Krysto
The ice planet.
A frozen moon of a gas giant around Alpha Centauri A, and the fuel depot of settled space. Humanity's first interstellar settlement.
- Star
- Alpha Centauri A
- Gravity
- 1.0 g
- Population
- A few thousand, mostly on rotation
- Breathable
- No: sealed suits needed
Statistics
| Where it is | |
|---|---|
| Star | Alpha Centauri A |
| Designation | Moon of Alpha Centauri Ab |
| Star type | G2V, almost identical to the Sun (1.5× as bright) |
| Distance from Sol | 4.37 ly |
| Orbit | ~1.2 million km from the gas giant Alpha Centauri Ab, which circles the star at ~2.0 AU (1.2–2.8 AU, eccentricity ~0.4) |
| Year | ~2.7 years (the giant's orbit) |
| Day | ~15.5 Earth days (tidally locked to the giant) |
| Real-world status | The giant is a real candidate (imaged by JWST); Krysto is invented |
| Size | |
| Type | Captured ice moon of a gas giant |
| Radius | ~1.2 Earth radii |
| Mass | ~1.5 Earth masses |
| Density | ~4.5 g/cm³ |
| Surface gravity (g) | 1.0 |
| Environment | |
| Atmosphere | Thin nitrogen with some CO₂ |
| Breathable | No: sealed suits needed |
| Temperature | Averages about −50 °C; −10 °C in the Thaw, below −100 °C in the Long Dark |
| Surface | A thick shell of ice over rock, with a salty ocean beneath |
| History | |
| First explored | ~2039 (first crewed survey of Alpha Centauri) |
| Colonised | ~2041 (mining outposts) |
| People | |
| Population (2076) | A few thousand, mostly on rotation |
| Role | Fuel depot of settled space |
The star and the giant
Krysto's parent planet is a Saturn-mass gas giant, Alpha Centauri Ab. In the real world this is the candidate JWST imaged in 2024, which fits an eccentric orbit around Alpha Centauri A between about 1 and 2 AU. In-universe it has long since been confirmed.
Krysto is tidally locked, so the giant hangs fixed in the sky of the near hemisphere, about 14 times the width of the full Moon. Its seasons follow the giant's eccentric orbit:
- The Thaw (near closest approach to the star): equatorial highs around −10 °C, with brief meltwater slush in sheltered basins.
- The Long Dark (at the far end of the orbit): temperatures drop below −100 °C.
Why it stays frozen
Krysto receives enough starlight on average that a darker world might thaw. But its bright ice reflects most of that light away, so it stays locked in a permanent "snowball" state. The same effect is thought to have frozen early Earth solid for millions of years.
Resources: why the fuel is here
- Deuterium-rich ice. Krysto formed far out in the cold of its system and was later captured by the giant. Ice from cold regions is enriched in deuterium, as comets are in our own system. Krysto's ice holds two to three times the deuterium of Earth's oceans.
- Lithium brines. Beneath the ice, a salty ocean has concentrated lithium into brines. Lithium is the raw material for breeding tritium.
- Helium-3 is skimmed from the giant's atmosphere by orbital scoop stations.
- Frozen mineral wealth: salts, clathrates, and metals in the rocky crust.
Together these make Krysto the fuel depot of settled space. Its refineries breed tritium for the small deuterium–tritium ships that depend on it, and supply deuterium and helium-3 to everyone else.
Settlement
Krysto was the first world substantially explored and settled by humans (~2041), because its surface was survivable with suits and it was only a few days from Earth. It has never supported a large population. People live in isolated mining outposts dug into the ice, orbital refinery stations, and scoop platforms around the giant. The culture is industrial, practical and tight-knit, with company towns and old-timers who remember the first landings.
Hazards
- The giant's radiation belts bathe the surface, so outposts are buried in the ice.
- Crevasses and ice quakes, driven by tidal flexing from the giant.
- The cold, especially during the Long Dark.