Interesting also in her own right, as it turned out when Maya met her in the Odessa offices a few days before their trip. With her great size (over two meters tall, and yet very rounded and muscular) and her fluid grace, and her high-cheekboned Asiatic features, she seemed a member of a new race, there to keep Maya company in this new corner of the world.

It turned out that Diana was completely obsessed with the Hellas Basin and its hidden water, and she talked about it for hours, at such length and in such detail that Maya became convinced that the mystery of parentage was solved — such a marsmaniac must be related to Ann Clayborne, and so it followed that Paul had been fathered by Peter. Maya sat in the train seat beside the big young woman, watching her or looking out the window at the steep northern slope of the basin, asking questions, observing as Diana shifted her knees against the seat back in front of her. They did not make train seats big enough for the natives.

One thing that fascinated Diana was that the Hellas Basin had proved to be ringed by much more underground water than had been predicted by the areological models. This discovery, made in the field over the last decade, had inspired the current Hellas project, turning the hypothetical sea from a nice idea into a tangible possibility. It had also forced the areologists to reconsider their theoretical models of early Martian history, and caused people to start looking around the rims of the other big impact basins on the planet; reconnaissance expeditions were under way in the Chari-tum and Nereidum Monies encircling Argyre, and in ihe hills ringing south Isidis.

Around Hellas itself they were near to completing the inventory, and they had found perhaps thirty million cubic meters all told, though some dowsers argued they were by no means finished. “Is there a way to know when they’re finished?” Maya asked Diana, thinking about all the requests for resources flooding her office.

Diana shrugged. “After a while you’ve just looked everywhere.”

“What about the basin floor itself? Might the flooding be destroying our ability to get to some aquifers out there?”

“No.” Almost no water, she told Maya, was located under the basin floor itself. The floor had been desiccated by the original impact, and now it consisted of about a kilometer’s depth of eolian sediment, underlain by a hard cake of brecciated rock, formed during the brief but stupendous pressures of the impact. These same pressures had also caused deep fracturing all around the rim of the basin, and it was this fracturing that had allowed unusually large amounts of outgassing from the interior of the planet. Vola-tiles from below had seeped up and cooled, and the water portion of the volatiles had pooled in liquid aquifers, and in many zones of highly saturated permafrost.

“Quite an impact,” Maya observed.

“It was big all right.” As a general rule, Diana said, impactors were about one-tenth the size of the crater or basin they made (like historical figures, Maya thought); so the impacting planetesimal in this case had been a body about two hundred kilometers in diameter, coming down on ancient cratered highland terrain. Signature traces of it indicated it had probably been an ordinary asteroid, carbonaceous chondrite for the most part, with lots of water and some nickel-iron in it. It had had a speed on arrival of about 72,000 kilometers per hour, and had hit at a slightly eastward angle, which explained the huge devastated region east of Hellas, as well as the high, relatively well-organized concentric ridges of the Hellespontus Monies to the west.

Then Diana described another rule of thumb which caused Maya to free-associate analogies to human history: the bigger an impactor, the less of it survived the impact. Thus almost every bit of this one had vaporized in the cataclysmic strike — though there was a small gravitational bolide under Gledhill Crater, which some areologists claimed was almost certainly the buried remainder of the planetesimal, perhaps one ten-thousandth of the original or less, which they claimed would supply all the iron and nickel that they would ever need if they cared to go digging for it.

“Is that feasible?” Maya asked.

“Not really. Cheaper just to mine the asteroids.”

Which they were doing, Maya thought darkly. That was what a prison sentence meant now, under the latest UNTA regime — years in the asteroid belt, operating the very strictly circumscribed mining ships and robots. Efficient, the Transitional Authority said. Prisons that were both remote and profitable.

But Diana was still thinking about the basin’s awesome birth. The impact had occurred about three and a half billion years before the present, when the planet’s lithosphere had been thinner, and its interior hotter. Energies released by the -impact were hard to imagine: the total energy created by humanity through all history was as nothing to it. And so the resulting volcanic activity had been considerable. Surrounding Hellas were a number of ancient volcanoes, which just postdated the impact, including Australis Tho-lus to the southwest, Amphitrites Patera to the south, and Hadriaca Patera and Tyrrhene Patera to the northeast. All of these volcanic regions had been found to have liquid water aquifers near them.

Two of these aquifers had burst onto the surface in ancient times, leaving on the eastern slope of the basin two characteristic sinuous water-carved valleys: Dao Vallis, originating on the corrugated slopes of Hadriaca Patera; and farther south, a linked pair of valleys known as the Harmakhis-Reull system, which extended for a full thousand kilometers. The aquifers at the heads of these valleys had refilled over the eons since their outbreaks, and now big construction crews had tented Dao and were working on Harmakhis-Reull, and were letting the water from the aquifers run down the long enclosed canyons, to outlets on the basin floor. Maya was extremely interested in these big new additions to the habitable surface, and Diana, who knew them well, was going to take her to visit some friends in Dao.

Their train glided along the northern rim of Hellas for all the first day, with the ice in view on the basin floor almost continually. They passed a little hillside town called Sebastopol, its stone walls Florentine yellow in the afternoon, and after that came to Hell’s Gate, the town at the bottom end of Dao Vallis. They walked out of the Hell’s Gate train station late in the afternoon, and looked down into a big ‘new tent town, located under an enormous suspension bridge. The bridge supported the train piste, spanning Dao Vallis just up from the canyon’s mouth, so that its towers were over ten kilometers apart. From the canyon rim by the bridge, where the train station was, they could see down the widening mouth of the canyon onto the basin floor, stretching out under a lattice of kinky sun-stained clouds. In the other direction there was a view well up into the steep narrow world of the canyon proper. As they walked down a staired and switchbacked street into the town, the new tenting over the canyon was visible only as a certain red haze to the color of the evening sky, the result of a dusting of fines on the tenting materials. “We’ll go upstream tomorrow by way of the rim road,” Diana said, “and get an overview. Then come back down on the canyon floor, so you can see what it’s like down there.”

They descended the street, which had 700 numbered steps. In Hell’s Gate’s downtown they walked around and had dinner, and then climbed back up to the Deep Waters office, which was on the valley wall just under the bridge. They stayed in rooms there, and next morning went to a garage by the train station and borrowed a small company rover.

Diana took the wheel and drove them northeast, paralleling the canyon rim on a road that ran next to the massive concrete foundation for the canyon’s tenting. Even though the fabrics were diaphanous to the point of vanishing, the sheer size of the roof made it a heavy weight to anchor. The concrete bulk of the foundation blocked their view down into the canyon itself, so that when they came to the first overlook, Maya had not seen into it since Hell’s Gate. Diana drove into a little parking lot up on the broad foundation itself, and they parked and put on helmets and got out of the car, and walked up a wooden staircase that seemed to ascend freestanding into the sky, although a closer look revealed first the clear aerogel beam supporting the staircase, and then the layers of tenting, stretching away from their beam to others that could not be seen. At the top of the stairs was a small railed viewing platform, with a prospect that gave a view of the canyon for many kilometers both upstream and downstream.