Planetary Classification

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Facts

  • Planetary classification system established by mid-23rd century
  • Descends from similar classification systems established by Vulcan Science Directorate, UESPA (ENT, TOS)

Classifications

Class A

Class B

Class C

Class D

  • Terrestrial
  • Airless body, often an asteroid or moon

Class E

Class F

Class G

Class H

  • Terrestrial
  • Arid world
  • Atmosphere often saturated with heavy gasses or metallic vapors
  • Little to no surface water
  • Generally uninhabitable to humanoid life

Class I

Class J

  • Gas giant

Class K

  • Terrestrial
  • Adaptable world
  • Generally thin atmopshere
  • Little to no surface water
  • Surface conditions suitable for life with aid of pressure domes or life support technology (TOS: "I, Mudd")
    • Often pre-terraforming state

Class L

  • Terrestrial
  • Barely habitable or habitable with minimal technological aid
    • Often pre-terraforming state

Class M

  • Terrestrial
  • Previously known as Minshara-class by Vulcan Science Directorate, Earth-type by UESPA (ENT, TOS)
  • Significant surface water, below 80% coverage
  • Atmosphere consisting of nitrogen, oxygen, trace elements
  • Habitable by humanoid life
  • Subdivided into type 1-4, indicating most to least suitable for humanoid life (TNG: "The Bonding")

Class N

  • Terrestrial
  • Thick atmosphere, often saturated with sulfur compounds
  • High surface temperature due to atmospheric greenhouse effect
  • Generally uninhabitable for humanoid life

Class O

Class P

Class Q

Class R

Class S

Class T

Class Y

  • Terrestrial
  • Colloquially known as "demon"-class (VOY: "Demon")
  • Extremely high surface temperatures
  • Corrosive and/or toxic atmosphere
  • Thermionic discharges from surface-level metallic hydrogen deposits common (VOY: "Demon")
  • Planetary conditions can lead to vessel hazards even at standard orbital altitude (VOY: "Demon")

Notes

  • Star Charts classifications flawed w.r.t. giant planets
    • Radii are physically impossible
      • Jupiter diameter ~140,000km, maximum theoretical possible planetary diameter ~400,000km, but class T planets go up to 120m km?
      • Adding more mass generally tends to increase density, not radius; proximity to sun increases size but only so far
    • No acknowledgement of ice giants (not widespread distinction yet at time of writing) despite physically distinct characteristics
      • All Star charts giant classes are predominantly hydrogen-based, ice giants (i.e. Neptune, Uranus) are water/ammonia-based with very slim hydrogen envelopes
    • All gas giants listed as being in "cold zone" beyond ecosphere, which doesn't fit later discoveries
      • Written before discovery of numerous hot Jupiters by various exoplanet surveys
  • Alteration:
    • Class I ice giant
    • Class J cold gas giant
    • Class S gas dwarf
    • Class T hot gas giant (fka hot Jupiter)
      • Type I through V using Sudarsky's schema

(Star Charts unless otherwise referenced)