"It's not my fault," Madeline said, smiling that million-dollar smile. "He insisted I wake him up before we left. I felt bad about it, since I didn't let him sleep much in the first place. Broken leg be damned, he got no mercy from me last night."
Okay, then. Not delicate ground.
Putting on his helmet, A.J. glanced over at Joe in admiration. One of the things he'd always liked the most about his friend was his very solid ego. It just didn't seem to faze Joe at all that he'd gotten himself a woman who could probably outdo him in almost anything except engineering and cooking—and maybe not the cooking. At this point, A.J. wouldn't really be surprised to discover that Madeline Fathom was a Cordon Bleu graduate, on top of everything else. She seemed to pull out new skills the way a magician pulled rabbits out of a hat.
"A.J.?"
He suddenly became aware that Helen was speaking to him. "Huh?"
"I said, are you ready? What's up?"
"Just thinking, taking up too many processing cycles to detect your inquiry. Sorry, yes, I'm set. Got it all ready."
The three of them stepped into Thoat's airlock and cycled out onto the Martian soil. A.J. took a deep breath, as though he were stepping outside a mountain cabin and breathing in the air. The magnificent view called for some such gesture.
The orbital pictures had shown the area of Target 37 as being near, or even right below, a whitish chevron-shaped marking next to a small gully or canyon on the floor of the Melas Chasma area. Such images are deceptive, however. A.J. was struck again by just how deceptive they were as he glanced to his right.
There, about a quarter of a kilometer distant, was the edge of the so-called gully.
The term was a little ridiculous, he thought. The sheer scale of Valles Marineris warranted calling it a gully, perhaps, but on Earth it would be a canyon in its own right. More than three kilometers across at its widest, it ran a curved, slightly zigzag course for more than thirty klicks before petering out. Even here, where it narrowed drastically, it was several hundred meters wide and hundreds deep, red-pink-gray rock walls plunging down into a shadowed crease in the immensity of Mariner's Valley.
As they had been the first humans to reach the gully, they felt they had the right to name it. And since they'd done so through the services of the huge rover, they'd unanimously decided to name it "Thoat Canyon." Barring any official objections later, of course; but, under the circumstances, that was hardly likely.
The lighter soil, not so clearly whitish up close, had strong concentrations of salts in it. For reasons that were unclear to A.J., that news had been very exciting to the areologists on Nike and presumably on Earth. Small rises and cliffs surrounded the area to the north, where A.J. was facing, and to the left. Thoat had needed to round the southern part of its eponymous canyon and drive northwest to reach their current position, and he could see their tracks still visible in the sands to the south. The wind would undoubtedly erase them eventually, but for the moment he suspected that most of their course across Mars could be traced from orbit with a good enough telescope.
"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.
It was, however, increasingly disappointing. The more the returns came in and were processed, the more clearly the base on this side was delineated. And the less and less likely it became that there were, or e
ver had been, any entrances—natural or Bemmius-made—in this area.
Finally he shook his head. "Ladies, give it up. There's nothing to find here."
"Damn," said Madeline without rancor. "I was hoping we could find something fairly quickly—because I certainly don't like the idea of trying to dig our way down to the thing. Well, we still have more perimeter to check. Maybe tomorrow."
She started making her way down the backside of the ridge, which sloped much less steeply on that side.
It wasn't until a few moments later that it registered on A.J. that Helen hadn't responded. For a moment he almost panicked, until he saw that she was at the top of the ridge, looking outward. Maybe just admiring the view. It'd be a while—a long while—before any of them started taking that view for granted. Compared to Valles Marineris, the Grand Canyon in Arizona was a ditch.
"Helen, you okay?"
"Hmmm?" Her voice sounded distracted. He could almost see her expression; it was the one she wore when she almost had a problem solved. "A.J., what do your GPR scans say about the geology?"
"Geology? Well, I'm not an expert, but basically, um, we've got the top layer of crap, something that I guess might be sorta-sandstone under the dust and debris, then a bunch of denser stone, and something else under that. The sorta-sandstone isn't very thick, the denser stone is thicker—maybe fifty to a hundred meters total in this area, though I get vague indications it tends to be even thicker off to the west. The denser stone makes it real hard to see through past that, and I have to be honest that I wasn't using stuff that would look down past twenty to fifty meters anyway. Any tunnels we're looking for have to come nearer the surface than that. Why?"
She turned and gazed off towards the west, then back to the east. "Where were the close orbital photos of this area?" A moment later: "Yes, those are the ones. Thanks."
For a few more minutes there was silence. Then she said briskly, "We're looking in the wrong area. We want the east side."
"Over at Thoat Canyon, you mean?"
"Exactly. But it's not a canyon."
"Huh? Then what is it?"
