A flicker from her handbeam brought her back. She looked down, shook it. The beam brightened again. Damn, not now.
The mat was thicker here, as she'd guessed it would be closer to the elusive source.
She landed on a wide ledge, moved briskly across it, mindful of time passing. The floor was slippery with Marsmat but rough enough so she could find footing. Sorry, she said silently to the mat, but I've got to do this.
Her handbeam flickered again, died. She shook it, bent her head to look at it with the headlamp, then felt a sudden hard blow to her forehead, heard the headlamp shatter. She fell backward, in slow-motion but inexorably, nothing to grab.
Her wrist hit first as she landed and she dropped the handbeam. She lay there for a moment, waiting for the surprise to go away. Must've run into an overhang. It was pitch dark. Where was her damned lamp? There was a faint glow to her left. That must be it. She started to get up, noticed a feeble luminescence ahead of her. Confused, she sat back down. Take this carefully. All around her, the walls had a pale ivory radiance. She closed her eyes, opened them again. The glow was still there. -No, not the walls-the Marsmat. Tapestries of dim gray luminosity.
She reviewed what bits she remembered about organisms that give off light. This she hadn't boned up on. Fireflies did it with an enzyme, luciferase, an energy-requiring reaction she had done in a test-tube a few thousand years ago in molecular bio lab. Glow worms-really fly larvae, she recalled-hung in long strands in New Zealand caves. She remembered a trip to the rainforest of Australia: Some tropical fungi glow in the dark. Hmm. Will-o'-the-wisps in old graveyards, foxfire on old wooden sailing ships ... could there be fungi here? Unlikely. Wrong model. She shook her head. Waves breaking at night into glowing blue foam during red tides in California. Those are phosphorescent diatoms. What else? Thermal vent environments ... Deep sea fish carried luminescent bacteria around as glowing lures. That's it. The lab folks had fun moving the light-producing gene around to other bacteria. Okay. So microbes could produce light, but why here? Why would underground life evolve luminescence?
Bing bing. The warning chime startled her out of her reverie. She flicked her eyes up. The oxygen readout was blinking yellow. Thirty minutes reserve left. Time to go back.
As she picked herself up she brushed against her handbeam. She picked it up but left it off. Navigating by the light of the walls was like hiking by moonlight.
Pulling herself up gave her time to think, excitement to burn in muscles that seemed more supple than usual. Yes, it was warmer here. She turned her suit heater down. Life hung out in the tropics.
Before she reached the tanks, she heard Marc's impatient voice. "Ann, where are you?"
"On my way. Pretty close." She rounded a jut in the vent walls, into the glare of his lights. The walls faded into black.
"Where were you? You're way late, damn it. The tanks were here on time-hey, where's your headlamp?"
"Ran into an overhang. Smashed it. Marc-"
"Handlamp too? What'd you do-grope your way back? Why didn't you call?"
He was clearly angry, voice tight and controlled. "I found, I found-"
"Ann, calm down, you're-"
"Turn off your lamps." ... Mat?" :,Turn off your lamps. I want you to see something."
"First we switch your tank."
She sighed. It was just like Marc to fuss over details. Looking down at the sidewalk for pennies and missing the rainbow.
When she finally got the lamps off he could see it too. There was a long moment of utter shock and he seemed to know it was better to say nothing.
Then she heard something wrong. The faint hissing surprised her. Mission training reasserted itself.
"What's that? Sounds like a tank leaking." Automatically she checked her connections. All tight. "Marc?-check your tank."
"I'm fine. What's the matter?"
"I hear something, like a leak."
"I don't hear anything.. ."
"Be quiet. Listen." She closed her eyes to fix the direction of the sound. It came from near the wall. She shone her handbeam on the empty tank, bent down low and heard a thin scream. Oxygen was bleeding out onto the Marsmat.
"Damn. Valve isn't secured." She reached down to turn it off. Stopped what?"
The Marsmat near the tank was discolored. A blotchy, tan stain.
