was almost sunset, the sky a great arch of violent colours, the sun low in the hazy west. The light would be behind her. She wound between dunes, then carefully made her way to the crest of one, and crawled the final metres of the way, and looked over the crest at the tower, now only a kilometre to the east. When she saw how close its base was she kept her chin right on the ground, among ejecta the size of her helmet.
It was some kind of mobile drilling operation, a big one. The massive base was flanked by giant caterpillar tracks, like those used to move the largest rockets around a spaceport. The drill tower rose out of this behemoth more than sixty metres, and the base and lower part of the tower clearly contained the technicians’ housing and equipment and supplies.
Beyond this thing, a short distance down a gentle slope to the north, was a sea of ice. Immediately north of the drill, the crests of the great barchan dunes still stuck out of the ice—first as a bumpy beach, then as hundreds of crescent islands. But a couple of kilometres out the dune crests disappeared, and it was ice only.
The ice was pure, clean—translucent purple under the sunset sky—clearer than any ice she had ever seen on the Martian surface, and smooth, not broken like all the glaciers. It was steaming faintly, the frost steam whipping east on the wind. And out on it, looking like ants, people in walkers and helmets were ice-skating.
It had come clear the moment she saw the ice. Long ago she herself had confirmed the big impact hypothesis, which accounted for the dichotomy between the hemispheres; the low smooth northern hemisphere was simply a superhuge impact basin, the result of a scarcely imaginable collision in the Noachian, between Mars and a planetesimal nearly as big as it. The rock of the impact body that had not vaporised had become part of Mars itself, and there were arguments in the literature that the irregular movements in the mantle which had caused the Tharsis bulge were late developments resulting from perturbations originating with the impact. To Ann that wasn’t likely, but what was clear was that the great crash had happened, wiping out the surface of the entire northern hemisphere, and lowering it by an average of four kilometres relative to the south. An astonishing hit, but that was the Noachian. An impact of similar magnitude had in all probability caused the birth of Luna out of Earth. In fact there were some anti-impact holdouts arguing that if Mars had been hit as hard, it should have had a moon as big.
But now, lying flat looking at the giant drilling rig, the point was that the northern hemisphere was even lower than it first appeared, for its bedrock was amazingly deep, as much as five kilometres beneath the dunes. The impact had blown that deep, and then the depression had mostly refilled, with a mixture of ejecta from the big impact, windblown sand and fines, later impact material, erosional material sliding down the slope of the Great Escarpment, and water. Yes, water, finding the lowest point as it always did; the water in the annual frost hood, and the ancient aquifer outbreaks, and the outgassing from the blistered bedrock, and the lensing from the polar cap, had all eventually migrated to this deep zone, and combined to form a truly enormous underground reservoir, an ice and liquid pool that extended in a band all the way around the planet, underlying almost everything north of 60°north latitude, except, ironically, for a bedrock island on which the polar cap itself stood.
Ann had discovered this underground sea many years before, and by her estimates between sixty and seventy percent of all the water on Mars was down there. It was, in fact, the Oceanus Borealis that some terraformers talked about—but buried, deeply buried, and mostly frozen, and mixed with regolith and dense fines; a permafrost ocean, with some liquid down on the deepest bedrock. All locked down there for good, or so she had thought, because no matter how much heat the terraformers applied to the planet’s surface, the permafrost ocean would not thaw any faster than a metre per millennium—and even when it did melt it would remain underground, simply as a matter of gravity.
Thus the drilling rig before her. They were mining the water. Mining the liquid aquifers direct, and also melting the permafrost with explosives, probably nuclear explosives, and then collecting the melt and pumping it onto the surface. The weight of the overlying regolith would help push the water up through pipes. The weight of water on the surface would help push up more. If there were very many drilling rigs like this one, they could put a tremendous amount on the surface. Eventually they would have a shallow sea. An ice sea to start with, but between atmospheric warming, sunlight, bacterial action, increased winds—it would melt eventually. And then there would be an Oceanus Borealis. And the old Vastitas Borealis, with its world-wrapping garnet barchan dunes, would be sea bottom. Drowned.
She walked back to her car in the twilight, moving clumsily. It was difficult to operate the locks, to get her helmet off. Inside she sat before the microwave without moving for more than an hour, images flitting through her mind. Ants burning under a magnifying glass, an anthill drowned behind a mud dam … She had thought that nothing could reach her any more in this preposthumous existence she was living—but her hands trembled, and she could not face the rice and salmon cooling in the microwave. Her stomach was a small stone in her body. In the random flux of universal contingency, nothing mattered; and yet, and yet …
She drove away. She couldn’t think of anything else to do. She returned south, driving up the low slopes, past Chryse and its little ice sea. It would be a bay of the larger ocean, eventually. She focused on her work, or tried. She fought to see nothing but rock, to think like a stone.
One day she drove over a plain of small black boulders. The plain was smoother than usual, the horizon its usual five kilometres away, familiar from Underhill and all the rest of the lowlands. A little world, and completely filled with small black boulders, like fossil balls from various sports, only all black, and all faceted to one extent or another. They were ventifacts.
She got out of the car to walk around and look. The rocks drew her on. She walked a long way west.
A front of low clouds rolled over the horizon, and she could feel the wind pushing at her in gusts. In the premature dark of the suddenly stormy afternoon, the boulder field took on a weird beauty; she stood in a slab of dim air, rushing between two planes of lumpy blackness.
The boulders were basalt rocks, which had been scoured by the winds on one exposed surface, until that surface had been scraped flat. Perhaps a million years for that first scraping. And then the underlying clays had been blown away, or a rare marsquake had shaken the region, and the rock had shifted to a new position, exposing a different surface. And the process had begun again. A new facet would be slowly scraped flat by the ceaseless brushing of micron-sized abrasives, until once again the rock’s equilibrium changed, or another rock bumped it, or something else shifted it from its position. And then it would start again. Every boulder in that field, shifting every million years or so, and then lying still under the wind for day after day, year after year. So that there were einkanters with single facets, and dreikanters with three facets—fierkanters, funfkanters—all the way up to nearly perfect hexahedrons, octahedrons, dodecahedrons. Ventifacts. Ann hefted one after another of them, thinking about how many years their planed sides represented, wondering whether her mind might not reveal similar scourings, big sections worn flat by time.
It began to snow. First swirling flakes, then big soft blobs, pouring down on the wind. It was relatively warm out, and the snow was slushy, then sleety, then an ugly mix of hail and wet snow, all falling down in a hard wind. As the storm progressed, the snow became very dirty; apparently it had been pushed up and down in the atmosphere for a long time, collecting fines and dust and smoke particulates, and crystallising more moisture and then flying up on another updraught in the thunderhead to do it again, until what came down was nearly black. Black snow. And then it was a kind of frozen mud that was falling, filling in the holes and gaps between the ventifacts, coating their tops, then dropping off their sides, as the keening wind caused a million little avalanches. Ann staggered aimlessly, pointlessly, until she twisted an ankle and stopped, her breath racking in and out of her, a rock clutched in each cold gloved hand. She understood that the long runout was still running. And mud snow pelted down out of the black air, burying the plain.
