GM ARKHALOS – The Rogue World Rooted in Fire – Ignis Aeternus WH 40K campaign notes

Planetary Profile

Designation: Arkhalos (Classified: Xeno-Origin World)
Classification: Rogue World / Sub-Stellar Forge-Biosphere
Orbit: None – Rogue trajectory through the void, severed from any star system
Gravity: High
Rotation Speed: Extreme (~0.5-day rotation)
Magnetosphere: Active, intense magnetic fields from molten core
Atmosphere: Layered, variable by depth — toxic in lower levels, breathable in mid-levels, nearly absent at the surface

Arkhalos does not orbit a star. It drifts through the void, sustained by intense internal heat generated by:

Tidal stress and centrifugal force due to high rotation speed
A molten, unstable core fed by near-constant tectonic friction
Massive volcanic systems, forming a geothermal biosphere independent of sunlight

Heat and vapor from volcanic lower levels rise constantly through cave vents
Steam condenses in upper levels, forming ice crystals
Perpetual avalanches and frost-fall return frozen moisture downward in cycles
This process drives a planet-wide water cycle, despite the absence of solar heating

Volcanic, acid-rich, high pressure
Constant earthquakes, geysers, and rivers of corrosive magma
Home to thermophilic microbial mats, acid-drilling wormbeasts, and lava-gliders
Extreme radiation and gravity-crushed caverns
Root network of fire-trees begins here, feeding on raw heat and minerals

Vast networks of geothermal caves and hollow lava tubes
Stable atmosphere maintained by tree-root vapors and geothermal updrafts
Rivers and lakes formed from condensed moisture
Ecosystem features:
- Blind, heat-sensitive herbivores feeding on fungal walls and root lichen
- Amphibious predator-creatures drawn to steam pools
- Symbiotic species living among tree-trunks and sap chimneys
Bioluminescence is the primary source of light

Exposed to the void, perpetually frozen, oxygen-depleted
Covered in ice dunes, ash storms, and jet-black glaciers
Scattered fire-tree buds, massive fungal-flower organisms that sprout upward and eject seed-pods into vent columns
These “flowers” provide critical nutrients and warmth for surface-dwelling scavengers and hunters
Hostile, patient predators such as shard-cats, ice-skins, and mirror-stalkers prowl these areas, adapted to silence, darkness, and waiting

(“Fire-Tree” — common term among Imperial xeno-cataloguers)

Structure:

Massive, continent-spanning organism; estimated biomass exceeds that of most ecosystems
Roots burrow into the Infernal Deep, absorbing raw minerals and heat
Trunks form the scaffolding of mid-level cave systems; many cave walls are hardened bark or fossilized vascular tubes
Buds grow at the surface, opening briefly to release explosive, superheated pollen-nuts.
Sap is acidic, bioluminescent, and pressurized—used to regulate steam flow between layers

Functions:

Regulate moisture, heat, gas, and nutrient distribution across the planet
Function as natural geothermal pumps
Serve as anchors for vertical biodiversity, with unique ecosystems at each layer of the tree’s body

This setting supports a wide range of narrative ideas, including:

An Imperial (or xenos) expedition discovers Arkhalos
Mission: extract rare isotopes from volcanic vents or study fire-tree sap as a potential bio-fuel or weapon
Threats: volatile terrain, mutations caused by prolonged exposure, the sap turning out to be semi-sentient