Helen's voice was growing more excited and animated as she worked her way back down to his level. "I think it's the biggest damn sinkhole I've ever seen in my life. Look at the pictures again."
A.J. called up the images. The gash in the Martian landscape, now that he studied it more carefully, did have the folded, crumpled look of something that had collapsed from below. "But aren't most sinkholes round?"
"Generally, yes, but there are reasons it might not be. The way things sit in this region, and the shape of that collapsed area . . . What I think we have here is a collapse of a cavern which had a thin roof of volcanic basalt over it. The basalt is thicker in this area, but thinned drastically over there. That was at the edge of the flow, or some area that for some reason didn't get covered as well."
"A cavern . . . thirty kilometers long?"
"A network of them, maybe. Plus the gravity's so much less. Damn, I wish Ryu were still here. He'd know."
"Well, we can bounce this up to Nike and see what the experts have to say."
It wasn't long before Chad Baird, one of the planetographers, was on the radio with them.
"Quite possible. What you may have there is an area that used to have fossil ice in it. The ice slowly—over a period of millions of years—sublimed away and percolated through the rock above. It would refreeze in the upper layers, weakening them, then evaporate away again when things warmed up. Eventually there would be a huge empty space and weakened rock to give way during one of the infrequent major Martian quakes."
"And if the cap stayed intact here, and was thicker . . . Is it possible there could be some ice left under this area?"
"There could be, Helen, yes. With a large deposit underground, and a relatively impermeable basalt cap on top . . . Yes, there could be."
A.J. saw where this was going. "Good call, Helen. That's real good."
"You get it, then? Our best chance for any entrance is obviously on the wall of Thoat Canyon near the base, and the base is here almost certainly because somewhere down here they found water— which they needed even more than we do."
"Joe was right, then," A.J. mused. "It was no coincidence at all that Pirate wound up so close. That's one of the things we in Ares were looking for, too—water. And we decided to look here because Valles Marineris gets you deeper into the surface of Mars than anywhere else on the planet."
He was getting excited, now. "And if there is such an opening, I might be able to find it the same way we found the one on Phobos."
"Exactly. If there's any connection to fossil ice, any opening will show a higher water concentration."
A.J. found himself grinning in anticipation. "Let me get back to Thoat and do some work. We just might find our way in after all!"
Chapter 47
Helen's heart pounded as she was slowly lowered down the side of the three-hundred-meter cliff. "How much farther?"
"About fifty meters," A.J. answered. "Don't worry, I'm already here. Me and Madeline will pull you in."
Her hunch had been right. A.J.'s sensors, concentrated in the area along the rim of Thoat Canyon for several hundred yards, had in a day or so pinpointed three sources of excess water vapor, one of them clearly larger than the others. Lowering Willis via Thoat's winch, A.J. had found an opening nearly three meters high and almost that wide.
Although well-suited for open ground exploration, Willis was not designed for a spelunking expedition. There was no way around it but that they would have to take the risks themselves.
The fact that it was her idea and that she was the closest thing they had left to a geologist did little to comfort Helen on the way down. A three-hundred-meter drop would be fatal even in Mars' thirty-eight percent gravity. It was possible her suit might save her from instant death, but that sudden stop at the bottom would almost certainly leave her in critical condition—and with no medical facilities around to speak of, that would be even worse than immediate death.
However, she made it without incident. The other two pulled her inside and tied off the cable to a rock a few feet into the cave. It was with considerable relief that she felt her boots once more on solid stone. "All right, let's see what we have."
"Let's get these spare oxygen tanks set up first," A.J. said. "If an emergency comes and we wind up needing them, we don't want to be fumbling around."
That took only a minute. "Okay. Helen, I think you and Madeline should lead the way. I'll be leaving a trail of bread crumbs."
A.J.'s "bread crumbs" were small sensor and radio relays, which would permit them to continue to talk to the others even if they got quite a ways underground. That was necessary, if for no other reason than that Ken Hathaway had invoked his captain's authority and flatly forbidden them to go underground unless they could maintain communications.
It was a good idea anyway, leaving communications aside. Helen had some experience with exploring caves, and it turned out Madeline had even more. (For the usual non-reason: Spent five weeks, once, with a group of fanatic spelunkers. No, don't ask why. It's still classified.) Both of them knew how easy it was to get disoriented underground, with no lights beyond what they brought with them. But if they did get lost, A.J.'s bread crumbs would guide them out.
The tall opening in reddish-black stone slanted sharply downwards after the first few meters. It did not change much in size for quite a while, however, as the little party continued following it. After about sixty meters, the tunnel mostly leveled out and continued deeper into the cliff, towards the base.
"Dropping first relay," A.J. stated.
The walls of the tunnel were rough, showing no sign of intelligent shaping that Helen could detect. That didn't necessarily mean anything, of course. It did a dogleg to the left and then curved towards the southeast.