"Local concentration of sulfur where you are," she said.
There was a pause. "Don't see anything," said Mike.
"The bottom is quite rough below you," said Kassner. "We're getting a lot of scattering."
"I'll want to go down there," said Anna, and then grabbed hard for a wall rung when the floor beneath her began shaking violently. She hung on grimly as the shaking went on for several seconds. It stopped as quickly as it had begun.
"That was no gas bubble," said Anna. Kassner turned to look at her, and she didn't like what she saw in his eyes.
"Quake," said Kassner. "There were a few of them when Herschel was first inserted into the vent, but this is the first big one since. Hope it didn't plug up the vent. Mike, are you there?"
"Loud and clear," said Mike. "We just had some turbulence here, and something dark dropped past us toward the bottom."
"We had a quake up here, pretty strong, a shaker. You'd better come up right away."
"Okay. We've gone through our list for now; the rest has to be done at depth. That must have been a rock that came past us. It went down like a chunk of iron. Good thing it didn't hit us."
"I'll feel better when you see the vent is clear," said Kassner.
"Blowing tanks," said Phil. "We'll be there in a minute or two."
Anna was worried, and Kassner saw it on her face. "Good communications, so the shaft can't be plugged."
As if in reply, Mike called in only seconds later, "We have a little problem here," and at that instant Anna felt the floor shake again beneath her feet.
"Some debris on the shelf here, and another rock just came down. Wouldn't take much to make a tight fit. We'll clean it off with the articulators. Stand by."
The news was worse a minute later.
"Now we have a real problem. The port articulator is frozen up, and the servo is showing an overload when I try to deploy it. Starboard claw is working fine, and we're cleaning off the shelf, but we need to have both articulators working at depth. This could be a major repair."
"We don't have the time," said Anna.
"We'll make the time," said Phil. "I'm not taking this thing down with a broken arm and then take the blame if we need it."
"Understood," said Kassner. "For now, let's play it by ear."
"And I'm going down on the next dive," added Anna.
Phil started to say something, but there was a click and his voice was cut off.
Ten minutes later the vessel surfaced in a roil of bubbles and the hatch popped open. Phil climbed out and went straight to the port articulator folded tightly against yellow metal like an injured arm. "I need a speed wrench," he said, and a tech brought one to him.
Mike climbed out of the vessel, stepped over to the edge of the tank, and whispered to Kassner and Anna. "Let's get some coffee and let Phil work."
They went up one level and had coffee. "Dark down there, and clear," said Mike. "Any light color on the bottom would have shown up in our beams. There's rock peeking through ice on the walls, and especially on the ceiling. It was like a cave dive."
"Anything interesting will likely be on the bottom," said Anna. "The spectrometer showed some interesting sulfur spikes while you were down there."
"Oh," said Mike, "yes, there was one place where Phil thought he saw a couple of bubbles go by us."
Anna's heart leapt. "Did you record it?"
Mike shook his head. "Nope. It was just a few seconds after we came out of our dive."
"I'll backtrack it," said Anna. She turned to go back to lower level, and nearly ran into Phil as he came out of the central shaft connecting all levels. He looked both saddened and subdued.
"Well, I really screwed up."
"What?" Anna didn't know Phil was capable of admitting an error to anyone, let alone her.
"I should have inspected the articulators before we left Titan Base. A joint seal was split; God knows how long that bearing was exposed to hard vacuum. It looks like a porcupine."
Anna's mouth hung open in confusion.
"Epitaxial growth in hard vacuum has made hair crystals at the carbon boundaries and welded the joint. I don't suppose we have a high-voltage unit here; something at, say, thirty kilovolts and a milliamp?"
"Nothing like that," said Kassner.
Phil sighed, obviously upset with himself. Anna was strangely tempted to touch his arm in comfort.
"One quick check on Titan Station, and I would have found it. I can't burn it off, so I'll have to do it the hard way. I can snap the bearing out easy enough, but then I have to polish everything down to the original tolerances, and that's a trial-and-error hand job that could take days."
"We don't have days!" shouted Anna.
Phil winced, and Anna looked down at her feet.
"Sorry. We don't have time for blame, either. We only have ten Earth days at most. I'm willing to go down there with one articulator working."
"I don't think so," said Kassner, and Mike nodded in agreement.
"I need at least two dives to see what's down there," pleaded Anna. "In case you've forgotten, that is our primary mission."
"With help I can fix it in a day, two days tops," said Phil. "We'll work around the clock."
Everyone looked at Kassner, and he looked back at each of them in turn.
"I'm not hearing objections. Okay, recruit whoever you need, and do it."
"I'll help," said Anna.
Phil actually smiled at her. "No offense, but I'll use the techs. They know their way around a machine shop, and this is precision handwork we have to do. Thanks."
"Then I can use the time to go over the sonar scans and target some areas to look at. I'll have a plan ready for us in a day. Don't beat yourself up, Phil. We'll get this done," said Anna.
Phil couldn't look at her, simply mumbled something, turned, and climbed back down the central shaft to bottom level, where his work awaited him.
Mike put a hand on Anna's shoulder. "He's basically a good guy, you know. Right now his self-confidence is bruised, and we need to hope it heals fast."
