“No. We have to rule out high latitudes for the first mission.” Spacecraft arriving from Earth would naturally settle into a parking orbit around Mars with not much inclination to the equator; changing the orbit to reach the poles would take a lot of extra energy. “But it’s a shame; the poles are interesting.”

“What are the caps? Water ice?”

“Maybe. The orbit of Mars is more elliptical than Earth’s. And that distorts the seasons. In the south you get a short, hot summer, but a long, cool winter. And the makeup of the caps seems to differ as well. We think the cap in the north is water ice, yes. But the southern cap is probably carbon dioxide — dry ice.

“There are a lot of puzzles about the poles.” She walked across the room to a blowup photograph; it showed a thick band of layering in brownish terrain.

“What the hell’s that?” Bleeker asked. “It looks like melted chocolate.”

“These are bands of thick-layered deposits, thirty or forty feet thick, that surround the poles for hundreds of miles; they are made up of dust and ice, mixed up, laid down by the Martian winds. The bands tell us that the deposition process must vary, over the years. Or the millennia, anyhow. But what caused the variation? We’ve got three possible mechanisms. First, maybe the eccentricity of Mars’s orbit changes.”

“Why should it?” Stone asked.

“Mars is a lot closer to Jupiter than we are; Jupiter’s mass is capable of a lot of perturbation. Or maybe the tilt of the planet’s axis changes.”

“I can see how that would happen,” Stone said. “That bottom-heavy southern hemisphere would make a hell of a difference to Mars’s moment of inertia. The whole damn thing must wobble like a spinning top.”

She smiled. “On geological time scales, yes.”

“And what’s your third mechanism?”

“That the heat output of the sun changes, in some way we don’t understand.”

Bleeker frowned. “But that would change the Earth’s climate.”

“That’s right. And that’s why the layering is a good reason for going to the poles someday. Mars is like a dusty mirror, Phil, Adam; every time we look into it, we learn something about the Earth.”

They were silent for a moment, digesting that.

York felt pleased with herself. Even if they learned nothing else, if she could puncture their complacency, make them think about the significance of the flight they were likely to take, she’d have achieved something.

She glanced again at her polar blowup. It was actually of much lower quality than the images taken by later generations of probes, which had concentrated on equatorial landing-site mapping. Because of the Mars landing program, paradoxically, much less was known about the planet as a whole than might otherwise be possible.

And it was in the hands of guys like these to make it all worthwhile.