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Star Trek Planet Classification

lpetrich

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Star Trek has a planet-classification system that was likely inspired by the spectral-type system of stars: OBAFGKM. From several sources, one can piece it together. Planetary classification | Memory Alpha | FANDOM powered by Wikia, Ex Astris Scientia - Planet Classification,  Star Trek planet classification

  • A: Gothos
  • B: Mercury
  • C: Pluto
  • D: Small airless rocky planetoid: Earth's Moon
  • E, F, G: proto-Earth-sized
  • H: Earth-sized with an arid surface
  • I: Gas supergiant, larger than J
  • J: Gas giant: Jupiter, Saturn
  • K: Earth-sized, cold: Mars, Mudd
  • L: Earth-sized, marginally habitable: several
  • M: Earth-sized, habitable for humanity: Earth, numerous others
  • N: Earth-sized, hot: Venus
  • O: Covered with water
  • P: Covered with water-ice
  • Q: Very changeable due to an eccentric orbit or star variability
  • R: Rogue planet (one that orbits no star)
  • S: Gas ultragiant, larger than I
  • T: Gas ultragiant, larger than S
  • Y: a "demon" planet, one with very nasty surface conditions
  • X, Z: other "demon" planets
Before about 500 million years ago, the Earth itself was pretty much class L, because of its low atmospheric-oxygen levels (about 10% - 20% present-day in the mid-Proterozoic, and essentially 0% in the Archean and Hadean).

[0707.2895] Mass-Radius Relationships for Solid Exoplanets has some calculated-structure curves in its Figure 4. The largest sizes are reached for masses around 1000 Earth masses (3 Jupiter masses). H-He: 11 Earth radii, water: 5 Re, rock (MgSiO3): 3.5 Re, iron: 2.7 Re. Jupiter is about as as big as a planet can get without something puffing it up. So J is as big as it gets, and I, S, and T are not physically possible without some artificial puffing up. But if "size" refers to mass, then I, S, and T are possible, even if smaller in space dimensions than J. They could fade off into brown dwarf stars.

One of the sources is Mandel, Geoffrey (2002). Star Trek Star Charts: The Complete Atlas of Star Trek, and that is of doubtful canonicity.
 

Sarpedon

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Can we have a non-star trek reference for Class A? Isn't Ceres Class A?
 

Loren Pechtel

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Note that class M planets inherently have substantial native life. You can't have oxygen in the atmosphere otherwise.
 
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