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, right. Luciferase, an energy-requiring reaction she had done in a test tube a few thousand years ago in molecular bio lab. Glowworms—really fly larvae, she recalled—hung in long strands in New Zealand caves. She remembered a trip to the rain forest of Australia: some tropical fungi glow in the dark. Hmm. Will-o’-the-wisps in old graveyards, fox fire on old wooden sailing ships…could there be fungi here?
Damned unlikely. She couldn’t even get mushrooms to grow in the greenhouse. 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 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 got 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.
Gingerly she made her way up to the harness and yoke. It had been dumb to take them off, of course. But sometimes even stupidity paid off. She might have missed the luminescence if she hadn’t fallen, her handbeam knocked off.
Pulling herself up gave her time to think, letting the winch do the work. She could feel her excitement bum in muscles that seemed more supple than usual. Warmer here, for sure. She turned her suit heater down. Life hung out in the tropics.
Before she reached the tanks, she heard Marc’s impatient voice. “Julia, 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—”
“Handbeam 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—”
“Julia, calm down, you’re—”
“Turn off all your lamps.”
“What?”
“Turn ’em off. 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 lights off he could see it too. There was a long moment of utter shock. 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 Mars-mat.
“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. “My vent gas?”
“Uh-huh. Looks like it.”
“What a reaction. Damn! And fast!”
“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, a bit of nitrogen, and 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.” Julia straightened up carefully and backed away from the lesion.