"It has to," said Anna, but she worried about it. This is my last chance, she thought.
Her relief came a day and a half later, when Phil announced the articulator was now working, and Anna had to rush to finish her plan for the next dive.
There was another quake just before they submerged. Sonar showed no blockage in the vent below them, but a few small cracks had become big ones. The quakes were becoming more frequent. Kassner said it was a cyclic thing related to the positions of Titan and Mimas, and he expected the shaking to lessen soon.
Anna felt cramped in the submersible, was seated on a shelf behind Mike and Phil where she could watch the instruments and look out both the portholes and nose bubble at the same time.
Phil blew tanks gradually to slow their decent in a low-gravity environment where pumps and water-jets were a substitute for buoyancy. Using the bow planes, Phil literally flew the vessel down the vent and out over the shelf into deep water. He made a few swoops and turns, deployed both articulators, tested each joint before turning his attention to a map of areas Anna had found interesting. Anna leaned over his shoulder and pointed at the map as Phil and Mike studied it.
"The rough areas on the bottom are most interesting. There's a lot of sonar scattering in these three regions, and lighter detail in some others. I'd like to hit these five if we can, and while we're at it we can look closer at the smoother regions."
"We'll have to get around enough to map the entire cavern, and that's one dive by itself," said Mike. "It's in the mission statement, Anna."
"We can extrapolate a lot if we stay close to the bottom in the 30 percent we've already scanned." Anna pointed. "Go here first. You were above this area when I got a nice sulfur spike on the spectrometer."
"Okay," said Phil. Map coordinates were relative to the pinging buoy in the vent below Herschel, and they were already close. Phil began a slow descent on a helical path towards the bottom.
&nb
sp; Anna squinted, willing herself to see through the gloom. Her heartbeat quickened as Mike called off the distance to the bottom. At fifty meters they passed a bubble the size of a dinner plate. The view below was a dirty gray, and at twenty meters there was a dark splotch that moved across their view as Phil leveled out the dive and slowed.
At ten meters the bottom finally came into view, and at first Anna only felt disappointment. It looked like dark gray sand with occasional boulders protruding, nothing like what she'd expected from the sonar reflections.
But at three meters, Phil brought the vessel to a crawl, and the view outside was dramatically different. The boulders were now little towers of dark material like basalt, and the sand was a coarse gravel of dark rock and dirty ice. Even closer, the meter-high towers were made of dirty ice covered with an orange stain that reflected weakly in the bright lights. "We have to get a sample of that," said Anna.
Kassner had been watching everything from Herschel Base, and suddenly called in. "We're getting spikes for sulfur and sodium, and a trace of iron. The area you're in right now is loaded with methane, and it's over two-seven-seven Kelvin there. There was a sharp increase in temperature when you reached ten meters above bottom."
"Reminds me of Earth-side smokers, but there's all kinds of complex life forms around those things," said Anna. "All I see here is some kind of stain. We're sampling it. Could be bacterial."
"Wishful thinking," said Phil. "Looks mineral to me."
Phil looked surprised when Anna said, "You're probably right, but let's get a good sample of it, and also the gravel and bottom ice. That has a different sheen to it."
"Bubbles," said Mike, pointing.
Anna looked, and saw a stream of small bubbles leaking from the base of a tower, rising slowly and coalescing to form a single larger bubble, which drifted lazily upwards. "Can we get a temperature reading on that tower's surface?"
"Should have it," said Phil. He'd been working an articulator to break off a small nubbin from the side of the tower, and was dropping it into the specimen basket beneath the nose bubble.
"Two-eight-three Kelvin," said Kassner
"The bottom must be porous," said Anna. "These towers could be crystallites of a rock-ice mix where heat channels are coming through. I bet we have a mix of rock and methane clathrate down here, but if there are any methane breathers I sure don't see them."
Phil steered the submersible at a crawl through a small forest of towers, and columns of small bubbles rose from a few of them, but there was no sign of a living thing or any remnants of life, and then the bottom was soon relatively smooth again. They stopped for samples several times, but spent most of the dive just in sight of the bottom. They mapped the extent of the cavern in all directions. It was not so much an underground sea as it was a lake, unstable at best with all the seismic activity, and unlikely to be large or stable enough for life to have evolved there. There were more forests of little, bubbling towers, and vast expanses of black rock mixed with methane in ice, and by the end of the dive they had explored all the prime interesting areas Anna had marked on the sonar maps. There was a secondary list of prospects where small echo dispersions had been observed, but both Mike and Phil felt they had "seen it all" when they returned to Herschel Base. They left Anna to analyze the specimens they'd brought up and to define targets for the next dive. They would also be mapping the cavern ceiling in a search for other vents, and that was scheduled to take much of the dive time.
Anna expected her specimen analysis to take days, and there would only be time for one more dive before she had to leave.
Kassner seemed to sense her dark mood, and shared a cup of coffee with her that first evening back from the depths.
"You're disappointed," he said.
"I guess, but I have to admit a moon this small probably hasn't been around long enough in a tidal environment to evolve any life forms. It was a long shot, and a negative result is still a result. That's science."
