Something sleeps in the ice

This life evolved in the dark ocean of Hearth, the Interloper's largest moon, warmed by tides that rose and fell over centuries. Every cold epoch killed anything that could not go dormant, so its whole biology is built around waiting: freezing solid, surviving vacuum and radiation, and waking when warmth and water return.

That is how it survived being blasted off Hearth inside rock. It has been sitting dormant in frontier ice for 150 years.

The Sun and the Interloper formed in the same birth cluster, and in those early days rock could have carried life between them. Hearth life and Earth life turn out to share a single origin about four billion years ago. They use the same chemistry and read the same genetic code, which is why the rime can take in Earth genes.

The rime and the intelligent aliens are one form of life in different states. Think of a fungus: the rime is the mycelium, the slow, frost-like body spreading through rock and ice, and the aliens are its fruiting bodies, grown when conditions are right and taken back in when the season ends. Humans name the stages as they meet them.

1. Rot

Dormant traces in rock and ice: faint grey-green veins and tea-coloured stains, easy to mistake for mineral staining.

2. Rime

Active, frost-like growth spreading through warm, wet rock, eating metals, ice and organics. A crystalline mat over translucent gel, it spreads in fern-like feathers along surfaces, seams and pipes. It gathers on heat sources such as radiators and pipework, and pulses faintly when warm.

3. Bloom

The rime fruits into intelligent individuals, the aliens proper, which build, travel and fight. They grow from swollen nodes in the rime that split open like seed pods.

4. Wane

As reserves run low, individuals settle, fold their arms in, and are slowly crusted over and drawn back into the rime.

5. Long Sleep

Dormancy until the next warm epoch: frost-furred pods fused into ice like geodes. Cut one open and it shows layered, dormant tissue.

A typical individual is two to three metres across, with no head. It has a ribbed, bell-shaped body of translucent tissue plated with frost, a dim light glowing at its core, and a cluster of branching, jointed arms like a basket star's, made for gripping and climbing in microgravity. Veils of fine sensory filaments hang between the arms.

• No eyes, no faces. They evolved in darkness, and sense heat, chemistry and vibration through their filaments.
• Stillness, then a burst. Every movement costs energy, and they behave like it.
• Warmth shows. As they warm, frost turns wet and glossy, colours deepen and their inner light brightens. Their light is a soft green, like the foxfire of glowing fungi, and used sparingly.

Minds and memory

Individuals are short-lived by human standards, but some of what they learn is stored in the rime and inherited by the next Bloom. That is why they are experts at catastrophe: they remember earlier ones. Their thinking is slow and seasonal. A conversation that matters to them may run over years.

How they see us

Waste kills: that is the first lesson of their history. To them humanity looks like a fever, a species stuck in permanent summer, running reactors day and night in a place where every joule is scarce. They believe the sane way to live is in seasons, spending in good times and sleeping through bad ones. In the belt's economy, that is a serious argument.

A Bloom is like periodical cicadas emerging: the whole population wakes at once, stocked with energy saved over a long dormancy, and spends it fast. At the peak they are overwhelming.

But a Bloom can't last. As reserves run out, the aliens weaken and withdraw, while humans, who never stop burning, keep going. When they are dormant, they are defenceless. Their deepest fear is not human weapons but a species that never sleeps, standing over them while they do.

They grow things rather than build them: reef-like structures of ice and mineral, and lattices like glass sponges.

Their vessels are grown hulls of ice and silica, moved by warming their own ice and venting the gas in jets, the way a comet does. They are slow and fragile, and in effect they are their own reaction mass: every journey spends part of the vessel, which is why the aliens travel rarely and carefully. Humans burn ice hauled from Ceres without a second thought, and to the aliens that is the fever at its worst.

The aliens are neither a hive mind nor a single people. They live in broods: separate populations, each with its own wake cycle, inherited memories and outlook. Humans number them in the order they wake, Brood I, Brood II and so on, the way periodical cicada broods are numbered on Earth.

On Hearth, broods were keyed to different tidal cycles and different parts of the ocean. A summer usually belonged to one brood, and neighbouring broods rarely woke at the same time, so their culture never had to deal with neighbours.

