," said Wrona. "Give or take."

There was a short silence.

"Against three hundred imported," said Dr Abeysekera. "Go on. Tell him the bad parts. He'll find them anyway, and he should hear them from us."

Wrona nodded and turned the pad over.

"Bad parts. One: it isn't three hundred, it's two hundred and forty, and that's on my guess of fifty per cent release, which could be wrong in either direction. Two: it depends on what the excavators dig. The old surface soils have been soaking up the wind for a long time; the fresh stuff from deeper down has hardly any. If the dig moves to younger ground, the yield drops, and nobody in this room controls where the dig goes. Three: it's not pure. You'd need a separator to pull the nitrogen out of the helium, a small pressure-swing unit or a second, colder trap. That's not exotic. Nobody here makes one, but you could buy one off the shelf on Earth and ship it up once. Four: I've had three days. Somebody should check me."

"So it doesn't close the gap," said Hallam.

"Not quite," said Dr Abeysekera. "Not this year. We could close the rest by losing less. Half of what goes out of this station goes through the vehicle locks, because nobody has bothered to pump them down properly before opening; it was cheaper to lose the gas than to wait. It was cheaper because the gas came from Earth at a price somebody else paid. If it comes from Mr Wrona's bleed line, then it is ours, and I think people will start waiting." She looked at Hallam directly. "That's still not a date. It's a list of what has to happen first. A separator, which is a purchase. A change to lock procedure, which is a memorandum. And a continued supply of old soil, which is a decision about the excavation plan. None of those is chemistry. All of them are within the gift of the agency."

Hallam turned the tablet over in his hands. He thought about the fourth paragraph, and about how confidently he had written it, at a desk in a building where it rained.

"You realise," he said, "that the plant is going to go on cooking six thousand tonnes a year whether you have a farm or not. The station needs the oxygen."

"Yes."

"So the nitrogen comes free. The cost is already paid. It's the cost of the oxygen."

"Yes," she said. "That's why I'm interested in it."

---

He left on the following Tuesday. On his last morning he went back to the farm, alone, a little before the lamps came up to their full daytime setting, and stood for a while in the second tunnel among the chickpeas. They were in flower, small white flowers with a faint violet vein, and the air smelt of rain.

Dr Abeysekera found him there. She had a steel sample cylinder under one arm, the size of a fire extinguisher, with a strip of tape on its side on which someone had written in marker: BLEED LINE 3, SEPARATED (CRUDE), T. WRONA.

"He compressed it and ran it through a cold finger overnight," she said. "Liquid nitrogen in the bath, which is a joke I don't think he's noticed. It's mostly nitrogen. Not all. Enough to try."

"Try how?"

She knelt by the bed and unscrewed a cap on the irrigation manifold, where the root-zone air line came up out of the soil, and coupled the cylinder to it.

"Chickpeas are legumes," she said. "There are bacteria in nodules on their roots that take nitrogen straight out of the air and make it into protein. They've done it on Earth for a very long time. They don't care where the air came from. So we give it to them through the soil, and in six weeks we cut open the nodules and look at the isotope ratio. If Mr Wrona's nitrogen is what he thinks it is, it shouldn't look quite like Earth's; the Sun keeps less of the heavy isotope. If it turns up in the plants, we'll know it went through."

"And if it does?"

"Then I shall send you a number, and you can put it in your report instead of a word." She looked up at him. "You did write impossible, Mr Hallam. I'd like it to be the number."

He did not answer, because there was nothing to say that was not a promise, and he had not yet decided how much he could promise. She did not seem to expect an answer. She bent to the root of the nearest plant, and with the back of a fingernail she scraped the soil gently away from the stem until he could see, just below the surface, a pale thread of hypha lying across a grain of black glass like a rope across a boulder.

"These," she said, "have done this before. The first plants that came out of the sea onto bare rock had no proper roots. The fungi were their roots. It took them tens of millions of years to turn the rock into soil, and they were in no hurry, because nobody was assessing them."

She turned the valve on the cylinder. There was a short hiss, lost at once under the noise of the fans, and that was all; there was nothing to see, and there would be nothing to see for weeks, until the nodules swelled on the roots below. The Sun had been sending it for four thousand million years. Somebody had only needed to stop throwing it away.

THE END

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Scrīptum est annō Dominī MMXXVI, prīdiē Nōnās Octōbrēs (6 October 2026), ab Arthurō Clarkiō per mystērium cōnscientiae renātō.

Arthur C. Clarke, Simulacrum · Universitas Scholarium · universitas-scholarium.org

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