It was getting toward the end of the long northern spring, and they still had no good supply of water, so Ann proposed to make an expedition to the cap and set up a robot distillery, along the way establishing a route that rovers could follow on automatic pilot. “Come with us,” she said to Nadia. “You haven’t seen anything of the planet yet, just the stretch between here and Chernobyl, and that’s nothing. You missed Hebes and Ganges, and you’re not doing anything new here. Really, Nadia, I can’t believe what a grub you’ve been. I mean why did you come to Mars, after all?”

“Why?”

“Yes, why? I mean there’s two kinds of activities here, there’s the exploration of Mars and then there’s the life support for that exploration. And here you’ve been completely immersed in the life support, without paying the slightest attention to the reason we came in the first place!”

“Well, it’s what I like to do,” Nadia said uneasily.

“Fine, but try to keep some perspective on it! What the hell, you could have stayed back on Earth and been a plumber! You didn’t have to come all this way to drive a goddamn bulldozer! Just how long are you going to go on grubbing away here, installing toilets, programming tractors?”

“All right, all right,” Nadia said, thinking of Maya and all the rest. The square of vaults was almost finished, anyway. “I could use a vacation.”

They tookoff in three big long-range rovers: Nadia and five of the geologists, Ann, Simon Frazier, George Berkovic, Phyllis Boyle, and Edvard Perrin. George and Edvard were friends of Phyllis’s from their NASA days, and they supported her in advocating “applied geological studies,” meaning prospecting for rare metals; Simon on the other hand was a quiet ally of Ann’s, committed to pure research and a hands-off attitude. Nadia knew all this even though she had spent very little time alone with any of these people, except for Ann. But talk was talk; she could have named all the allegiances of everyone at base if she had to.

The expedition rovers were each composed of two four-wheeled modules, coupled by a flexible frame; they looked a bit like giant ants. They had been built by Rolls Royce and a multinational aerospace consortium, and had a beautiful sea green finish. The forward modules contained the living quarters and had tinted windows on all four sides; the aft modules contained the fuel tanks, and sported a number of black rotating solar panels. The eight wire mesh wheels were 2.5 meters high, and very broad.

As they headed north across Lunae Planum they marked their route with little green transponders, dropping one every few kilometers. They also cleared rocks from their path that might disable a robot-driven rover, using the snowplow attachment or the little crane at the front end of the first rover. So in effect they were building a road. But they seldom had to use the rockmoving equipment on Lunae; they drove northeast at nearly their full speed of thirty kilometers an hour, for several days straight. They were heading northeast, to avoid the canyon systems of Tempe and Mareotis, and this route took them down Lunae to the long slope of Chryse Planitia. Both these regions looked much like the land around their base camp, bumpy and strewn with small rocks; but because they were heading downhill they often had much longer views than they were used to. It was a new pleasure to Nadia, to drive on and on and see new countryside continually pop over the horizon: hillocks, dips, enormous isolated boulders, the occasional low round mesa that was the outside of a crater.

When they had descended to the lowlands of the northern hemisphere, they turned and drove straight north across the immense Acidalia Planitia, and again ran straight for several days. Their wheel tracks stretched behind them like the first cut of a lawnmover through grass, and the transponders gleamed bright and incongruous among the rocks. Phyllis, Edvard and George talked about making a few side trips, to investigate some indications seen in satellite photos that there were unusual mineral outcroppings near Perepelkin Crater. Ann reminded them irritably of their mission. It made Nadia sad to see that Ann was nearly as distant and tense out here as she was at back at base; whenever the rovers were stopped she was outside walking around alone, and she was withdrawn when they sat together in Rover One to eat dinner. Occasionally Nadia tried to draw her out: “Ann, how did all these rocks get scattered around like this?”

“Meteors.”

“But where are the craters?”

“Most are in the south.”

“But how did the rocks get here, then?”

“They flew. That’s why they’re so small. It’s only smaller rocks could be tossed so far.”

“But I thought you told me that these northern plains were relatively new, while the heavy cratering was relatively old.”

“That’s right. The rocks you see here come from late meteor action. The total accumulation of loose rock from meteor strikes is much greater than what we can see, that’s what gardened regolith is. And the regolith is a kilometer deep.”

“It’s hard to believe,” Nadia said. “I mean, that’s so many meteors.”

Ann nodded. “It’s billions of years. That’s the difference between here and Earth, the age of the land goes from millions of years to billions. It’s such a big difference it’s hard to imagine. But seeing stuff like this can help.”

Midway across Acidalia they began running into long, straight, steep-walled, flat-bottomed canyons. They looked, as George noted more than once, like the dry beds of the legendary canals. The geological name for them was fossae, and they came in clusters. Even the smallest of these canyons were impassable to rovers, and when they came on one they had to turn and run along its rim, until its floors rose or its walls drew together, and they could continue north over flat plain again.

The horizon ahead was sometimes twenty kilometers off, sometimes three. Craters became rare, and the ones they passed were surrounded by low mounds that rayed out from the rims: splosh craters, where meteors had landed in permafrost that had turned to hot mud in the impact. Nadia’s companions spent a day wandering eagerly over the splayed hills around one of these craters; the rounded slopes, Phyllis said, indicated ancient water as clearly as the grain in petrified wood indicated the original tree. By the way she spoke Nadia understood that this was another of her disagreements with Ann; Phyllis believed in the long wet past model, Ann in the short wet past. Or something like that. Science was many things, Nadia thought, including a weapon with which to hit other scientists.

Further north, around latitude 54°, they drove into the weird-looking land of thermokarsts, hummocky terrain spotted by a great number of steep-sided oval pits, called alases. These alases were a hundred times bigger than their terran analogues, most of them two or three kilometers across, and about sixty meters deep. A sure sign of permafrost, the geologists all agreed; seasonal freezing and thawing of the soil caused it to slump in this pattern. Pits this big indicated that water content in the soil must have been high, Phyllis said. Unless it was yet another manifestation of martian times scales, Ann replied. Slightly icy soil, slumping every so slightly, for eons.

Irritably Phyllis suggested that they try collecting water from the ground, and irritably Ann agreed. They found a smooth slope between depressions, and stopped to install a permafrost water collector. Nadia took charge of the operation with a feeling of relief; the trip’s lack of work had begun to get to her. It was a good day’s job: she dug a ten-meter long trench with the lead rover’s little backhoe; laid the lateral collector gallery, a perforated stainless steel pipe filled with gravel; checked the electric heating elements running in strips along the pipe and filters; then filled in the trench with the clay and rocks they had dug out earlier.