Planetary Classes

According to the Universal Cartographic Union, a planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium, and (b) does not undergo self-sustaining fusion or naturally emit light at any point in its life cycle. This definition is broad enough to include moons and brown dwarfs, though the definition's stipulations require these two types of objects to be specified by name.

The planetary class designations of planets and moons are composed of numbers and symbols representing particular defining aspects of themselves, arranged categorically. These lengthy but thorough class designations are intended to convey to the reader, in short and simple alphanumeric series, a very general but fairly accurate assessment of what the planet is like.

Universal Class Categories

Size

All planets can be classified as one of the following basic size classes based on their average radius:
  • Substellar (radius of 64,000 km to 96,000 km)
  • Giant (radius of 32,000 km to 64,000 km)
  • Large (radius of 12,000 to 32,000 km)
  • Medium (radius of 4,000 to 12,000 km)
  • Small (radius of 1,000 km to 4,000 km)
  • Dwarf (radius of 1,000 km or less)

Temperature

All planets and moons can be classified as one of the following temperature classes based on their average surface temperature:
  • -3 = Ultracold (-101°C and below)
  • -2 = Frigid (-100°C to -50°C)
  • -1 = Cold (-50°C to 0°C)
  • 0 = Temperate (1°C to 50°C)
  • +1 = Hot (51°C to 100°C)
  • +2 = Scorched (101°C to 150°C)
  • +3 = Hyperthermal (151°C and above)

Atmosphere

All planets and moons can be classified as one of the following atmospheric classes based on their atmosphere's extent from the surface:
  • 0 = Null Atmosphere (0 to 2 km)
  • 1 = Thin Atmosphere (3 to 10 km)
  • 2 = Moderate Atmosphere (11 to 20 km)
  • 3 = Heavy Atmosphere (21 to 30 km)
  • 4 = Superheavy Atmosphere (31 to 40 km)
  • 5 = Crushing Atmosphere (41 km and up)
  • G = Gaseous (composed entirely of atmosphere)*

*G-class planets diverge in their classification from the atmosphere subsection onwards. See the later section on subclassifying G-class planets.

Terrestrial Planet Class Categories

Solvent Presence

All terrestrial planets and moons can be classified as one of the following solvent classes based on the percent of liquid solvent present on their surface:
  • 0 = Barren (0%-10% of the planet's surface is occupied by liquid solvent)
  • 1 = Arid (11%-25% of the planet's surface is occupied by liquid solvent)
  • 2 = Semiarid (26%-40% of the planet's surface is occupied by liquid solvent)
  • 3 = Balanced (41%-60% of the planet's surface is occupied by liquid solvent)
  • 4 = Saturated (61%-75% of the planet's surface is occupied by liquid solvent)
  • O = Oceanic (76%-100% of the planet's surface is occupied by liquid solvent)

Terrain Type

All terrestrial planets and moons can be classified as one of the following geological classes based on the terrain that comprises the highest percent of (non-solvent) surface area:
  • C = Cryonic (51% or more of surface is ice)
  • S = Selenic (51% or more of surface is "dead" rock)
  • T = Terrestrial (51% or more of surface is "living" rock)
  • V = Cthonic (51% or more of surface is volcanic)
  • M = Metropolic (51% or more of surface is urbanized)

Biosphere Classification System

A planet's biosphere is a classification system of its own. Its class designation is determined by a number of factors, including its biochemical basis.

Biotic Dichotomy

All planets and moons can be classified in this category as either 0 (indicating life is not present), or a positive integer indicating the atomic number of the indigenous life's base element. The most common biotic designations are:
  • 6 (hexaprotium-based life)
  • 7 (heptaprotium-based life)
  • 14 (quadecaprotium-based life)
  • 5 (quinprotium-based life)
  • 15 (quindecaprotium-based life)
  • 33 (triterticontaprotium-based life)
  • 82 (dioctocontaprotium-based life)
  • CN (chemically indiscriminate life)

Base Energy

Biospheres are also classified according to the dominant form of autotrophic/metabolic energy synthesis, of which there are numerous kinds:
  • Φ = Photosynthetic
  • Ω = Photovoltaic
  • Ε = Electrosynthetic
  • Θ = Thermosynthetic
  • Ξ = Chemosynthetic
  • Γ = Nucleovoltaic
  • Δ = Nondominant/Indiscriminate

Planetary class designations can be revised by the Universal Cartographic Union every 25 cycles or as necessary, and biosphere class designations can be revised by the Council of Planetary Ecological Management every cycle or as necessary.


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