"Where are we going?" Madeline inquired. "You were running your sensors most of the night, right?"
A.J. sighed. "Much as I hate to admit it, I am at least partially defeated at the moment. You know how some of the weird alloys and composites the Bemmies had on Phobos kept messing with my sensors, from GPR on through just about everything else? Well, there's one big-ass chunk of this base that seems to be made out of that same stuff. I can't see anything past it—which means on the other side of the base, under it, and partly to the sides. And I can't drive Thoat around to check from different positions, obviously."
"So you got nothing?"
"I didn't say that. I just didn't get nearly as much as I hoped to get, and there's nothing that looks tremendously promising. We'll have to scout around the base perimeter—which is pretty darn big— for the next few days with portable units, if we want to get data on the rest of the area. I can say this much: if we're going to find entrances, that ridge"—he pointed to the fifty-meter-high cliff half a kilometer away—"is our best bet. Remember how we found the entrance to Phobos Base? Well, the same problem we faced on Phobos is here, only about a million times worse. Any opening that was standing on regular open ground will have filled in completely. I'm not sure if you can get solid rock out of just wind-blown stuff settling. But, if you can, after sixty-plus million years any openings that got filled in might be rock by now. Even if not, they'll have been completely buried eons ago. So, just like on Phobos, we have to look for caves or cracks that might have stayed open that long."
Helen nodded. "Makes sense. We do have one thing in our favor, too. Mars is geologically stable, compared to Earth. There's almost nowhere on Earth you could go which would have a chance of retaining any geological structures that old. Especially not things like caves and tunnels. But Mars has less gravity to collapse things, a lot fewer earthquakes, and—so far as we know, at least—no mechanism like plate tectonics to refurbish the surface every few hundred million years."
"Pretty much," Joe agreed, having been listening in. "It looks like it tried to go for that model around the time Olympus Mons got started. But without the ability to keep a liquid mantle, that was doomed to failure."
"The ridge it is, then." Madeline set off, the other two following. Close on A.J.'s heels came one of the two automated equipment and sensor rover carts they'd brought with them. Land-bound equivalents of the Faeries, essentially. It was loaded with portable GPS and other sensor equipment, plus rock-climbing gear.
"Back off a bit, Willis," he told it. Willis obediently fell back a meter or so farther, making A.J. feel less crowded.
Fifty meters was nothing compared to the main cliffs of Valles Marineris visible in the distance. But, up close, they were still formidable walls of red-gray stone, fissured and seamed, covered with the dust of years beyond count that sifted slowly down the rock face.
"Here's a hole big enough," A.J. said. He shone a light down. "Seems to go a fair distance, too."
After crawling into it for several meters, however, he learned the rough-floored tunnel narrowed to nothing. "Dry hole. Well, I didn't expect to find it right away."
"A.J., Madeline and I will keep looking for good possibilities in this rock face," Helen said. "You're wasting your skills doing that. Anyone can crawl into holes. See what you can get on GPR and your other gadgets."
"You got it."
A.J. began removing the equipment from Willis and setting it up. At least in this new location he'd have a different angle on the base and might get some shots at areas that had been completely obscured before.
Unfortunately, his repertoire was relatively limited here. The surface was heavily covered by drifting dust, so using acoustics would be basically useless. The Fairy Dust wouldn't help here, really. GPR and related RF approaches were pretty much all he could use without the ability to bore into bedrock. He could use a synthetic-aperture type approach to increase resolution and sensitivity, though, if he moved the GPR setup.
For the next several minutes he was busy reconfiguring Willis and setting the GPR unit firmly on the little rover. "There, that's got it. How are you people coming?"
"Lots of little holes and big holes," came Helen's slightly breathless voice. "But nothing promising, so far. You?"
"About to start getting us some more data." He started Willis and the GPR unit running. For the next hour he paced the sensor platform as it sent regular pulses into the Martian soil and bedrock, recorded the returns, and sent them to Thoat's main systems to analyze. He could, of course, have had Nike do the analysis—with the satellite network, they were never out of communication with the interplanetary vessel—but he liked doing things with what he had. And this analysis wasn't particularly difficult.