Valentina nudged him and pointed. Over the horizon, a geyser was erupting. It was the source of the snow.

The sparkling plume, tens of kilometers high, was venting into space. The plume was blue, sulphur dioxide. At the top of the plume the ice glittered brightly: Ionized by Jupiter’s magnetic winds, the charged molecular fragments shimmered with energy, a miniature aurora. At the base of the plume, lava was flowing. Perhaps it was liquid sulphur. As it emerged it flowed stickily, slowly, like molasses, but as it cooled it became runnier, until it pooled down the shallow slopes of the vent like machine oil.

A volcanic plume, glowing in the dark. It looked like a giant, twisted fluorescent tube: exotic, strange, spectacular. His heart lifted, the way it had when he first beheld Alpha Centauri. He might not understand everything he saw. But, he felt now, it was worth coming out here — worth exploring, worth suffering all the incomprehensible shit and endless culture shocks and even getting slapped around by Neandertals — worth it for sights like this.

The march was diverted to skirt the plume’s caldera.

Soon the party started to stray into an area where a kind of frost lay over the ground, thick and green-blue, probably sulphur dioxide. The ground started to get significantly colder under Malenfant, and he was shivering.

The party moved away from the frost, seeking warmer ground.

They were walking over hot spots, he realized. But the hot spots must shift. Io, plagued by volcanism, squeezed like a rubber ball in a fist by Jupiter’s tidal pumping, was resurfaced by lava flows all the time.

So the Neandertals had to move on, wandering over Io, in search of warmth from the ground.

It was one hell of a lifestyle. But they seemed to be happy.

About twice every Io day the caravan stopped.

The Neandertals didn’t always set up camp. They would unload scuffed and scarred pieces of equipment, boxes the size of refrigerators or washing machines. They plugged their magic suits into these, at hip and mouth, for a couple of hours at a time. The mouth socket supplied food, edible mush that tasted of nothing.

Malenfant didn’t know how his magic suit kept him supplied with oxygen; he wasn’t carrying a tank. The suit must somehow break down the sulphur dioxide air and scrub out carbon dioxide from his lungs. Maybe the hip socket extracted stored waste, carbon dioxide and urine and fecal matter, for recycling. Anyhow the boxes seemed to recharge the magic suits, making them good for another ten or twelve hours.

The suits just worked, without any fuss. But the Neandertals only had a finite number of magic suits, and seemed to have no way of manufacturing more. If some sad old geezer hadn’t died, there would have been no magic suit for Malenfant. What then? Would they have abandoned him? Well, he hadn’t been invited here.

He had no idea how old all this equipment was. It was clear to him somebody had set up this Neandertal community on Io. Somebody. The Gaijin, of course. Who else?

He had yet to figure out their purpose, however.

Every time the Neandertals stopped they checked over the Staff of Kintu.

This was a metallic rod, about the size of a relay baton. It seemed to be their most precious artifact. It was just a pipe a half meter long, of a metal that looked like aluminum, and it seemed light. Sitting in Io frost, the adults would pass the Staff from hand to gloved hand, checking its weight, fondling it, signing over it. The songs they sang, about the breath of Kintu, concerned the Staff. Maybe it was some kind of religious totem. But it was too easy to assume that anything you didn’t understand must have religious significance. Maybe there was more to it than that.

Malenfant envied them their community. Ignored even by the children, he felt shut out, lonely. He felt eager to learn to talk.

Malenfant observed signs, copied them, and repeated them to Valentina.

At first he had been able to grasp only simple concrete nouns, straightforward adjectives: a hand raised to the mouth for “food,” for instance, or a rubbed stomach for “hungry.” But, more slowly, he learned to recognize representations of more abstract thoughts. Two forefingers brought together harmoniously seemed to mean “same” or “like”; two pointing fingers stabbing each other was “argument” or “fight.” There seemed to be a significance in the hand shapes, their position relative to the body, and accompanying nonmanual features like body language, posture, and facial expression. And there was a grammar, it seemed, in the order of the signs. Get any one of the elements wrong and the sign made no sense, or the wrong sense.

It seemed to him that several signs could be transmitted at once, using fragments of multiple words. The Neandertals were not constrained to speak linearly, a word at a time, as he was. They could send across whole chunks of information simultaneously, at a much higher bit rate than humans. And, it occurred to him, these new reconstructed Neandertals must have devised their rich, complex language from scratch, in just a few generations. After all, there could be no way of retrieving the lost language of their genetic predecessors, the true Neandertals.

It was a wonderful, rich mode of communication.

He tried to avoid getting slapped. But he was punished if he got the signs too badly wrong.

“You don’t know your own strength. I’m an old man, damn it!”

Slap.

When the Neandertals lay down to sleep, out in the open, they did it in their magic suits, out there on the bare surface of Io.

He picked out the constellations — and the pale stripe of another comet, a huge one, its double tail sprawled over the sky. And in the direction of Orion there was something new: bright flares, like distant explosions, scattered over a shield-shaped patch of sky. It was a silent, unending firework show, as if there was a battle going on, out there at the fringe of the Solar System, a defensive fight against some besieging invader.

War in the Oort cloud, perhaps. Were the Gaijin battling Nemoto’s star-cracking aliens out there, on the rim of the system, defending Sol? If so, why? Surely the Gaijin’s motivation had little to do with humanity. If they fought, it was to protect their own interests, their projects.

And, of course, if there really was a comet-scrambling war going on in the Oort cloud, it had one dread implication: that the Crackers were no longer out there, at Procyon or Sirius, but here.

Sleep came with difficulty under such a crowded, dangerous sky. In the end he burrowed under his bulky NASA pressure suit, seeking darkness.

After maybe a week, to Malenfant’s intense relief, they set up camp once more. It was at a site that had evidently been used before: a rough circle of kicked-up soil, scarred by hearths.

Inside the teepee the Neandertals immediately stripped off. After a week locked into the suits the stink of their bodies almost knocked Malenfant out.

There was a great spontaneous festival of the body. The kids wrestled, the adults coupled. Malenfant saw one girl pursuing an older man — literally pursuing him around the cave, her vulva visibly swollen and bright red, until she’d pinned him down and climbed on top of him. Then they slept together, in great heaps of stinking, hairy flesh. There was no lookout; presumably there were no predators on Io, no enemies.

Malenfant hunkered in a corner, generally ignored, though Valentina and Esau brought him food.

Sometimes — when the light was low, when he caught a woman or child out of the corner of his eye — he thought of them as like himself, like people. But they weren’t people. They were no better or worse than humans, just different — a different form of consciousness.

It seemed to him that the Neandertals lived closer to the world than he did. That intense physicality was the key. Their consciousness was dispersed at the periphery of their beings, in their bodies and the things and people that occupied their world. When two of them sat together — signing or working in peaceable silence — they seemed to move as one, in a slow, clumsy choreography, as if their blurred identities had merged into one, in the ultimate intimacy. Malenfant felt he could see the flow of their consciousness like deep streams, untroubled by the turbulence and reflectiveness of his own nature.