Natural Satellite
A Natural Satellite is a natural body in orbit around a world.
- A Satellite World is a large satellite that has taken on socioeconomic importance, usually as a mainworld.
- They are commonly known as moons.
Description
A natural satellite, often called a moon, is an astronomical body that orbits a world. Satellites always have a lower mass than their parent world and usually have a smaller diameter.
- In rare cases a world with a small diameter and a high mass may retain a satellite with a larger diameter but a lower mass.
- Worlds and satellites with similar masses and diameters may be referred to as binary planets or Double Worlds.
A satellite and its parent world orbit a barycenter, their center of mass: this is the point around which they both orbit.
- If the parent world has substantially more mass than its satellite, the barycenter will be located within the parent world (such as Terra and Luna in the Sol system).
- If the masses of the two bodies are more equal, the barycenter will lie at some point along the line of their mean separation (such as Pluto and Charon in the Sol system).
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Background
Natural satellites tend to be the first major destination for nascent TL:4-6 sophont societies developing spaceflight.
Naming Conventions
Satellites may be individually named (such as Terra's satellite Luna), or they may simply be given a designation.
Numbers and Positions
Satellites are classified as major (created as part of the star system generation sequence) or minor (...almost always very small bodies captured by the parent world, and considered too small or insignificant to have their own separate details within the system description).
- Worlds lying within the inner system have a maximum of 1 major satellite.
- Worlds lying within the habitable zone have a maximum of 2 major satellites.
- Worlds lying within the outer system have a maximum of 3 major satellites.
- Gas giants have a maximum of 5 major satellites. They generally have many additional minor satellites.
A satellite's orbital distance from its parent world is measured in multiples of the parent world's diameter.
- Natural satellites orbiting within 70 diameters of their parent world are tidally locked to that world. Tidally locked satellites do not generally have twilight zones.
- Satellites orbiting their parent world at 70 diameters or more have their own rotation period.
Satellite orbits are identified by alphabetic letters in the following sequence:
- Ay-Bee-Cee-Dee-Ee-Eff-Gee-Aitch-Eye-Jay-Kay-Ell-Em-En-Oh-Pee-Que-Arr-Ess-Tee-Yu-Vee-Dub-Ex-Wye-Zee.
Sources
- Martin Dougherty. Referee's Handbook (Mongoose Publishing, 2021), 84.