"Damn! We've damaged it." She knelt down to take a closer look, carefully avoiding putting her hand on the wall.
"What happened?" Marc took one long step over, understood at a glance. "The oxygen?"
"Uh-huh. Looks like it."
"What a reaction. And fast! No wonder there was nothing in the first vent. You were right about that."
"Oxygen's pure poison to these life forms. It's like dumping acid on moss. Instantaneous death."
He looked around wonderingly. "We're leaking poison at them all the time in these suits."
She nodded. Stupid not to see it immediately, really. Like SCUBA gear, their suits vented exhaled gases at the back of the neck, mostly oxygen and nitrogen with some carbon dioxide. A simple, reliable system, and the oxygen was easily replaceable from the Return Vehicle's chem factory.
Marc shook his head, sobered. "Typical humans, polluting wherever we go."
"If the stuff is this sensitive, we'll have to be really careful from now on." Ann straightened up carefully and backed away from the lesion.
They stood for a long moment in inky blackness, letting their retinas shed the afterimage of the lamps. Finally Marc asked, "Where's the light coming from?"
"Marsmat glows. Phosphoresces, is more correct."
"How can it do that?"
"Don't know. The more interesting question is why."
They knew now that time and oxygen would set the limits. They had this day and were to return to the ship tomorrow. Team loyalty.
"Plenty of oxy up there," Marc said as they rested and ate lunch-a squeezetube affair she hated, precisely described in one of her intervideos as eating a whole tube of beef-flavored toothpaste.
"So we trade tanks for time."
"Piotr's gonna get miffed if we don't check in at the regular time."
"Let him." She wished they had rigged a relay antenna at the vent mouth. But that would have taken time, too. Tick tick tick.
"I don't want us to haul out of here dead tired, either."
"We'll be out by nightfall."
"We won't be so quick going out."
Field experience had belied all the optimistic theories about working power in low gravity. Mars was tiring. Whether this came from the unrelenting cold or the odd, pounding sunlight (even after the UV was screened out by faceplates), or the simple fact that human reflexes were not geared for 0.38 gee, or some more subtle facet-nobody knew. It meant that they could not count on a quick ascent at the end of a trying day.
"You want geological samples, I want biological. Mine weigh next to nothing, yours a lot. I'll trade you some of my personal weight allowance for time down here."
He raised his eyebrows, his eyes through his smeared faceplate giving her a long, shrewd study. "How much?"
"A kilogram per hour."
"Ummm. Not bad. Okay, a deal."
"Good." She shook bands solemnly, glove to glove. A fully binding guy contract, she thought somewhat giddily.
"Piotr's counting on using some of your allowance to drag back more nuggets and jewels, y'know."
"It's my allowance."
"Hey, just a friendly remark. Not trying to get between you two."
Innumerable nosy media pieces had dwelled on the tensions between a crew, half married and half not, complete with speculations on what two horny, healthy guys would feel like after two years in a cramped hab with a rutting couple just beyond the flimsy bunk partition. All that they had scrupulously avoided.
So far the answer was, nothing much. Raoul and Marc undoubtedly indulged in gaudy fantasy lives and masturbated often (she had glimpsed a porno video on Raoul's slate reader) but in the public areas of the hab
they were at ease, all business.
There was no room for modesty in the hab, four people in a small condo for two years. So they unconsciously adopted the Japanese ways of creating privacy without walls. They didn't stare at each other, and didn't intrude on another's private space unless by mutual agreement.
Nobody had thought much about what the hab would be like if the newlyweds-well, it had been well over two years now, most of that time in space got into a serious spat. Maybe on the half-year flight home they would find out. She would worry about that then; for right now "Hey, we're eating into my hard-bought hours."
They returned to the ledge where Ann had her accident, two hundred meters farther in. On the other side of the fortuitous overhang they found a pool covered with slime on a ledge. It was crusty black and brown stuff and gave reluctantly when she poked it with a finger.
"Defense against the desiccation," she guessed.
Marc swept his handbeam around. The mat hung here like drapes from the rough walls. "Open water on Mars. Wow."
