I'm generating a planetary classification system for a sci-fi universe. Right now I'm basing part of it off of Sudarsky's theoretical classification of gas giants (https://en.m.wikipedia.org/wiki/Sudarsky%27s_gas_giant_classification) which classifies gas giants according to the cloud composition likely to be found in a given temperature range. I plan to extend this classifications to include terrestrial planets.

Sudarsky classifies them as follows:

Class I: less than 150 K, ammonia clouds

Class II: Below 250 K, water clouds

Class III: Between 350 K and 800 K, no clouds

Class IV: above 900 K, alkali metal clouds

Class V: above 1400 K, silicate clouds.

My question is twofold:

  1. what are other compounds that can create clouds in these temperature ranges?
  2. what are some likely compositions for the atmospheres themselves at these temperature ranges?

Edit: to clarify, this is specifically for terrestrial planets with atmospheres (<4 Earth masses) rather than gas giants or gas dwarves, which I'm aware are mostly hydrogen/helium at any temperature range.


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