After a day, Liu summed it up. ‘I think it’s clear enough what happened here.’ He pointed at a sketch map of the site Stef had made on her slate. ‘There’s the lake bed. Dried up.’ It was a hollow littered by dead stems, and what looked like the ruin of a builder nursery; only native lichen and mosses survived here now. ‘No fancy migrating jilla here, eh, Yuri? So they left, thataway.’ These people had set off south, for reasons of their own, heading away from the substellar, maybe hoping to make it to the rim forest. The tracks could still be seen; they had marked the way with a few cairns. ‘Who knows where they are now? Or what became of them.’
‘Somebody will find out, some day,’ said Yuri grimly. ‘And will tell their families back on Earth, or wherever. Look, we’ve made our records. We’ll leave one of our markers in case we don’t make it back to the Hub. So this won’t be lost again. OK? Come on, let’s pack up and move on.’
On they travelled. Day after day passed, marked only by a human sleep cycle still slaved to light-years-distant Earth – that and the slow descent of Proxima in the sky, towards the north-west horizon, away from the zenith it occupied as seen from the substellar Hub. The shadows that preceded their two vehicles grew steadily longer, and as the dwarf star’s light struggled through thicker layers of air it frequently looked reddened, Proxima’s spitting flares and mottling of spots more easily visible to the naked eye. The air grew colder too; soon they couldn’t leave the rover’s heated interior without extra layers of clothing.
After more than forty days they reached a belt of rim forest.
Here they rested a day to stretch their legs and explore, while the ColU set out along the edge of the forest to seek a way through. Neither Liu nor Stef had seen such a forest before, and they wandered, wide-eyed, through its dimly lit, cathedral-like spaces, the slim stem trunks reaching up to those broad, patient triple leaves above. And they marvelled at the immense kites of the canopy, and the ferocious scavengers competing for the slightest fall of nutrient into the almost aquatic gloom of the forest floor. For Yuri, all this brought back memories of his earliest days on Per Ardua, when he had explored the forest of the northern reaches, so similar to this place, with the likes of John Synge and Harry Thorne and Pearl Hanks and Abbey Brandenstein, all long dead.
The ColU returned with news of a break in the band of forest, at a broad valley not far south of here. They returned to the rover and set off that way. The valley proved to be the relic of a glaciation, with a wide floor and steep walls. A river running from distant hills, substantial in itself, was dwarfed by the ice-cut valley across whose floor it meandered.
They followed the cut through the forest band, which proved to be quite narrow; soon it thinned out, leaving only isolated stands of trees.
In the more open landscape beyond the forest the driving was easy, along the gravel beds that lined the banks of the glacial valley. There were stem beds here, and kites flying, big, slow, ungainly beasts of a kind Yuri hadn’t seen before, and builders, slowly working on their middens and nursery bowers. The scene was bathed in the dim light of a lowering Proxima, with the faces of hills up ahead washed with a pinkish glow. Life here seemed sparse, tentative, starved as it was of energy. Yuri remembered in contrast the tremendous vegetable vigour of the Hub jungle at the substellar point.
The valley steadily narrowed as they worked their way upstream, towards a range of hills that were soon no longer so distant. The river’s source turned out to be a corrie, a huge scoop high up in a glaciated hillside.
Long before they reached that point Stef guided the rover away from the river and towards a pass through the hills, and beyond the pass they descended onto a plain. The shadows of the hills behind them now stretched far ahead, but they could see more ranges of hills marching off into the distance, with ice-coated peaks that gleamed in the dimming Proxima light and glaciers striping their flanks.
As they crossed the plain the ColU requested more stops. It took samples of the life forms it found in pools of permanent shadow, mostly slow-growing lichens in frosty patches feeding off a trickle of reflected light, protected from any motile scavengers by the very darkness that cradled them.
Once the ColU, digging, found what it called a rare, ancient fossil bed, saved from volcanic obliteration by some accident of uplift, which contained traces of creatures like builders but much taller, each with three long multi-jointed stem legs. These were creatures built for migration, for speed, the ColU argued. Perhaps these were relics of a transitional age, while the planet’s spin was slowing, but before it became fully locked in its synchronised day-orbit cycle. In such times, the ColU speculated, there must have been creatures that had migrated continually, keeping up with the slow passage of Proxima across the sky. Perhaps these ancestral builders had been among that throng. They discussed this, made some records, moved away.
They drove on, and on.
Close to the fiftieth-day halfway mark, Proxima touched the horizon at last. Now, Yuri knew, they would descend into the shadow of the planet itself.
In the days that followed Proxima descended with agonising slowness, its light ever more twilight red, its apparent shape distorted to obliquity by layers of the cool air, its lower rim sliced off by the horizon. Still there were a few stands of trees, an occasional kite flapping. But life here was dominated by the stromatolites. Some of them, huge, were oddly cup-shaped, their surfaces shaped like bowls to collect the drizzle of photons from the setting sun. Liu said they looked like natural radio antennae.
They didn’t get to see Proxima set fully. Before that point they drove into weather, seemingly unending storms, rain showers, fog banks, even snow blizzards. Stef argued that as the warm air of the starlit side spilled over into the cool of the dark side, it must dump all its water vapour as clouds and precipitation. The whole terminator, right around the planet, must be a band of semi-permanent snow and rain and fog, and they saw no more of the sky for a while. But they did see streams, rivers, some ice-flecked, flowing down the cloud-shrouded flanks of hills and uplands: the water delivered by the air from the day side, flowing back the way it had come. Thus, Stef observed, cycles of energy and mass would be closed, all around the terminator, the dividing line between night and day.
When they passed through the weather band and the sky cleared at last, the view was spectacular. Now they rolled through a sea of shadow that pooled at the feet of hills whose upper slopes were still in the light, shining above. Trees clung to these islands of illumination in the sky, with huge kites flapping lazily. Even further down the slopes life prospered, a secondary kind, pale, starved-looking creatures a little like crabs or segmented worms, all stem-based, which seemed to feed solely on the fall of dead leaves and other detritus from the higher ground.
Yuri felt stiff from the travelling, eyes rheumy, perpetually tired. Yet he was discovering wonders. ‘This stuff is wasted on three old fogies like us.’
The ColU asked for an extended halt. ‘Those summits are effectively islands. There could be unique biota up there, at least among the non-flyers, even the tree species. A whole array of unique ecosystems, in starlight islands all around the terminator.’
‘To be explored by somebody else,’ said Yuri gently. ‘We’ve got our own goals to achieve. Come on, ColU. I hoped you tested out your floodlights . . .’
So they went on, rushing past marvel after marvel.
They lost Proxima’s direct light at last. Now, under the cloudy skies that persisted near this terminator line, the only glow came from the pools of light cast by their own floods, and the rover’s brightly lit interior was a refuge from the dark.