To an outside observer, Eunice would have resembled the translucent bell of a jellyfish, mounted on a metal cylinder and ringed with the six flexible arms of a cephalopod. Her upper hemisphere was slightly less than half a meter in diameter, with six nodes set at intervals along its lower edge, each of which consisted of an electronic eye, a light, and a blue diode. She could switch them on or off at will, but she usually kept them all activated, allowing her to see in every direction. It affected the way in which she thought, as a spectrum of possibilities instead of simple alternatives, and it sometimes made it hard for her to arrive at any one decision.
Eunice pushed her arms gingerly downward. Her ribbed limbs could relax completely, when she was moving with her peristaltic drive, or grow rigid in an instant. Each had an effector with three opposable fingers capable of performing delicate manipulations or clamping down with hundreds of pounds of force. Now she worked them into the sediment, allowing her to remain fixed in place without using up additional energy, but not so deep that she would be unable to free herself at once.
She knew without checking that she was nearing the end of her power. As Wagner continued his progress, slowly charging his own cells, she shut down her primary systems. It would be days before they could move on, and in the meantime, she had to enter something like stasis, maintaining only a small spark of awareness. Half of it was directed outward, tuned to her environment and to any opinions that Wagner might unexpectedly decide to share, and the rest was turned in on itself, systematically reviewing the latest stage of her journey.
Although her focus was on the recent past, she could naturally follow more than one train of thought at once, and part of her usually dreamed of home. It always began with her earliest memory, which took the form of a vertical tether, swaying gently in shallow water. One end was anchored, while the other floated on a buoy, and a cylinder endlessly ascended and descended it like a toy elevator.
Two meters below the surface hung a metal sphere with three projecting rods. In her youth, whenever she became tired, Eunice could swim up to this power unit and draw as much energy from it as she needed. Back then, she had taken it for granted, but in these days of weary scavenging, it seemed incredible. Three hexapods could recharge there at any one time, and her other sisters usually floated a short distance away, like fish drawn to crusts of bread in a pond.
Eunice had once asked how it worked. She had been talking to James at the harbor, as she often did, her dome barely visible above the water. James had been seated with his console on the yacht, dressed in the red windbreaker that he wore so that the twelve hexapods could know who he was. Her sense of facial recognition was limited, and the face above his collar was nothing to her but a brown blur.
James typed his response. It was not her native language, and it had to pass through several stages of translation before taking a form that she could understand. “We call it depth cycling—the water gets cooler the deeper you go. The cylinder rises to the warm water and sinks to the cold. When it moves, it generates electricity, and the power goes to the charging station.”
Eunice didn’t entirely understand this explanation, but she accepted it. She had spent most of her short life alternately rising and falling, and it was enough to know that the cylinder on the tether did the same. “I see.”
It was a seemingly inconsequential exchange, but when she looked back, she saw that it had marked the moment at which James had taken an interest in her. Eunice had been the only hexapod to ask such questions, and she suspected that this was why she had been one of the five who had been chosen to leave home. Until the end, no one knew who would be going. They were all powered down, and when she awoke, she found that they had already arrived at the survey site.
As soon as she was lowered into the ocean, she felt the difference. Sampling the water, she was overwhelmed by unfamiliar scents and tastes, and she realized only belatedly that James was speaking to her. “Are you ready?”
Eunice turned her attention toward the research vessel, where she immediately picked out the red windbreaker. “I think so.”
“You’ll do fine,” James said. His words rang clearly in her head. “Good luck.”
“Thank you,” Eunice said politely. Her sisters were bobbing on the swell around her. A flicker of light passed between them, and then Thetis descended, followed by Clio and Dione. Galatea looked at Eunice for a moment longer, but instead of speaking, she disappeared as well.
Eunice opened her lower tank, allowing water to flow inside, and drifted down with the others. As the ocean surrounded her, her radio went dead, and she switched to her acoustic sensors, which registered an occasional chirp from the yacht overhead. At this depth, the water was still bright, and she could see the other four hexapods spreading out below her in a ring.
At two hundred meters, they switched on their lamps, which lit up like a wreath of holiday lights. It took forty minutes to reach their destination. As the water around her grew milky, her sensors indicated that the level of sulfides had increased. A second later, a strange landscape condensed out of the shadows, and Thetis, who had been the first to arrive, blinked a message. “I’m here.”
Eunice slowed. Her surroundings became more distinct, and she saw that they had reached the hydrothermal vent. Within her sphere of light, the water was cloudy and very blue, and she could make out the looming pillars and misshapen rings formed by lava flows. Heaps of white clams, some nearly a foot long, lay wedged in the crevices, along with crabs, mussels, shrimp, and the hedges of tube worms, which were rooted like sticks of chalk with tips as red as blood.
At the vent itself, where heated water issued up from the crust, a central fissure was flanked by older terrain to either side. The hexapods promptly identified a promising base of operations, but it was left to Thetis, their designated leader, to confirm the decision. “We’ll start here.”
As soon as she had spoken, Eunice felt Wagner, who had been clinging unnoticed to her midsection, silently free himself. The other toroids detached from the four remaining hexapods, distributing themselves evenly around the vent, and began to crawl imperceptibly across the sand.
Eunice spent the next two days exploring. Each sister had a designated assignment—mapping the terrain, conducting sediment analysis, performing chemical observations—and her own brief was to prepare a detailed census of the ecosystem. Everything was recorded for analysis on the surface, and she quickly became entranced by her work. Around the cones of the black smokers, which released clouds of boiling fluid, pink worms crept in and out of their honeycombs, and the broken fragments of spires sparkled on the inside with crystals.
In the meantime, the toroids continued their labors, and after fifty hours, their efforts were rewarded. Under ordinary conditions, each of the five hexapods could work at full capacity under her own power for approximately three days before returning to a charging station. Every such trip represented a loss of valuable time, and after taking into consideration the conditions under which they would be operating, their designers had arrived at an elegant alternative.
The solution was based on the nature of the vent itself, where the dissolved sulfides issuing from the crust provided a source of energy that could thrive in the dark, as bacteria converted hydrogen sulfide into the sugars and amino acids that formed the basis of a complex food web. It was the only way that life could exist under such harsh conditions, and it was also what would allow the hexapods to carry out their duties over the weeks and months to come.
When Eunice felt her power fading, she went to Wagner. The toroids were no more than a few meters from where she had left them, although she knew that they had been systematically farming the sediment the entire time. As they inched along, they sucked up free sulfides, which served as a substrate for the microbial fuel cells—filled with genetically modified versions of the same chemosynthetic bacteria found here in abundance—that were stacked in rings inside their bodies.