“IR sensitivity isn’t enough. We need to rewrite our whole visual processing system,” she suggested.
Rakesh searched the library. Leaving aside olfactory and tactile modes—sniffing or groping your way through the dark—most underground species employed vibration sensors or sonar. The walls here were excellent sound conductors, but even so that would be of limited use. He found a mode of IR-based perception that some asteroid-mining robots and a few tunnel-dwelling species relied upon. It involved extracting and interpreting very small temperature differences from thermal emissions; it was exactly what he and Parantham needed.
The tunnel snapped into focus, decorated with elaborate patterns where the fungus in all its variety grew. Despite the strangeness of the view, the new system felt right: Rakesh knew where he was now, how to move, and what to expect to see when he did. It was unsettling to be reminded that
They set out along the tunnel, which loomed over them like some monumental feat of engineering. It was only about two centimeters wide, but Rakesh had no way of knowing whether its builders would have viewed it as a cramped passageway, a great highway, or something in between.
They’d chosen not to use the avatars’ vibration sensors as their primary mode of perception, but that didn’t stop them picking up a faint but rising beat conducted through the tunnel wall. “Should we go and explore that?” Parantham asked.
Rakesh said, “It sounds as if it’s coming toward us already.”
A giant creature came scurrying around a bend in the tunnel. It was moving on twelve legs like a busy arthropod, about a millimeter across. Their mode of vision rendered it translucent, revealing hints of membranes and chambers flexing and contracting within.
When it changed course to charge straight toward them Rakesh suppressed the urge to flee; their avatars were extremely robust, and in any case easily replaced. The creature halted and inclined the axis of its body toward him; it seemed presumptuous to assume that it was lowering its face, when Rakesh could make no immediate sense of the complex mass of bristles, knobs and tendrils that confronted him. A cluster of these organs suddenly sprang forward and made contact with his avatar, wrapping it and holding it firmly; he steeled himself for the shock of being vicariously swallowed, but after a moment the creature unwrapped him and disengaged. It stood motionless for a second or two, as if pondering the need for another taste, then it turned away and continued down the tunnel, as rapidly as it had approached.
Parantham said, “We should follow it.”
“Yes.”
The avatars had small fusion-powered ion thrusters attached like backpacks; with no gravity or air resistance to overcome, catching up with the creature and flying a few centimeters above it was easy. Having dismissed them as inedible once, the creature seemed untroubled by their presence, if it was aware of them at all.
The creature had shed cells on Rakesh’s avatar, and he had the nanomachines sequence them as he flew. They shared the fungus’s vacuum-hardening traits, and a large proportion of its other genes, both natural and introduced.
Parantham said, “I’d like to run a morphogenetic model. What do you think?”
“Coarse-grain it, and I think that would be ethical.” Software could take the genome and use it to simulate a growing embryo. A fine-grained simulation would necessarily experience everything that a real organism would, but a coarse-grained simulation could provide information about the range of generic experiences that were possible, without anyone actually experiencing them.
“All right.”
In a spare corner of Parantham’s mind, a sketch of the virtual creature took shape. While Rakesh watched the adult below him scurrying along, pausing now and then to graze on patches of fungus, a second viewpoint showed him an annotated diagram of the developing embryo in its egg case. As morphogen gradients washed over the dividing cells, eight distinct segments formed, the middle six slowly sprouting a tightly folded pair of legs each. Mouthparts, excretory and reproductive organs were whittled out of the growing mass of cells. The developing nervous system was extremely simple, and by the time the egg hatched it was close to hardwired: a handful of innate drives and reflexes would enable this creature to move, feed and mate, but it had no potential to do anything more complex.
Like all DNA-based life it was Rakesh’s distant cousin, but it was unlikely to be a direct descendant of whoever had built this ark.
“It doesn’t use infrared at all,” Parantham observed. “It listens for sounds conducted through the tunnel wall.”
“So how did it home in on me when I was standing stock still?” Rakesh examined the model’s results more closely. “Aha. Resonances set up by its own footsteps. A kind of sonar, after all.” It was impossible to say exactly how this creature’s natural ancestors had lived, but the engineered traits it possessed were extensive and ingenious. The Arkmakers might not have had the technology to locate, let alone reach, another planet like their own, but they had worked hard to adapt life to their new environment.
“So where are its designers?” he asked Parantham.
“Be patient,” she replied. “We’ve barely scratched the surface.”
When they reached a fork in the tunnel, they launched a small probe to keep following the twelve-legged creature, and they took the other turn, in toward the center of the ark.
Rakesh kept waiting for a riot of new lifeforms to appear before his eyes—to cross some threshold that marked the end of the barren outskirts, and witness a sudden explosion of diversity—but all they saw were the same kinds of fungus and the same spider-like creatures eating it. In fact, the further they went the sparser the fungus became.
“The stellar wind powers the whole ecosystem,” Parantham mused. “But it barely penetrates this deep. Parts of the walls are permeable to it, parts are not; it’s as if they designed the ark to have a certain flow, a certain set of currents running through it. But the wind must have been much stronger then. These days, it’s too feeble to do the job. And there doesn’t seem to be any other mechanism for transporting energy in toward the center.”
Rakesh didn’t reply, but he couldn’t help following her argument to its logical conclusion. The Arkmakers had invented a whole new ecosystem to live in after the death of their planet, but the vagaries of the bulge had defeated them yet again. They had relied on the hot winds from nearby giant stars as their new primary energy source, turning their backs on the relatively weak radiation from their small but stable foster-sun. Giant stars had short lives, and while new ones were always being born, in any particular place the stellar wind could ebb and flow dramatically on a time scale of just a few million years. The Interloper might have finished off the Steelmakers, but it could have provided whoever came after them with more or less constant light for another three billion years.
As they flew deeper into the ark, the fungus disappeared completely. The interior was barren. With nothing to repair them, the walls became increasingly cracked; small thermal stresses over the millennia had torn at the structure, in places reducing it to loose piles of rubble. Electromagnetic probes revealed what might once have been a network of copper wires running through the walls—distributing power, perhaps, or information—but they were just fragmented segments now, worn and snapped by minuscule but relentlessly patient forces.
About halfway to the center, rubble blocked their way. They despatched a swarm of small probes that could squeeze into the interstices, then backtracked and took a turn sideways, to see if there was anything that they could explore “for themselves”. Rakesh had grown used to his new body, and he was reluctant to give it up and return his senses to
He said, “Fifty million years is a long time to expect anyone to stay cooped up in a place like this. Maybe the Arkmakers finally developed interstellar travel, mined the asteroids for some raw materials, and then headed right out of the NSD to search for a safer home.”
“That’s possible,” Parantham replied. “And if we can’t see the hole where they burrowed out of this cocoon, maybe the fungus sealed it off.” She hesitated. “The design still doesn’t make a lot of sense to me, though. Even if the stellar winds were much stronger when this place was built, I can’t see what the flow was optimized
