Definitions & Glossary

Star system types

Simply determined by number of stars in the star system:

• Single - one star total.
  • [ ✹ ]
• Binary - two stars total. Can be a close orbit binary or a wide orbit binary.
  • [ ✹✷ ]
  • [ ✹ ··· ✷ ]
• Triple - three stars total. Can be a single star with a close binary on a wide orbit, or a close binary with a single star on a wide orbit.
  • [ ✹ ··· ✷✴ ]
  • [ ✹✷ ··· ✷ ]
• Quadruple - four stars total. A close binary system having another close binary on a wide orbit.
  • [ ✹✷ ··· ✷✴ ]

Binary planets

A binary system of two planetary mass objects can be defined in two ways:

• By mass ratio: "if the mass ratio of the pair of bodies is close to 1, then the pair is a binary".
• By barycenter position: "if the barycenter of the pair of bodies lies outside both bodies, then the pair is a binary".

The first definition has been adopted in this project. A threshold dividing binary systems from planet-moon systems is set at 1:25 ratio (0.04). The ratio is chosen after the Trojan test (or Lagrange-point test).

Although, in some circumstances, the generator can create (techical) binary planets with mass ratios <1:25 (i.e., a gas giant 250 M⊕ and a super-Earth 5 M⊕, ratio is 1:50). In such cases, the adopted definition is being violated, although sometimes, the rejected barycenter definition is still being fullfilled.

Planet types

The type is determined by the planet's gaseous envelope and its composition, and the planet's total mass.

• Without gaseous envelope: Terrestrial planet (Terrestrial enum).
• With gaseous envelope:
  • Total mass <15 M⊕:
    • Ice amount in the envelope <50%: Gas dwarf (GasDwarf enum).
    • Ice amount in the envelope ≥50%: Mini-Neptune (MiniNeptune enum).
  • Total mass 15≤M<4100 M⊕:
    • Ice amount in the envelope <50%: Gas giant (GasGiant enum).
    • Ice amount in the envelope ≥50%: Ice giant (IceGiant enum).
  • Total mass ≥4100 M⊕ (≈12.9 M♃): Brown dwarf (BrownDwarf enum).

Planet classification

Definitions that can be seen in "Classification" field in a planet inspector:

By temperature

Determined by the planet's average surface temperature T:

• $\color{darkblue}\textsf{Super-cold}$:
  • T<110 K (T<-163°C). Boundary chosen after the methane's boiling point (-161.58°C).
• $\color{blue}\textsf{Cold}$:
  • 110≤T<250 K (-163≤T<-23°C). Upper boundary chosen after the freezing point of eutectic mixture of NaCl and H₂O (23.3%, -21.2°C).
• $\color{green}\textsf{Temperate}$:
  • 250≤T<370 K (-23≤T<97°C). Upper boundary chosen after the water's boiling point (100°C).
• $\color{orange}\textsf{Hot}$:
  • 370≤T<800 K (97≤T<527°C). For upper boundary see the following note.
• $\color{red}\textsf{Super-hot}$:
  • T≥800 K (T≥527°C). Boundary chosen after the Draper point: above 525°C solid materials start to glow in visible light.

By composition

• For terrestrial planets (classes can be combined):
  • Chtonian:
    • Mass≥7.5 M⊕ and SMA☉≤0.1. Assumed that if a massive (terrestrial) planet is placed very close to a star, its gaseous envelope (which normally should've been accumated) must've been stripped by violent solar radiation. Thus, "a gas dwarf/giant who lost its envelope - a chtonian planet".
  • Oceanic:
    • Ice amount in the planet's interior is ≥10%.
  • Iron:
    • Iron amount in the planet's interior is ≥60%.
  • Coreless:
    • Iron amount in the planet's interior is <1%.
• For gaseous planets:
  • Gas planet:
    • Ice amount in the envelope <40%.
  • Hybrid planet:
    • Ice amount in the envelope between 40% and 60%. Still, internall classification is binary (see planet types above).
  • Ice planet:
    • Ice amount in the envelope >60%.
• For brown dwarfs:
  • Spectral class from M7 to Y2, based on the brown dwarf's effective temperature.

By mass

Determined by planet's mass M and type.

• For terrestrial planets:
  • Asteroid:
    • M<0.0001 M⊕ (M<10^-4 M⊕)
  • Micro-Earth:
    • 0.0001≤M<0.02 M⊕. Lower boundary loosly defined after the IAU's estimate (0.5·10²¹ kg = 5·10²⁰ kg ≈ 5.97·10²⁰ kg = 10^-4 M⊕).
  • Sub-Earth:
    • 0.02≤M<0.2 M⊕
  • Earth or meso-Earth:
    • 0.2≤M<2 M⊕
  • Super-Earth:
    • 2≤M<10 M⊕
  • Mega-Earth:
    • M≥10 M⊕
• For gaseous planets:
  • For ice planets:
    • Sub-Neptune:
      • M<10 M⊕
    • Neptune:
      • 10≤M<20 M⊕
    • Super-Neptune:
      • 20≤M<90 M⊕
    • Mega-Neptune:
      • M≥90 M⊕
  • For gas planets:
    • Sub-Neptune:
      • M<10 M⊕
    • Neptune:
      • 10≤M<20 M⊕
    • Sub-Saturn:
      • 20≤M<90 M⊕
    • Jupiter:
      • 90≤M<630 M⊕ (≈ 0.3≤M<2 M♃)
    • Super-Jupiter:
      • 630≤M<4100 M⊕ (≈ 2≤M<12.9 M♃)
• For brown dwarfs:
  • Low-mass: <20650 M⊕ (≈65 M♃).
  • High-mass: ≥20650 M⊕. Chosen after the mass threshold after which a brown dwarf can burn lithium.