In 2012, for the first time, Space Day was observed on Mars. The celebration was simple: The crew slept in past noon and spent the afternoon in blissful idleness. In the evening they assembled in the galley to teleconference with Mission Control.
"You've got to stop this maniacal effort," flashed Chief of Operations Mason's video image. "It's no good. You're killing yourselves, and it's not working. Our calculations show that you're way behind on making enough fuel to launch by the time the 2013 Earth return window closes, and at this rate you'll all be dead long before the 2015 window opens. You've got to call it quits. Trust me, a resupply mission is in the works. Leave it to us."
Townsend looked at McGee, who just shook his head. In disgust, the colonel switched off the TV.
Gwen spoke up. "It's not over yet, Colonel. Maybe our present rate is too low, but the soil's getting wetter deeper down. We still might make it."
The commander turned to his geologist. "Luke, is it possible?"
The Texan didn't have the energy to argue. "No. We're too far behind for that to make a difference."
Rebecca slumped in her chair, feeling weak. "It's my fault. All my fault."
Townsend said, "We all agreed with the decision, Doctor. And we're no worse for trying." He stretched his aching back. "Not much, anyway."
"You don't understand." Rebecca shuddered, then appeared to gain control. "In order to maintain the crew's strength over the past several months, I increased the rations drawn from the Beagle's reserve. Well before the 2015 return window opens, we'll have nothing left to eat but the greenhouse output, and that's only enough for three. Max."
McGee decided to lift their spirits with a joke. "Hmm. Just how did the folks at Donner Pass decide who got to be hors d'oeuvres?" It didn't work. Met with scowls from the others for his black humor, the professor retreated. "Okay, another stupid mistake. When will I ever stop putting my footnotes in my mouth?"
Townsend didn't like the way the conversation was going. "Let's get this straight. I'll be damned if I'm going to pick straws or flip coins to see who lives or dies. It's not the American way."
"It may soon become our only rational choice," Rebecca said icily.
Gwen fumed. "I don't care about what an atheist bitch calls ‘rational choices.'"
"Major, please!"
Rebecca's face reddened, but otherwise she appeared to ignore Gwen's outburst. "Colonel, the greenhouse is filled to capacity, as is all available space on the Hab's lower deck. The only potential space we're not using is the interior of the pressurized rover." She shrugged. "If we decide to convert the rover into a stationary greenhouse, that might add enough output to allow one more person to survive. Maybe."
"Bad idea," Luke commented. "We need the rover."
The biologist was puzzled. "For what?"
"For prospecting." Now everyone gave him puzzled looks. "Look, we've been going about things the wrong way, processing large volumes of low-grade ore, when we should've been searching for the mother lode."
"What do you mean, mother lode?" Townsend asked.
"A concentrated source of liquid water."
Townsend looked quizzically at the geologist. "There can't be any liquid water on Mars. Even I know that. It's much too cold."
"On the surface, yes. But underground..."
Rebecca grasped the concept instantly. "So you believe in the existence of a subsurface Martian water table?"
Luke seemed almost apologetic. "I didn't used to, but the dating of some of my igneous samples shows volcanic action in Tharsis as recently as forty million years ago—in other words, back just one percent of the age of the planet. Might as well be yesterday."
"So... that means Mars has a hot core, like Earth?" McGee asked, trying to understand the implications.
"Right. And if the core is hot, then at some depth it must be warm enough for liquid water to exist. It's got to be there, somewhere, because the north polar cap is a low-elevation ice field that almost certainly continues underground as the terrain rises in the Borealis and Acidalia regions. Now, since subsurface ice is stable only above latitudes of about forty degrees—"
Sensing an incipient lecture, Townsend interrupted: "How deep would we have to drill?"
Luke rubbed his chin. "Around here, a kilometer, maybe two."
Dammit, another fantasy scheme. Townsend shook his head pessimistically. "That's much too deep. Our drilling rig only has a reach of a hundred meters."
"I could double that by hooking the spares in series," Gwen offered.
"Still way too short."
Luke was undaunted. "True, but if we drive the rover down to the lower elevations in Xanthe Terra, the water might be much closer to the surface. We'd need to find a place that has a surface regolith layer of anomalously low thermal conductivity lying over a subsurface layer of high porosity."
Even with his limited knowledge of geology, McGee realized the Texan was describing a long shot. "But something like that has got to be a rare occurrence. We can't drill everywhere. How are we going to find it?"
"Electromagnetic sounding. Send low-frequency radar signals down into the ground. If there's water there, the bounce back will tell you."
Simple enough, Gwen mused, provided we can produce the right type of signal. "What frequency?"
"You can generally get down about ten wavelengths, so we'll need a twenty-meter signal."
"Twenty meters, that's fifteen megahertz, HF band," Gwen thought out loud. "Our over-the-horizon radios can access that frequency. I could rig up a quarter wavelength downward-pointing Yagi antenna and attach it to the rover, and put a pulsed modulator on the power amplifier. Then, as we drive along, we—"
"—do some honest prospecting," Luke concluded with a smile.
The colonel was far from convinced. "Now hold on, I've had a bit of experience with ground-penetrating radar in military applications. It's easy to get all kinds of false positives."
"True, we'll probably end up drilling ten dry wells before we hit the real McCoy. But with luck, sooner or later we'll find it. It's a gamble, sure, but I don't see how we have a whole lotta choice."
So now we're relying on luck, Townsend thought. "If we're going to make the launch window, it better be sooner."
Rebecca quickly parameterized the problem. "The probability of a quick find would rise in direct proportion to the intensity of the search."
McGee understood. "So we drive the rover fast and cover a lot of miles. But that means we burn a lot of fuel."
Luke was undeterred. "The ERV's tanks are over one-fifth full. We've got lots of fuel if we tap into that."
"Out of the question," the colonel said firmly. "That propellant is part of our ticket home. Think of all our hard work so far. We can't make the 2013 return window, but if we keep adding to it we can have enough to launch for Earth when the 2015 window opens."
"The three of us still alive, you mean," Gwen commented dryly.
Townsend began to feel confused. "It's a reckless gamble."
Sensing Townsend's weak spot, Gwen pressed the point. "All of us or none of us, Colonel. Isn't that what you said?"
"That was just betting greenhouse margin and wasted labor," he explained. "We knew there was moisture in the soil, and that bet paid off. We now have a way to get home."
"Some of us," Gwen said flatly.
This is so irrational, Townsend thought. "You're asking me to throw away all the work we've done, the only chance we have, on wild speculation." He turned to Rebecca. "Dr. Sherman, you're a scientist. Using your logic and not your emotions, do you really believe in this near-surface water-table theory?"