第1章 The Sounder

Delyth Amaral had spent four hundred and twelve days on Mars, and she could still tell when the ground was lying to her. The sled told her first. It was a flat aluminum plate on four low-pressure tires, towing the radar antenna behind it on a stiff bar, and every change in the regolith under the wheels came up through her hands. Hardpan rattled like a table being tapped. Dry sand in old fractures gave a long shushing noise. Buried ice was nearly silent, and that silence was the thing she had taught herself to distrust and to want in the same breath. She walked beside the sled because walking kept her warm and because the headset worked better at a walking pace than in a rover seat. Behind her, the antenna threw radio pulses into the ground. The echoes came back to a console strapped against her chest and built themselves into a picture of everything the surface was trying to keep. Anseris Basin lay behind her to the north, its domes the color of dried clay, its landing pad a scar of fused rock that caught the low sun and threw it back. Ten thousand people lived under those domes. Every one of them drank water that had been ice two days earlier, pulled out of ground just like the ground she was walking on. That was the whole of her job, when you stripped the paperwork off it: find the ice, measure the ice, tell the colony how long the ice would last. The public story of Anseris was clean and it fit on a recruiting poster. Aphelion Dynamics had come to Mars to make air. The Highline Program drilled shallow holes across the basin, warmed the ice they found, and let it sublimate up into the thin sky, adding water vapor and a little carbon dioxide a hectare at a time, year by year, working toward a thicker sky their grandchildren might breathe. Delyth had been hired to map the resource that made it possible. She believed in the arithmetic of it. She had never stopped believing in the arithmetic. She had only begun, slowly, to wonder who was doing the summing. Anseris ran on water the way a body runs on blood, and the colony had exactly one reservoir that mattered: a wedge of buried ice beneath the eastern flats, frozen into the regolith in layers like pages pressed together. The colonists called it the vault. The engineers called it K. Delyth called it, in her reports, the primary aquifer, because a report was not a place for affection, and she had grown a little affection for it anyway, the way a person grows fond of anything she has measured until she could find it by touch. She could tell you, without looking at a screen, how deep the ice lay under any dome in the basin, how old it was, how much of it the colony drank in a year, and how many years the arithmetic gave them before the vault ran thin. The number had been comfortable when she arrived. It had been comfortable for eleven months. In the last month, in the margins of her own spreadsheets, it had begun, very quietly, to move. "Line four, come back," said a voice in her ear. Sabra Oyelowo, drill foreman, three kilometers east and up to her elbows in the day's core. "Go ahead, Sabra." "You're drifting south of the grid again." "I am drifting exactly where the ice is." "That's what I said." A pause, and the click of a tool set down. "How far down is it today?" Delyth watched the radargrams crawl across her console, the bright bands stacking like rungs. "Reflector at one point nine meters. Ice lens, probably two meters thick, sitting on basalt. Nice and shallow. The model has it at four meters and patchy. The model is wrong again." "The model is always wrong again. That's why they pay you instead of a spreadsheet." "They pay me a salary and they pay the spreadsheet nothing. That's the difference." Sabra laughed, short and dry. "Get your line drawn. Dust is coming up on the western ridge and I don't want to drive out and fetch you." Delyth marked the run and kept walking. The sun was low and small, a white coin in a pink sky, and it threw her shadow far out ahead of her, long and thin like a wire touching the horizon. She had grown up on the coast of a wet country, and she still measured this light against that one, even after a year. Here the light did not warm. It only showed you things, hard-edged and exact, and it never pretended to be more than it was. She had come to Mars for the arithmetic and stayed for the ground. On Earth she had spent six years mapping aquifers that other people were busy draining, and she had watched the numbers fall while the meetings went on being polite, and she had decided, at thirty-four, that she would rather work somewhere the ground was honest. Mars was honest. Mars was cold and dry and utterly without pity, and it had never once in its long history pretended to be anything else, and Delyth found a kind of company in that. The company she worked for was a different matter, and the difference had begun to keep her up at night. At the fourth pass she stopped the sled and crouched over the console, frowning at a shape in the data that had no business being there. The reflector she had been tracking ended, as it should. Beneath it the radargram went quiet, that dark band that meant dense rock, the floor of the shallow aquifer. And below the floor, forty meters down, there was another return. Faint. Broad. A curve like a shallow bowl opening upward, the kind of echo that meant a boundary between rock and empty space. She had been mapping this sector for two seasons. There was no void here. The Long Survey, the original geology the colony had flown down with, said the basin floor was thick basalt clear down to the mantle. No caves. No lava tubes. Nothing that could trap a radio echo and hold it. She ran the pass again. The echo came back in the same place, patient and unmoved. Delyth sat down on the cold plate of the sled and let the wind push at her back while she stared at the screen. There were dull explanations available. A fault in the antenna. A processing artifact, a ghost of the shallow reflector folded into the deep record by the migration software. She had seen a hundred ghosts in a hundred radargrams and learned to dismiss them. This one did not have the loose, wandering look of a ghost. It had edges. "Sabra," she said. "When was the last time anyone drilled below thirty meters in this basin?" "Never, that I know of." A beat. "Why?" "No reason. Curious." "You are never curious with no reason. I've known you two years and you have never once been curious with no reason." Delyth looked at the bowl-shaped echo, and the echo looked back at her, flat and indifferent, daring her to write it down. She wrote the pass number, the coordinates, the depth, and beside them, in her own hand on the paper pad she still kept, four words no one had asked her for: possible void, forty meters. "Just a ghost," she said into the headset. "I'll chase it tomorrow." "Chase it tonight," Sabra said. "Tonight is when the model lets you. Tomorrow the paperwork starts." The wind picked up, dragging a low haze of dust across the western ridge, and the sun slid lower until the whole basin was the color of rusted iron. Delyth folded the pad into her pocket, unstrapped the console, and towed the sled home through the failing light, walking the way she always walked, eyes down, reading the ground for the next thing it might decide to tell her. Behind her, in the console's memory, the echo stayed where it was, waiting to be believed. ---