But something in him made him keep trying. “Look, Ann, I’m an advocate of what people call the minimum viable model. It’s a model that calls for a breathable atmosphere only up to about the two- or three-kilometer contour. Above that the air would be kept too thin for humans, and there wouldn’t be much life of any kind— some high-altitude plants, and above that nothing, or nothing visible. The vertical relief on Mars is so extreme that there can be vast regions that will remain above the bulk of the atmosphere. It’s a plan that makes sense to me. It expresses a comprehensible set of values.”

She did not reply. It was distressing, it really was. Once, in an attempt to understand Ann, to be able to talk to her, he had done research in the philosophy of science. He had read a fair amount of material, concentrating particularly on the land ethic, and the fact-value interface. Alas, it had never proved to be of much help; in conversation with her, he had never seemed able to apply what he had learned in any useful manner. Now, looking down at her, feeling the ache in his joints, he recalled something that Kuhn had written about Priestley— that a scientist who continued to resist after his whole profession had been converted to a new paradigm might be perfectly logical and reasonable, but had ipso facto ceased to be a scientist. It seemed that something like this had happened to Ann, but what then was she now? A counterrevolutionary? A prophet?

She certainly looked like a prophet— harsh, gaunt, angry; unforgiving. She would never change, and she would never forgive him. And all that he would have liked to say to her, about Mars, about Gamete, about Peter— about Simon’s death, which seemed to haunt Ursula more than her . . . all that was impossible. This was why he had more than once resolved to give up talking to Ann: it was so frustrating never to get anywhere, to be faced with the dislike of someone he had known for over sixty years. He won every argument but never got anywhere. Some people were like that; but that didn’t make it any less distressing. In fact it was quite remarkable how much physiological discomfort could be generated by a merely emotional response.

• • •

Ann left with Desmond the next day. Soon after that Sax got a ride north with Peter, in one of the small stealthed planes that Peter used to fly all over Mars.