Then one day the sky fell in earnest. The whole highest part of the water ice sheet cracked away from the CO2, collapsing through the mesh and into the lake and all over the beach and the surrounding dunes. Luckily it happened in the early morning when no one was down there, but in the village the first booms and cracks were explosively loud, and everyone rushed to their windows and saw most of the fall: the giant white sections of ice dropping like bombs or spinning down like skipped plates, and then the whole surface of the lake exploding and spilling out over the dunes. People came charging out of their rooms, and in the noise and panic Hiroko and Maya herded the kids into the school, which had a discrete air system. When a few minutes had passed and it appeared that the dome itself was going to hold, Peter and Michel and Nadia ran off through the debris, dodging and jumping over the shattered white plates, around the lake to the Rickover to make sure it was all right. If it weren’t it would be a deadly mission for the three of them, and mortal danger to everyone else. From the school window Nirgal could see the far shore of the lake, which was cluttered with icebergs. The air was aswirl with screaming gulls. The three figures twisted along the narrow high path just under the edge of the dome, and disappeared into the Rickover. Jackie chewed her knuckles in fear. Soon they phoned back a report: all was well. The ice over the reactor was supported by a particularly close-meshed framework, and it had held.
So they were safe, for the moment. But over the next couple of days, spent in the village in an unhappy state of tension, an investigation into the cause of the fall revealed that the whole mass of dry ice over them had sagged ever so slightly, cracking the layer of water ice and sending it down through the mesh. Sublimation on the surface of the cap was apparently speeding up to a remarkable degree.
During the next week the icebergs in the lake slowly melted, but the plates scattered over the dunes were still there, melting ever so slowly. The youngsters weren’t allowed on the beach any more: it wasn’t clear how stable the remainder of the ice layer was.
The tenth night after the collapse they had a village meeting in the dining hall, all two hundred of them. Nirgal looked around at them, at his little tribe; the sansei looked frightened, the nisei defiant, the issei stunned. The old ones had lived in Zygote for fourteen Martian years, and no doubt it was hard for them to remember any other life; impossible for the children, who had never known anything else.
It did not need saying that they would not surrender themselves to the surface world. And yet the dome was becoming untenable, and they were too large a group to impose themselves on any of the other hidden sanctuaries. Splitting up would solve that problem, but it wasn’t a happy solution.
It took an hour’s talk to lay all this out. “We could try Vishniac,” Michel said. “It’s big, and they’d welcome us.”
But it was the Bogdanovists’ home, not theirs. This was the message on the faces of the old ones. Suddenly it seemed to Nirgal that they were the most frightened of all.
He said, “You could move further back under the ice.”
Everyone stared at him.
“Melt a new dome, you mean,” Hiroko said.
Nirgal shrugged. Having said it, he realised he disliked the idea.
But Nadia said, “The cap is thicker back there. It will be a long time before it sublimes enough to trouble us. By that time everything will have changed.”
There was a silence, and then Hiroko said, “It’s a good idea. We can hold on here while a new dome is being melted, and move things over as space becomes available. It should only take a few months.”
“Shikata ga nai,” Maya said sardonically. Of course there were other choices. But she looked pleased at the prospect of a big new project, and so did Nadia. And the rest of them looked relieved that they had an option which kept them together, and hidden. The issei, Nirgal saw suddenly, were very frightened of exposure. He sat back, wondering at that, thinking of the open cities he had visited with Coyote.
They used steam hoses powered by the Rickover to melt another tunnel to the hangar, and then a long tunnel under the cap, until the ice above was three hundred metres deep. Back there they began subliming a new round domed cavern, and digging a shallow lakebed for a new lake. Most of the CO2 gas was captured, refrigerated to the outside temperature, and released; the rest was broken down into oxygen and carbon, and stored for use.
While the excavation went on they dug up the shallow runner roots of the big snow bamboos, and cantilevered them out of the ground and hauled them on their largest truck down the tunnel to the new cave, scraping leaves all the way. They disassembled the village’s buildings, and relocated them. The robot bulldozer and trucks ran all hours of the day and night, scooping up the battered sand of the old dunes and carting it back down into the new cave; there was too much biomass in it (including Simon) to leave behind. In essence they were taking everything inside the shell of Zygote dome along with them. When they were done, the old cave was nothing but an empty bubble at the bottom of the polar cap, sandy ice above, icy sand below, the air in it nothing but the ambient Martian atmosphere, 170 millibars of mostly CO2 gas, at 240° Kelvin. Thin poison.
One day Nirgal went back with Peter to take a look at the old place. It was shocking to see the only home he had ever had, reduced to such a shell—the ice all cracked above, the sand all torn up, the raw root holes of the village gaping like horrible wounds, the lakebed scraped clear even of its algae. It looked small and ramshackle, some desperate animal’s den. Moles in a hole, Coyote had said. Hiding from vultures. “Let’s get out of here,” Peter said sadly, and they walked together down the long bare poorly-lit tunnel to the new dome, stepping along the concrete road Nadia had built, now all ratcheted with treadmarks.
They laid out the new dome in a new pattern, with the village away from the tunnel lock, near an escape tunnel that ran far under the ice, to an exit in upper Chasma Australe. The greenhouses were set nearer the perimeter lights, and the dune crests were higher than before, and the weather equipment was set right next to the Rickover. There were any number of small improvements of that sort, which kept it from being a replica of their old home. And every day they were so busy with the work of constructing it that there was no time to think much about the change; morning classes in the schoolhouse had been cancelled since the fall, and now the kids were merely a rotating work crew, assigned to whoever needed help the most on that particular day. Sometimes the adult overseeing them would try to make their work into a lesson—Hiroko and Nadia were especially good at this—but they had little time to spare, and only added an explanatory sentence to instructions that were too simple to need explanation in any case: tightening wall modules with alien wrenches, carrying around planters and algae jars in the greenhouses, and so on. It was just work—they were part of the work force, which was too small for the task even so, despite the versatile robots that looked like rovers stripped of their exteriors. And running around, doing the work, Nirgal was for the most part happy.
But once as he left the schoolhouse and saw the dining hall, rather than the big shoots of Crèche Crescent, the sight brought him up short. His old familiar world was gone, gone forever. That was how time worked. It sent a pang through him that brought tears to his eyes, and he spent the rest of that day somewhat stunned and distant, as if always a step or two behind himself, watching everything that happened drained of emotion, detached as he had been after Simon’s death, exiled to the white world one step outside the green. There was nothing to indicate that he would ever come out of such a melancholy state, and how could he know if he ever would? All those days of his childhood were gone, along with Zygote itself, and they would never come back, and this day too would pass and disappear, this dome too slowly sublime away and crash in on itself. Nothing would last. So what was the point? For hours at a time this question plagued him, taking the taste and colour out of everything, and when Hiroko noticed how subdued he was, and asked him what was wrong, he simply asked her outright. There was that advantage to Hiroko; you could ask her anything, including the fundamental questions. “Why do we do all this, Hiroko? When it