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Frigidian
Frigidian
Image from Steve Bowers
Krk, a Frigidian world in deep space. Somewhat larger than Earth, this planet has retained a thick primordial hydrogen/helium atmosphere, and is illuminated only by ambient starlight and cosmic-ray airglow
In NoLWoCS, Frigidians (prefix: Frigi-; eg. FrigiNeptunian) are the coldest of giant planets, with tropopause temperatures below approximately 30 K. Below this temperature, methane condenses out beneath the photosphere, meaning that its light absorption makes little impact on the appearance of the planet. Instead, Rayleigh scattering reflects all wavelengths back, producing the blank white appearance of these worlds. Notably, below 10-15 K, hydrogen (H2) may even begin to condense and form clouds.

At this temperature range, internal heat flux prevents all but the oldest, least massive neptunians from becoming Frigidians, and the very low irradiance required means they are always found in very distant orbits, far away from their parent stars, or as free-floating planets not bound to any star.

However, as the Universe ages, more and more planets will become Frigidians. As stars die and giant planets cool down, they will eventually become Frigidians. Eventually, hydrogen will condense into solids, overlain by a pure helium atmosphere, before it, too, condenses out.
 
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Development Notes
Text by AstroChara
Initially published on 14 October 2025.

 
 
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