Greg Egan - Incandescence

He turned to Parantham. "Assuming there's someone in there, why can't the Aloof keep them safe? Do you think they could really have been unaware of this place until we came here?"

"We don't know that they're not looking after them," she countered. "Maybe they're tweaking all the local stellar orbits, even as we speak. Maybe they've wrapped their giant hands around this spark of life to shield it from harm, just as meticulously as they've shielded the bulge from intruders."

"Then why are we here? What do they expect us to do?"

Parantham shook her head. "I could spin some half-plausible theory about them hunting for companions for these lonely foundlings, but the truth is I really don't know. It's not our responsibility to read their minds, though; our responsibility is to whoever is inside that Ark."

"To do what , exactly?" Rakesh hadn't realized quite how tense he was until he heard it in his own voice. He didn't want the fate of a civilization resting on his shoulders, but nor could he simply turn and walk away. Any people who'd survived their world being dragged from star to star and then torn apart deserved sanctuary. What he did not want to do, though, was blunder in and destroy their paradise, if they had already found it right here.

Parantham said, "Whether the Aloof are pulling our strings, or whether they really don't give a damn what we do, in the end we only have our own judgment. All we can do is tread carefully. I say we wait a few weeks to see if anyone answers our message. If they don't, we go in as unobtrusively as possible and take a look around."

Standing on the surface of the Ark at the point closest to the neutron star, Rakesh could feel the plasma wind and the tidal gravity trying to peel him off and fling him away into the accretion disk. It was like hanging upside down in a stiff breeze, albeit in low gravity and very low pressure. The adhesive pads on his jelly-baby feet could easily resist his avatar's minuscule weight, but the insistent tug was still disconcerting. It was no wonder that in all of their time watching the Ark they had seen no locals foolish enough to venture outside.

Parantham said, "Come on, it's this way." He followed her across the gray plain; the surface felt rough to his clinging feet, but it was flat to the eye and bore no visible cratering. The plasma around them was extremely hot, but also very thin; its temperature in Kelvin made it sound like it would fry anything instantly, but if you calculated its energy density it suddenly seemed a whole lot tamer. The inner edge of the disk and the plasma falling on to the surface of the neutron star were emitting hard radiation that would not have been too healthy for an organic body, but it was nothing to their avatars, and the Arkrock would block it once they were inside.

The crack they'd found was even narrower than the last one, and they'd had to shrink their avatars accordingly. Parantham entered first and Rakesh followed, reaching up by bending sharply at the waist to get a handhold before unsticking his footpads. They could have used their ion thrusters and let the autopilots navigate them through the crack without even touching the sides, but to Rakesh that would have ruined the whole sense of presence; he might as well have sent in a surveyor probe and merely watched the feed from its cameras. Whatever the Arkdwellers might think, he felt far more comfortable making an uninvited entrance in this form than he would have about sending in an autonomous spying device; this way seemed respectful, rather than sneaky. No doubt that reflected his own cultural bias, but until he had something better to go on it was as good a basis for choosing his actions as any.

As soon as they reached a point sheltered from the direct force of the wind, fungus began appearing on the Arkrock. Rakesh took some samples and sequenced them; they were recognizable cousins of the species on the other Ark, though there were significant genetic differences relating to the different environments. As they clambered up the walls, the winding of the crack soon blocked out the starlight, but this time as well as the thermal radiation of the walls themselves they had another kind of light to see by: the Arkrock was translucent to a band of terahertz radiation being produced by electrons spiraling around the magnetic field lines of the plasma. This window appeared to have been tuned to the predominant frequency in the plasma surrounding the Ark's natural orbit, so it was almost certainly a deliberate part of the design. The Arkmakers had not built a dark world of subterranean tunnels and caverns; they had made a world of glass and set it swimming in a sea of light.

Combining the visual processing techniques they'd used in the previous Ark with sensitivity to this new illumination was remarkably effective; although the kind of information they were receiving was very different from that yielded by the usual scattering of light from surfaces, making use of the right cues still generated a rich, detailed sensorium. Rakesh found that he could distinguish most of the species of fungus by sight, and even spot one kind buried beneath another. It was a shock at first to realize that almost nothing was completely opaque across this new spectrum, but once you accepted that fact the potential confusion abated. It was still possible to determine which of two things in your line of sight was the closest; it was just a matter of abandoning the old expectation that the nearer would obscure the farther as a matter of course.

They passed through a point where the fungus was exuding tendrils that criss-crossed the width of the break in the wall. As Rakesh understood the organism's behavior from genome-based simulations, this structure would develop into a net that would trap drifting material — both the "sand" of eroded Arkrock and the mineral-rich corpses of micro-organisms — and use it to reconstruct the wall. Perhaps within a century or two the fissure would be completely sealed.

They emerged from the crack and clambered up on to the floor of a small tunnel; though it dwarfed their tiny avatars, it was less than a centimeter wide. Dozens of varieties of fungus were growing on the walls, inflecting the Arkrock's crystalline translucence with a rich spectrum of colors. If this place turned out to be empty of higher lifeforms, it would not be for want of food. Rakesh could feel the plasma wind even now, flowing right through the walls.

Parantham said, "We don't seem to have sprung any alarms yet, but I suspect they don't have a big problem with intruders."

"No."

"So what now?"

"We take it slowly," Rakesh suggested. "Give them a chance to react. Wait here a couple of hours, to avoid appearing hostile or impatient. If there's no response, we go a little deeper and do the same again."

They waited. Rakesh was sure that certain kinds of fifty-million-year-old civilizations could not have avoided noticing their presence the instant their feet touched the Ark, but then, they were also the kind most likely to have left this place behind completely. The various possibilities were not mutually exclusive, though: even a technologically advanced culture with the power to travel far from the Ark need not have deserted it, and the fact that he and Parantham were not yet facing a welcoming party was no proof that the Arkdwellers had died out or migrated elsewhere.

After two hours with no sign that they'd been noticed, they started walking along the tunnel.

As they approached an intersection the sensors in Rakesh's avatar began to pick up a faint, complicated set of vibrations coming through the rock. It didn't match the footfall of the twelve-legged creatures they'd found in the other Ark; if it was being caused by any kind of animal, it was a large group of a different species altogether.

At the intersection they turned into a wider tunnel, following the vibrations. Their own footsteps didn't seem to be attracting attention, but then even if they were audible in principle this crowd's own noise might have been drowning them out.