BOUNDARY(149)

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.



"That isn't very promising," she remarked, as it clearly took them away from the base.



"Don't start complaining yet," A.J. said. "I'm still picking up water concentration."



"Full stop!" Madeline said from just ahead. Cautiously, they moved up at her signal to take a look.



The tunnel seemed to end here, until they got close and saw that what happened was that the tunnel itself had been essentially beheaded. A short bit of it remained ahead of them, while at their feet a wide crack dropped vertically into the depths. It was two meters across and much longer than that. From their current vantage point, they couldn't tell how much longer.



Madeline shone her light down the crack. There seemed to be a floor, over a hundred meters down. "Good enough, I think. Helen?"



The paleontologist agreed. "Yes, we'll make the descent. One at a time. I think you should go first, A. J., then me. Madeline, you bring up the rear since I think you're our best climber in case something goes wrong." She cocked her head. "Am I right?"



"Probably. I spent some time on the Matterhorn, once."



Seeing Helen's eyes roll in her helmet, Madeline protested: "Hey, it was just for the fun of it! I was on vacation, and I rather enjoy danger sports."