Soon, she managed to settle into a steady rhythm, with each step jerking the sled free of the gumbo which clutched at it.

Every instinct told her that Rosenberg’s billion-year scheme couldn’t work.

It was, of course, a typically arrogant technocratic fantasy — in a way an extension of the gigantic, ludicrous journey they had undertaken to come here — to suppose that it would be possible, with a handful of micro-organisms thrown into a lake of ejecta melt, to reach out across billions of years and shape the evolution of a world.

For instance, Rosenberg had made a lot of assumptions about the viability of bacterial spores over such huge deserts of time. And who could really say what the future evolution of the sun would be hike? Nobody had actually watched a star follow through its ten-billion-year evolutionary cycle, from birth to death; every theory was inferred from humankind’s mayfly-like snapshot perception of the stars that happened to be scattered through the universe today. Maybe the red giant sun would grow so huge it overwhelmed Titan, boiling away its atmosphere in moments. Or maybe the sun would just go nova, blasting Saturn and its ancient moons to fragments…

It was, she thought, a pretty dumb plan.

But, in the end, it gave her a goal.

Thus her life would end, she thought: struggling to fulfil another project, one more technological dream, because she had nothing better to do.

After a few paces she looked back. Tartarus Base was already lost in the thickening orange haze, the deepening gloom of Titan twilight.

After forty-eight hours, the last light had leaked out of the orange haze layers.

Benacerraf walked through the dark, fighting the resistance of the invisible gumbo as it sucked at her sled and snowshoes. All she could see was the splash of lamp-light on the glistening gumbo hide ahead of her, its diffuse reflection from her own nose and eye ridges, the ancient bone structure of her own human face.

Titan was a world of, enclosure.

She lost track of time, of the day-night cycle of the distant Earth. She would check her Rolex in the light of her lamp, and find that ten, or twelve, or fourteen hours had worn away, as she had driven on through her tunnel of blindness, dark save for the splash of light from her helmet lamp, silent save for the scratch of her breathing, the whir of fans and pumps in her backpack, the muttering of her own voice.

…She brooded. What if Rosenberg had been right, in his worst-case projections?

What if the clouds had rolled over the face of Earth — what if she was, truly, the last spark of awareness in the Solar System?

There were theories that consciousness was a quantum process. That reality — the Universe itself — was called into existence by conscious minds, as, by observation, they collapsed the infinite possibilities of each quantum wave function into a single, definite event, embedded in history.

The Universe, it was said, needed consciousness to create itself.

Then what if she was the last?

Here she was in this bubble of darkness, the limits of her personal cosmos reaching no more than five or six feet in any direction. Was there anything beyond the intangible walls of the hazy dark? Did she call into existence new stretches of the gumbo as she walked over them?

If she did not look at the Earth, did Earth any longer exist?

And when she died, as the last bit of consciousness departed, would the world — Titan and ringed Saturn and the remote sun and Earth and the stars — would all of it fold away and dissolve, with the cold grey light underlying creation breaking through, like, a projector’s lamp through a trapped and burning film frame?

At times she felt more frightened than she’d ever been in her life.

She welcomed the familiar pain of the harness pressure points and in her feet. The pain gave her something to think about, outside her own sterile thoughts.

She made camp, proceeding slowly and carefully, double-checking every step before she trusted herself to crack the seal of her suit.

She cleaned herself out. She felt free to dump her bags of frozen urine and feces rather than haul them with her. She tended clumsily to her various wounds and injuries.

She developed another big, ugly abscess, this time on her right foot around the ankle, where a flaw in her boot had rubbed and caused her skin to blister. She decided she had to lance it. She took a sterilized scalpel, closed her eyes and stabbed at the abscess, letting the momentum of her bunched fist ram the blade into her flesh. The pain was extraordinary, sharp and penetrating, much worse than when Rosenberg had operated on the same kind of injury.

When she looked down, pale, watery pus was leaking from the wound. She squeezed out as much matter as she could, and wiped the incision with a scrap of parachute fabric. Then she dosed it with antiseptic fluid and dressed it.

She ate from a packet of reheated soup, and drank melted Othrys water. Then she sealed up her suit and lay down against the plastic tent wall, layers of parachute fabric beneath her.

She propped her photographs in front of her helmet. She stared into those fragments of bright Seattle daylight, trying to believe she wasn’t alone, as she waited for sleep to claim her.

She made rapid progress.

She reached Cronos, and crossed its rim of pressure ridges. She skirted the walls of the crater they’d called El Dorado.

She walked into Titan’s murky daylight once more.

Beyond El Dorado, high on the gumbo-stained ice plateau of Cronos, she came to a ridge of broken, jumbled ice, maybe twenty feet tall. She had trouble hauling her sled over this; several times she had to go back and grab the lip of the sled, dragging it bodily up and over.

When she reached the crest of the ridge, she was facing a plain that looked as if it had been crudely assembled from jammed-together blocks of ice. Pressure ridges criss-crossed it.

The persistent, bone-deep cold seemed to recede. It was warmer here.

She descended the ridge, and began to make her way over the plain. The blocks and upthrust ribs in the ice were a foot or more high, and frequently snagged the runners of her sled. The ice creaked and shuddered; evidently great plates of it were sliding over each other in vast tectonic evolutions. She had the sense of riding the scaly hide of some huge, sluggish animal. But that elusive warmth seemed to gather.

She stopped. With the edge of her ski she scraped away the thin layer of gumbo and loose ice crystals from the surface.

The ice seemed thin: perhaps a foot thick, or even less. She thought she could see a dark liquid beneath the complex flaws of the ice, and bubbles of some gas trapped there.

At last she came to a dark break in the ice surface. It was a lead, a stretch of open water, within a crack in the ice maybe six inches deep. The water was dark and scummy, polluted with tholin and hydrocarbons.

“Hot damn,” she said. “You were right, Rosenberg. I wish you could have gotten to see this.”

She loosed her traces and leaned clumsily over the lip of the crack. She dipped one gloved hand in the water. Immediately the cold penetrated the layers of her glove, and the heater diamonds stung her flesh. Close to its freezing point, the water was a hundred and seventy degrees above the ambient temperature.

Water was molten rock here. It was as if some suited monster had come to Earth, and dipped its hand into the scalding red-hot lava stream of a volcano. But she was the alien, here on Titan.

She lifted out her hand. Away from the water surface the air temperature dropped quickly, and the droplets of oily water that clung to the fabric of her glove spread and froze, turning to frost patterns. When she closed her fist the frost crackled and broke away, hard ice fragments falling back to the water’s dark surface.