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

  • Geothermal rocky body
  • Young world not yet solidified
  • Insufficiently large to maintain atmosphere, heat following solidification
  • Primarily hydrogen-based atmosphere
  • Eventually cools to class C

Class B

  • Geomorteus rocky body
  • Orbits close to primary
  • Surface temperature high; portions of surface potentially molten
  • Little to no atmosphere due to heat and solar ablation

Class C

  • Geoinactive rocky body
  • Transition from Class A
  • Geological processes largely halted
  • Atmosphere cooled, potentially frozen

Class D

  • Airless body, often an asteroid or moon

Class E

  • Geoplastic rocky body
  • Young world not yet solidified
  • Essentially a large class A
  • Transitions to class F

Class F

  • Geometallic rocky body
  • Transition from class E
  • Surface partially solidified, geological and geothermal activity still high
  • Largely uninhabitable by humanoid life
  • Transitions to class G

Class G

  • Geocrystalline rocky body
  • Transition from class F
  • Surface essentially solidified
  • Temperatures cooling, potentially survivable range
  • Thick atmosphere
    • Often low oxygen content due to oxygen binding in crust
  • Potentially habitable with technological aid
  • Transition to class H, K-P

Class H

  • Rocky body
  • Very arid world
    • High surface temperature
  • Little to no surface water
  • Atmosphere often saturated with heavy gasses or metallic vapors
  • Generally uninhabitable to humanoid life

Class I

  • Ice giant
  • Atmospheric envelope dominated by ammonia, water, methane
    • Hydrogen levels very low (20% or lower) as compared to class J planets

Class J

  • Cold gas giant
    • Divided into three subtypes by temperature, predominant cloud formation
      • Type 1: 150K or lower, dominated by ammonia clouds
      • Type 2: 150K-250K, dominated by water vapor clouds
      • Type 3: 250K-800K, cloudless

Class K

  • Adaptable
  • 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

  • Marginal
  • Transitioned from class G
  • Barely habitable or habitable with minimal technological aid
    • Often pre-terraforming state
  • Native life often limited to flora
    • Possibly in process of transitioning to class M

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

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

Class O

  • Pelagic
  • Largely identical in composition and habitability to class M
  • Liquid water covers 80+% of surface
  • Life generally only present if sufficient landmasses to allow for mineral circulation

Class P

  • Glaciated
  • Largely identical in composition to class M
  • Surface temperatures below freezing
  • Generally covered in water ice
  • Often transitioning from prior class due to changes in available surface heat

Class Q

  • Variable
  • Previously known as Quaris-class by Vulcan Science Directorate
  • Unpredictable surface and environmental conditions
    • Generally wide variations from region to region
  • Often caused by variable star output, highly eccentric orbit

Class R

  • Rogue
  • Generally uninhabitable
    • Geothermal heat can sometimes maintain ecosystem on surface

Class S

  • Gas dwarf
  • Generally protoplanetary stage progressing towards class I

Class T

  • Hot gas giant
    • Divided into two subtypes by temperature, predominant cloud formation
      • Type 4: 900K-1400K, dominated by alkali clouds
      • Type 5: 1400+K, dominated by silicate clouds

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 4 through 5 using Sudarsky's schema

(Star Charts unless otherwise referenced)