"Would have been nice for the family history," said Kassner.
"You have a file on me?"
"You bet I do. Your pedigree is what brought you here."
"You must mean my grandmother. Do you know the Martian bacteria she discovered are still controversial? Half the science community still thinks it was a contaminant. And mom had to return to Earth before they even got a fourth of the way through Europa's ice. New discoveries are wonderful, but circumstances and a lot of luck are involved. And I have one more dive to get some."
"Then let's drink to luck," said Kassner, and he raised his squeeze bottle.
Their bottles touched as another small quake made the floor shudder beneath their feet.
Midway through the dive Anna felt herself relaxed but saddened, resigned to the fact the mission would be a scientifically interesting mapping of a subterranean lake beneath the surface of Enceladus. The geologists would be excited, but for Anna's colleagues in astrobiology there would be nothing to talk about. Her work on Titan had reached a dead end; the big moon had fascinating chemistry and geology, but no life. Perhaps she could return to Mars and build on what her grandmother had done. The gravity there was much higher, and she could then return to Earth in her later years and write up her lifetime of experiences in the outer regions of the Solar System. It would also tie together the work of three generations of women in her family.
For Anna, it was a good plan, and an acceptable plan, though her dream of finding extraterrestrial life was fading fast.
But it was a plan that changed abruptly after the fourth hour of the dive.
Sample analysis had shown no life. There was silicate rock mixed with dense, rich methane clathrate, and the stain on the little towers was iron sulfide. The gas bubbles were likely hydrogen sulfide, though she'd not been able to sample them directly. Every test for bacteria, every test for chemical reactions used by known life forms, had been negative.
For nearly four hours they had cruised near the bottom, observing occasional clusters of crystalline towers, but mostly vast plains of pebbles and methane-rich water ice. Kassner had called in twice with news of renewed quake activity, and they had seen several large chunks of ice drifting downward toward the bottom. Communication with Kassner had become garbled, cutting in and out after that. Mike was worried about it, and said so. "We might have to cut it short, Anna. With all these quakes, we don't want to be trapped down here."
Anna ignored his concerns. She had marked four places on the sonar maps where there were small depressions in the bottom that showed weak dispersions similar to what was seen with tower clusters. They were now nearing the first of them. Anna's attention had wandered a bit as she thought about returning to Mars, but something suddenly caught her eye.
"I see flashing lights," she said, and leaned forward to look ahead through the nose bubble. "Reflections?"
"No," said Phil. "I see it, too. Yellowishgreen—flickering, straight ahead."
"And beyond," said Mike. "One source is close, the other fainter."
In the darkness beneath the ice of Enceladus, the flashes of light suddenly ceased.
Phil had slowed to a crawl, but remained on course. The plain ahead was level, then rose a meter to form a hillock that curved away from them. And just beyond it was what Anna first thought was another tower, different this time, a feature glowing bronze in the bright lights of the submersible.
They came close, hovering over a crater-like depression two meters deep. The object it held reminded Anna of a dead tree with several bare branches. It was anchored in methaneclathrate and stood four meters high, and around it were several others only a meter tall. Branches swayed slowly in the turbulence created by the submersible's jets. Their surfaces were rough and mottled in bronze and dark brown, and from the dark areas streams of tiny bubbles pulsed in bursts that floated lazily upwards.
"Oh, my God, oh my God," gasped Anna, and she could scarcely breathe.
"It's soft," said Mike. "Hollow, maybe."
"Not rigid," whis
pered Anna. "Look at the tangle of tubules at its base, anchoring it to the ice. The bubbles have to be hydrogen. It's using methane. I think it's alive."
"A plant? Looks like a metal sculpture. Now it's not moving," said Mike.
"The jets are off. No more wake. The currents move it. That doesn't mean it's alive," said Phil, "but something was flashing lights at us until we got close."
"Not now."
"Turn off our lights."
"What? You want to be blind down here? I don't think so." Phil shook his head.
"Just the big headlights. We can still see close from the interior lights," said Anna.
"I can back off a bit." Phil frowned.
"No. I want to see if we can provoke a reaction."
"Why don't I just touch it with an articulator, then?"
"You might hurt it."
Mike reached over and turned off the exterior lights. "Enough," he said.
Outside, the strange tree-looking thing was dimly illuminated. They waited for long minutes, but nothing happened. "It's some kind of crystallized tower like the others, only a different shape," said Phil.
"We need to turn off the interior lights." Anna's heart was thumping hard in her excitement.
"How long?" asked Mike.
"A few minutes. It saw our lights and flashed at us, but stopped when we got close. I want to try something with this." Anna held up a small penlight she routinely carried with her on a ring with two keys and a flat, multiple-bladed screwdriver.
Phil shook his head, but Mike put a hand on his shoulder. "Five minutes, and no longer. Turn the lights out, Phil, and start counting."
The lights went out, and they were sitting in pitch-blackness. "This is really dumb," said Phil.
They waited one minute, then two. There was a faint scraping sound from outside that came and went, and nothing to be seen. Finally, Anna moved her hand close to the nose bubble and began flashing her little penlight off and on. She continued for half a minute, and then stopped.
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