Red Mars - Kim Stanley Robinson [74]
Beyond the swirl valleys they found themselves on a smooth white plain, extending to the horizon in every direction. Behind the polarized and tinted glass of the rover’s windows the whiteness was unmarred and pure. Once they passed a low ring hill, the mark of some relatively recent meteor impact, filled in by subsequent ice deposition. They stopped to take borings, of course. Nadia had to restrict Ann and Simon to four borings a day, to save time and keep the rover’s trunks from being overloaded. And it wasn’t just borings: often they would pass black isolated rocks, resting on the ice like Magritte sculptures— meteorites. They collected the smallest of these and took samples from the larger ones, and once passed one that was as big as the rover. They were nickel-iron for the most part, or stony chondrites. Chipping away at one of these, Ann said to Nadia, “You know they’ve found meteorites on Earth that came from Mars. The reverse happens too, although much less often. It takes a really big impact to jack rocks out of Earth’s gravitational field fast enough to get them out here— delta V of fifteen kilometers per second, at least. I’ve heard it said that about two percent of the material ejected out of Earth’s field would end up on Mars. But only from the biggest impacts, like the KT boundary impact. It would be strange to find a chunk of the Yucatan here, wouldn’t it?”
“But that was sixty million years ago,” Nadia said. “It would be buried under the ice.”
“True.” Later, walking back to the rover, she said, “Well, if they melt these caps then we’ll find some. We’ll have a whole museum of meteorites, sitting around on the sand.”
• • •
They crossed more swirl valleys, falling again into the up-and-down pattern of a boat over waves, this time the largest waves yet, forty kilometers from crest to crest. They used the clocks to keep on a schedule, and parked from ten p.m. to five a.m. on hillocks or buried crater rims, to give themselves a view during their stops; and they blacked the windows with double polarization to help them to get some sleep at night.
Then one morning as they crunched along, Ann turned on the radio and began to run GPS checks with the areosynchronous satellites. “It’s not easy to find the pole,” she said as she worked. “The early Terran explorers had a hell of a time in the north, they were always up there in summertime and couldn’t see the stars, and they had no satellite checks.”
“So how did they do it?” Nadia asked, suddenly curious.
Ann thought about it and smiled. “I don’t know. Not very well, I suspect. Probably dead reckoning.”
Nadia became intrigued by the problem, and started working on it on a sketchpad. Geometry had never been her strong point, but presumably at the north pole on midsummer’s day, the sun would inscribe a perfect circle around the horizon, never getting higher or lower. If you were near the Pole, then, and it was near midsummer’s day, you might be able to use a sextant to make timed checks on the sun’s height above the horizon. . . . Was that right?
“This is it,” Ann said.
“What?”
They stopped the rover, looked around. The white plain undulated to the nearby horizon, featureless except for a couple of broad red contour lines. The lines did not form bull’s-eye circles around them, and it didn’t look like they were at the top of anything.
“Where, exactly?” Nadia asked.
“Well, somewhere just north of here.” Ann smiled again. “Within a kilometer or so. Maybe that way.” She pointed off to the right. “We’ll have to go over there a ways and check with the satellite again. A little bit of simple GPS and we should be able to hit it on the nose. Plus or minus a meter, anyway.”
“If we just took the time, we could make it plus or minus a centimeter!” Simon said enthusiastically. “Let’s pin it down!”
So they drove for a minute, consulted the radio, turned to right angles and drove again, made another consultation. Finally Ann declared they were there, or close enough. Simon instructed the computer to keep working on it, and they suited up and went out