North of Galilaei it was easier. And then she was out of the slot, and onto Chryse Planitia. This was the heart of the trough, with a gravitational potential of -0.65; the lightest place on the planet, lighter even than Hellas and Isidis.

But one day she drove onto the top of a lone hill, and saw that there was an ice sea out in the middle of Chryse. A long glacier had run down from Simud Vallis and pooled in the Chryse low point, spreading until it became an ice sea, covering the land over the horizons to north, northeast, northwest. She drove slowly around its western shore, then its northern shore. It was some two hundred kilometers across.

Near the end of one day she stopped her car on a ghost crater rim, and stared out across the expanse of broken ice. There had been so many outbreaks in ‘61. It was clear that there had been some good areologists working for the rebels in those days, finding aquifers and setting off explosions or reactor meltdowns precisely where the hydrostatic pressures were the greatest. Using a lot of her own findings, it seemed.

But that was the past, banished now. All that was gone. Here and now, there was only this ice sea. The old seismographs she had picked up all had records disturbed by recent temblors from the north, where there should have been very little activity. Perhaps the melting of the northern polar cap was causing the lithosphere there to rebound upward, setting off lots of small marsquakes. But the temblors recorded by the seismographs were discrete short-period shocks, like explosions rather than marsquakes.-She had studied her car’s AI screen through many a long evening, mystified.

Every day she drove, then walked. She left the ice sea, and continued north onto Acidalia.

The great plains of the northern hemisphere were generally referred to as level, and they certainly were compared to the chaoses, or to the southern highlands. But still, they were not level like a playing field or a table top — not even close. There were undulations everywhere, a continuous up-and-downing of hummocks and hollows, ridges of cracking bedrock, hollows of fine drifts, great rumpled boulder fields, isolated tors and little sinkholes … It was unearthly. On Earth, soil would have filled the hollows, and wind and water and plant life would have worn down the bare hilltops, and then the whole thing would have been submerged or subducted or worn flat by ice sheets, or uplifted by tectonic action, everything torn away and rebuilt scores of times as the eons passed, and always flattened by weather and biota. But these ancient corrugated plains, their hollows banged out by meteor impact, had not changed for a billion years. And they were among the youngest surfaces on Mars.

It was a hard thing to drive across such lumpy terrain, and very easy to get lost when out walking, particularly if one’s car looked just like all the other boulders scattered about; particularly if one was distracted. More than once Ann had to find the car by radio signal rather than visual sighting, and sometimes she walked right up to it before recognizing it — and then would wake up, or come to, hands shaking in the aftershock of some forgotten reverie.

The best driving routes were along the low ridges and dikes of exposed bedrock. If these high basalt roads had connected one to the next, it would have been easy. But they commonly were broken by transverse faults, at first no more than line cracks, which then got deeper and wider as one progressed, in sequences like loaves of sliced bread tipping open, until the faults gaped and were filled with rubble and fines, and the dike became nothing but part of a boulder field again.

She continued north, onto Vastitas Borealis. Acidalia, Borealis: the old names were so strange. She was doing her best never to think, but during the long hours in the car it was sometimes impossible not to. At those times it was less dangerous to read than it was to try staying blank. So she would read randomly in her AI’s library. Often she ended up staring at areological maps, and one evening at sunset after such a session, she looked into this matter of Mars’s names.

It turned out most of them came from Giovanni Schiaparelli. On his telescope maps he had named over a hundred albedo features, most of which were just as illusory as his canali. But when the astronomers of the 1950s had regularized a map of the albedo features everyone could agree on — features that could be photographed — many of Schiaparelli’s names had been retained. It was a tribute to a certain power he had had, a power evocative if not consistent; he had been a classical scholar, and a student of biblical astronomy, and among his names there were Latin, Greek, biblical, and Homeric references, all mixed together. But he had had a good ear, somehow. One proof of his talent was the contrast between his maps and the competing Martian maps of the nineteenth century. A map by an Englishman named Proctor, for instance, had relied on the sketches of a Reverend William Dawes; and so on Proctor’s Mars, which had no recognizable relations even to the standard albedo features, there was a Dawes Continent, a Dawes Ocean, a Dawes Strait, a Dawes Sea, and a Dawes Forked Bay. Also an Airy Sea, a DeLaRue Ocean, and a Beer Sea. Admittedly this last was a tribute to a German named Beer, who had drawn a Mars map even worse than Proctor’s. Still, compared to them Schiaparelli had been a genius.

But not consistent. And there was something wrong in this melange of references, something dangerous. Mercury’s features were all named after great artists, Venus’s were named after famous women; they would drive or fly over those landscapes one day, and feel that they lived in coherent worlds. Only on Mars did they walk about in a horrendous mishmash of the dreams of the past, causing who knew what disastrous misapprehensions of the real terrain: the Lake of the Sun, the Plain of Gold, the Red Sea, Peacock Mountain, the Lake of the Phoenix, Cimmeria, Arcadia, the Gulf of Pearls, the Gordian Knot, Styx, Hades, Utopia…

On the dark dunes of Vastitas Borealis she began to run low on supplies. Her seismographs showed daily temblors to the east, and she drove toward them. On her walks outside she studied the garnet sand dunes, and their layering, which revealed the old climates like tree rings. But snow and high winds were tearing off the crests of the dunes. The westerlies could be extremely strong, enough to pick up sheets of large-grained sand and hurl them against her car. -The sand would always settle in dune formations, as a simple matter of physics, but the dunes would be picking up the pace of their slow march around the world, and the record they had made of earlier ages would be destroyed.

She forced that thought from her mind, and studied the phenomenon as if there were no new artificial forces disturbing it. She focused on her work as if clenching her geologist’s hammer, as if breaking apart rocks. The past was spalled away piece by piece. Leave it behind. She refused to think of it. But more than once she jerked out of sleep with the image of the long runout coming at her. And then she was awake for good, sweating and trembling, faced with the incandescent dawn, the sun blazing like a chunk of burning sulphur.

Coyote had given her a map of his caches in the north, and now she came to one buried in a cluster of house-sized boulders. She restocked, leaving a brief thank-you note. The last itinerary Coyote had given her said he was going to be dropping by this area sometime soon, but there was no sign of him, and no use waiting. She drove on.

She drove, she walked. But she couldn’t help it; the memory of the landslide haunted her. What bothered her was not that she had had a brush with death, which no doubt had happened many times before, mostly in ways she had not noticed. It was simply how arbitrary it had been. It had nothing to do with value or fitness; it was pure contingency. Punctuated equilibrium, without the equilibrium. Effects did not follow from causes, and one did not get one’s just desserts. She was the one who had spent too much time outdoors, after all, taking on far too much radiation; but it was Simon who had died. And she was the one who had fallen asleep at the wheel; but it was Frank who had died. It was simply a matter of chance, of accidental survival or erasure.