She wondered how long she’d been out here.
She felt as if her sense of time was dissolving, stretching like melted candle-wax. Pendulums would swing more slowly here, like the rocking of her boat, in the gentler gravity. Perhaps some pendulum hidden deep in her own being was slowing, too, in response to this small world.
But now Rosenberg waved. He had set up the small TV camera on its stand, looking out at her. And the portable antenna pointed straight up, to where Cassini hovered far above the clouds and haze in its fifty-thousand-mile Clarke orbit.
The comms gear was a reminder that this wasn’t some dumb jaunt on a lake. She was out here to look for amino acids and other good stuff. And this was a NASA extravehicular activity, on the surface of an alien world; they had a duty to return data on what they were doing, whether anybody was listening or not.
Anyhow, she thought, this is the first time in all of human history that a grandmother has gone boating on the surface of a low gravity moon. It ought to be on TV. Jackie should see this. And the boys, she thought wistfully.
She began the series of experiments Rosenberg had set out for her. The first was a series of sample collections; she gathered up droplets from the lake into plexiglass test tubes, and bottom sediment that she trawled up using tubes fixed to a line.
She started up the tilt meter. This little gadget was something like an electronic spirit level. It contained two vials of a conductor fluid; as the boat tipped back and forth under the influence of the lake’s slow waves, the electrical resistance of the fluids in the tubes changed, and could be measured. Next she dipped a refractometer into the liquid to measure its speed of light. The refractometer was a cute thing, a little transparent box with prisms inside it, which she filled up with Clear Lake fluid. She measured the fluid’s ability to conduct heat; by filling up a tube with fluid she immersed a platinum wire, and watched how its resistance changed as she passed current through it. She deployed a simple gadget which measured the speed of a sound wave travelling between two piezoelectric transducers. The sound speed would tell a lot about the ocean, and when she reconfigured the gadget, Benacerraf might be able to make a sonar estimate of the depth of the lake, if the grunge-coated bottom proved reflective enough. She measured the ethane’s dielectric constant — its ability to hold an electric charge — by filling up a plate condenser with fluid, and measuring its capacitance. And so on.
One of Benacerraf’s favorite instruments was a pair of thin metal vanes mounted on a piezoelectric crystal. The crystal drove the vanes, and their resonance depended on the density of the fluid in which they were immersed.
The results of the experiments ought to help determine more about the lake’s nature. The lake wasn’t a simple pool of ethane. There were fractions of other paraffins — methane, propane, butane, others — as well as dissolved nitrogen, and a slew of higher organics. For instance, the refractive index of the lake fluid was very sensitive to the percentage of dissolved methane.
She had to bend over the side of the boat to work, and soon her back was aching once more. She tried to keep her hands clear of the cryogenic fluid of the lake itself. She worked with tongs and pipettes, as if dealing with some acid. She fumbled a little with her gloved hands.
Her last experiment was a plumb line, pleasingly crude and intuitive, just dropped over the side. The line was loaded with a scrap of Command Module aluminum, and the depth was marked out by simple knots in the steel cable. It was a little hard to tell when the string was fully paid out, so soft and muddy was the bottom. When she estimated the weight had reached a reasonably firm surface, she read off the depth. Ten feet.
She described the result, and what she could see, to Rosenberg.
“That’s good, Paula,” he said. “The ethane is deposited at a rate of three feet every ten million years. So that makes your lake maybe thirty million years old, which is pretty young for a crater of such size. When it formed, the crater would have had the kind of shape we recognize on the Moon — a shallow saucer, with maybe a central peak. After that, the ethane lake gathered. But the bedrock ice on Titan flows, on the timescale of a few million years. Viscous relaxation. That pushed up the center of the crater into that ice dome you see. So the ethane was shoved into an annulus, a ring around the domed mountain…”
“And the horseshoe shape?”
“Saturn’s tides. If Titan was covered by an ocean, the surface would be drawn into an egg shape by Saturn’s gravity, with the sharp ends pointing towards and away from Saturn. Our isolated lake is a fragment of that egg-shaped surface. It’s as if the crater is tipped up a little bit; all the fluid is pushed to one end of the annulus channel by the tidal acceleration.”
Benacerraf felt awed. She looked around at the horseshoe shape of the lake once more. Saturn was invisible, but its gigantic influence was everywhere, its gravity field shaping the very nature of the landscape over which she moved. Benacerraf felt tiny, irrelevant, as if cupped in the palm of huge, invisible forces.
On impulse, she bent, stiffly. She got hold of the lip of the boat’s wall, and got down to one knee. Immediately she could feel the cold of the hull, and of the mass of ethane below: it was as if the heat was being drained out of her body through the bone of her knee, the layers of her suit, and she could feel the hot, ineffectual triangles of her laboring suit heater.
She leaned out of the boat, and looked into the ethane. Fat ripples, concentric with the circumference of the boat, oozed across the surface of the lake, suffused with the slow time of Titan. The ethane was utterly black, returning no reflection of her helmet, her face. It was unnerving, as if this wasn’t a liquid at all; it was as if she was poised over a hole in the world, a pit of black space that stretched down to infinity.
She reached out with a gloved hand. She passed her fingers through the ethane. In her peripheral vision she could see that a warning light flashed on her chest panel.
She pulled her hand out of the lake.
She lifted up her glove. The residual ethane gathered into fat little globules on her fingers and palm; its high surface tension had pulled it into these light, mercury-like balls. Set against the blue of her glove, this sample of the lake was a kind of dull brown, but not completely opaque, like dirty petrol. She thought she could see particles, swirling about in the interior of the globules, but the light was poor.
Even as she studied the globules they were shrinking. The boiling point of pure ethane was around ninety below — which was about ninety degrees above the ambient temperature. It was a big temperature jump, but even so, so quickly, the ethane droplets were absorbing the heat which was leaking out of her suit. The rapid evaporation was disturbing, a tough reminder of the fragility of her situation here. And every molecule of ethane that left her hand would carry away a little more of the heat her body needed.
She shook her hand free of the remaining droplets; they scattered from her glove in slow-motion parabolic arcs.
When she looked at her hand again, she found that the evaporating ethane had left a purplish scum on the fabric, in little discrete spots. Complex, prebiotic hydrocarbons: once more, she was immersed in the stuff of life.
“Paula,” Rosenberg called now, urgency in his voice.
“What?”
“Take a look up there. The clouds.” Benacerraf had to tilt back on her heels to see. The methane clouds were still more broken now, and were streaming, across the orange haze ceiling beyond.
“Wind coming up,” she murmured. “That was sudden. What do you think, Rosenberg? Fifteen knots?”