The shattering scattered broods across thousands of rocks, and in the belt there are no tides to time them. Each brood now wakes on local warmth, which means humans wake them unevenly, sometimes several at once. For the first time in their history, broods are sharing a summer. Alien politics is as new to them as alien contact is to humans.

Within a brood, individuals are distinct people with their own views. But they share inherited memory and wake and sleep together, so a brood decides slowly, by something like consensus, and rarely splits. Broods differ because their memories differ: each remembers different summers and different catastrophes.

Some broods' rime was damaged when Hearth was shattered. They wake with gaps in their memory, or none at all, and they wake hungry. These are the aliens no one can reason with, including other broods.

Brood I

Young and short-lived, woken early and short of reserves. Smaller and gaunt, with thin frost plating, more exposed gel, and a light that flickers unsteadily. Desperate: the first to fight humans, and the first humans ever talk to.

An elder brood

Rare, with a long cycle and the deepest memory of all. Massive and slow, with frost laid down in thick layers like tree rings, and a deep, steady glow. Cautious: it sees humans as a fever, but perhaps a useful one, and knows how to survive the Return.

A grafting brood

Has absorbed the most Earth genes from homeworld fragments, and looks it: patches of green pigment and fern-like growth inside the translucent body. Curious: fascinated by humans, and fascinating to the Seedkeepers.

A broken brood

Memory lost in the shattering. Asymmetric and malformed, with fractured frost, jagged limbs and light that is dim, absent or flaring. Hostile: it raids for reserves, and neither talks nor waits.

The frontier's greatest prize is the deep ice: large bodies of frozen Hearth ocean, pure and plentiful, enough to free a colony from Ceres's water for good, and the best reaction mass in the belt. Every frontier colony wants it.

Mining it means melting Hearth ocean inside the warmest, wettest part of a human settlement, which is exactly the condition that ends a Long Sleep. Colonies wake the aliens by succeeding.

The first fire

On Hearth, a Bloom was synchronised by the tides warming the whole ocean at once. In the belt there are no tides. The first place where the rime is woken fully and kept warm becomes the starting point, and the Bloom spreads outward from there by whatever routes it can find.

In the belt those are human routes: ice shipments, ore, cargo pods and the hulls of ships. The Waking travels along trade lines over months and years. The brood woken first becomes Brood I, and others follow as the Waking reaches their rocks.

Blame

Solar Web analysts trace the outbreak back to its source within a year or two. Ceres demands a quarantine that looks very like a blockade. The Charter Companies want samples. Some Red Clans think it's a weapon. The Scatter charges for smuggling past the quarantine. Whatever else happens, the colony that started it becomes famous for the wrong reasons.

Biomass

Organic material in a carbon-poor belt, with uses in food, materials and medicine.

Torpor

Dormancy adapted from rime biology, letting colonists or whole sections of a colony sleep through lean times on a fraction of the food, air and power.

Knowledge of the Return

The aliens have survived catastrophes like it before.

The Changed

Biomass medicine cures things human medicine can't, such as radiation damage. Some people who take it slowly drift towards something in between. It isn't mind control, just a slow biological change, and they don't see it as a loss.

Frontier colonies with rime growths had fewer air failures. The rime is neither enemy nor friend: it found human colonies useful habitat.

Hearth life and Earth life share a single origin. The aliens are distant kin, not invaders.

Earth's last wild life lives inside the rime. Burning the rime also burns the last wild Earth genomes, and the Seedkeepers split over it.

Arsia Station was given the lowest evacuation priority. It proves the Red Clans' grievance, and undermines Ceres's claim to be Earth's heir.

A Bloom should come in its own season, after reserves are built up. This one was forced early by human warmth, with the aliens short of stored energy and the Return about 75 years away. That is why they are desperate and aggressive, and why they are in a hurry to secure safe places to sleep.

To them, our Sun was the Interloper. Both species see themselves as the victims of the other's star.

The Interloper stayed by throwing away Hearth. The aliens' home was the reaction mass that brought their star to ours.

The aliens know how to survive the Return. Cooperation becomes a matter of survival, not just ethics.

Some argue that Earth life itself descends from Hearth spores, which would make humanity a feral branch of the rime. It has never been confirmed, and the argument goes on.