"Not really open. The mat flows down, see, and covers this pool. Keeps it from drying out. Saving its resources maybe?"
She scooped out some of the filmy pool water and put it under her hand microscope. In the view were small creatures, plain as day.
"My God. There's something swimming around in here. Marc, look at this and tell me I'm not crazy."
He looked through the 'scope and blinked. "Martian shrimp?"
She sighed. "Trust you to think of something edible. In a pond this small on Earth there might be fairy shrimp, but these are pretty small. And I don't even know if these are animals."
She hurried to get some digitals of the stuff. She scooped some up in a sample vial and tucked it into her pack. Her mind was whirling in elation. She studied the tiny swimming things with breathless awe.
So fine and strange and why the hell did she have to peer at them through a smudged helmet? They had knobby structures at one end: heads? Maybe, and each with a smaller light-colored speck. What?
Could Mars life have taken the leap to animals-a huge evolutionary chasm?
These could be just mobile algal colonies-like volvox and other pond life on Earth. Whatever they were, she knew they were way beyond microbes. She bent down over the pool again, shone her handbeam at an angle. The swarm of creatures was much thicker at the edges of the Marsmat-feeding? Or something else?
She couldn't quite dredge the murky idea from her subconscious. The arrangement with the mat was odd, handy for the shrimp. What was the relationship there? Some kind of symbiosis? And how did the swimming forms get to the pool?
They climbed down from the ledge. As they descended, the mist thickened and the walls got slick and they had to take more care. The cable was getting harder to manage, too. She could not stop her mind from spinning with ideas.
On Earth, hydrothermal vent organisms kilometers deep in the ocean photosynthesized using the dim reddish glow from hot magma. The glow becomes their energy source. Could some Martian organisms use the mat glow? Wait a minute-the "shrimp" had eyes! Or did they?
"Marc, did you notice anything peculiar about the shrimp?"
He paused before answering. "Well, I don't know what they should look like. They looked sorta like the shrimp I feed my fish at home."
"Did you notice their eyes?"
"Uh .. ."
"The knobby ends, those had lighter specks, remember?"
"Yeah, what about them?"
"So you saw them too."
"Why, what's the matter-Oh."
"Right!"
"I see, they shouldn't have eyes."
"Good for you. I'll make a biologist out of you yet. On Earth, cave-dwelling organisms have lost their eyes. Natural selection forces an organism to justify the cost of producing a complicated structure. You lose 'em if you don't use em. "So if they have eyes-"
"On Earth, we'd say they were recent arrivals from a lighted place, hadn't had time to become blind."
"But that's impossible. The lighted parts of Mars have been cold and dry for billions of years. Where would they have come from?"
"I agree. So my next choice is that it's not dark enough here to lose the eyes. But the idea of some kind of transfer with the topside peroxide microbes is worth thinking about."
"That glow is pretty dim."
"To us, maybe. We're creatures from a light-saturated world. Our eyes aren't used to these skimpy intensities. Closest parallel on Earth to these light levels are the hydrothermal vents. There are light-sensitive animals down there, even microbes able to photosynthesize."
"Maybe they're not even eyes."
"They're light-sensitive. The critters clustered under the beam from my scope.
"Wow."
"I need more information, but at the very least it suggests that the glow is permanent, or at least frequent enough to give some advantage to being able to see. And that means there should be something that can use the glow as an energy source. Maybe the mat is symbiotic-a cooperation between glowing organisms and photosynthesizers?"
"Yeah ... That suggests the glow is primary. What's it for?"
"Don't know, just guessing here."
"Curiouser and curiouser, as Alice said."
"I didn't know boys read Alice in Wonderland."
"It seems to fit what we're doing."
"Down the rabbit hole we go, then."
Below the level of the pool ledge were twisty side channels to the vent. These ran more nearly horizontal, and they explored them hurriedly, clumping along until the ceiling got too low. No time to waste crawling back into dead ends, she figured. They headed back to the main channel and then found a broad passage that angled down. It was slick and they had to watch their footing.
The mats here were like curtains, hanging out into the steady stream of vapor from the main shaft of the vent. Some seemed hinged to spread before the billowing vapor gale. Ann was busy taking samples and had only moments to study the strange, slow sway of these thin membranes, flapping like slow-motion flags. "Must be maximizing their surface area exposed to the nutrient fog," she guessed.
"Eerie," Marc said. "And look how wide they get. There's a lot of biomass here-wonder if any of it's edible."
At turns in the channel the mats were the size of a man. She took a lot of shots with her microcam, hoping they would come out reasonably well in their lamp beams. The mats were gray and translucent. Under direct handbeam she could see her hand through one.
How did these fit in with the peroxide-processing microbes on the surface?
Clearly these mats harvested vapor; did they somehow trade it with the peroxide bugs, water and methane for the racy stim of peroxide? She had a quick vision of an ecosystem specialized to use what it had: peroxides aplenty above, and ice below, awaiting a lava flow to melt it.
Did life negotiate between these resource beds? Oxides cooked by the scaring sun, with microbes specialized to gather their energy. Those microbes must have evolved after the great dryness came, when UV sizzled down and drove deeper all that could not adapt to it.
Yet below, where water still lurked, dwelled forms that owed their origin to the warm, moist eras of the Martian antiquity.
The mats-and what else, in such labyrinths as this, all around the globe-transacted their own business with the peroxide eaters. They could harvest the moisture billowing from beat below, and perhaps melt the permafrost nearby. At the edges of Earth's glaciers lived plants that actually melted ice with their own slow chemistry.
The thermal vents and their side caverns could be extensive. With an exposed surface area as big as Earth's, there was plenty of room for evolution to experiment.
Nothing like this pale ivory cavern on Earth, ruled as it was by boisterous, efficient aerobic life. To escape the poisonous reach of oxygen, anaerobes retreated to inhospitable niches like hot springs and coal mines. In that infertile ground they survived, but remained as microbes, spawning no new forms. On Mars, any oxygen-loving forms would hav
e died out when the planet lost its atmosphere. Here the anaerobes persisted, and evolved new forms; maybe the closest analogy was to the marsupials in Australia. Marsupials breed more slowly than true placental animals, and thus were eliminated all over the Earth except for the huge island of Australia. Free of competition, they populated an entire continent, evolving completely unique forms such as kangaroos, wombats and the duckbilled platypus. What were the equivalents on Mars?
Ann gently caressed a mat as it lazily flowed on the vapor breeze. Plants, flourishing in the near-vacuum. She could never have envisioned these ... Yet in the edges of her vision she sensed something more. She thought for a moment and said, "Turn off your lamps."
"Mine's getting pretty low," he remarked as they plunged into blackness.
The glow gradually built up in their eyes. "There's a lesion on the closest mat," said Marc.
She swung gently over, peered at it. "It's the same shape as the damage we did above." The mat around the wound shape glowed more brightly with pale phosphorescence. It seemed to be changing as she watched. "Look at it out of the corner of your eye," she said. "See?"
"It's spreading downwards."
The mats were growing ever larger as they went lower. She leaned over into the vent and peered around. "The glow increases below." They looked down the vent.
"It's definitely brighter down there."
"Let's go." They descended carefully, playing out line. Their lamps washed the mats in glare that seemed harsh now. Twenty meters down she said, "Lamps off again," as they rested on a shelf. When her dark vision came back her eyes were drawn to a splotch of light. "Damn! How-?"
"It's the same shape again."
"A mimicking image. Parrots imitate sounds, this mat imitates patterns posed on it, even destructive ones. Why?"
He drawled, "I'd say the question is, how the hell?"
"The mat here learned about the wound above."
"Okay, they're connected. But why the same shape?"
She sighed. "It's a biological pictograph. I have no idea why, but I am sure that any capability has to have some adaptive function."
"You mean it has to help these mats survive."
The Year's Best Science Fiction: Fifteenth Annual Collection Page 100