System Classification

Star systems in Known Space are typically classified according to their importance and population, and have three categories:

• Core systems - Typically have a population of over a trillion inhabitants, and represent a significant investment of a faction's resources. Typically cosmopolitan in nature, with a multitude of settlement types, and are entirely self-sufficient. Due to their importance, they also often have significant military presence, and regional governance authority. Whilst not required to be near to the Sol system, most Core systems can be found within 200 lightyears of humanity's homeworld.
• Secondary systems - Typically with a population of between 10 billion and 1 trillion, secondary systems are important to a faction, but not as much so as the bigger Core systems. Most have a cosmopolitan nature, but it is not unusual for a secondary system to focus on a specific industry or settlement type, particularly if the system has an unusual setup of planets and moons. Most secondary systems are found more distant from Sol, but not always, and tend not to have significant faction military presence, and instead rely on local defences.
• Frontier systems - With a population of under ten billion, frontier systems are not always self-sufficient, especially for those focused on mining and industry, or are stars of A or O class. Recent colonies also fall under this category, as population levels are low, even if investment and factional influence is strong. It is not unusual for frontier systems to become secondary or core systems, or conversely, to disappear entirely.

Within a system, worlds tend to be categorised according to type:

• Arid - worlds with an extremely thin atmosphere and a low water content, typically due to low temperatures concentrating volatiles into polar ice. Often with a planetary size that makes colonisation simpler, a lot of arid worlds are eventually terraformed. (Example: Mars)
  
• Asteroid - irregular shaped rocky or icy bodies often found in belts or in orbit around other worlds. Too small to possess enough gravity hold an atmosphere on its own, but when colonised, tend to be important mining or industrial stations. They can be spin up to provide suitable habitation and some are even capable of their own movement.
  
• Dwarf - bodies that are too small to be classified as planet, but are larger than asteroids and have formed into a sphere. Very similar to rocky planets (example: Pluto / Ceres)
  
• Dyson swarm - an advanced megastructure that consists of a swarm of platforms and stations entirely enclosing the inner star, usually within its habitation zone. Highly productive in terms of energy collection and industry, and can easily house trillions of inhabitants.
  
• Gas giant - a large world made up of predominantly hydrogen and helium, with a small metallic or rocky core. Often used for volatile mining, but sometimes contains primitive native life, thanks to the mix of chemicals and energies involved (example: Jupiter / Saturn)
  
• Ice - a central rocky core entirely enclosed in a shell of ice, usually water, but sometimes other substances. There is sometimes liquid underneath the ice, if the world has active geothermals, or orbits another world close enough for tidal activity to create a molten core (example: Europa / Enceladus)
  
• Ice giant - a large world made up of mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. Like gas giants, they are often exploited for their volatiles (example: Uranus / Neptune)
  
• Orbital -  a large ringed artificial structure, from a few tens of kilometers to thousands of kilometers across that rotate to provide gravity and a day/night cycle. Often with an atmosphere in an enclosed interior. Orbits the local star in a pattern similar to a planet, usually inside its habitation zone.
  
• Ring world - similar to an orbital, but entirely encircles the local star, and as such has a diameter measured in astronomical units. Vast amounts of living space for trillions of inhabitants, or has a large industrial or agricultural output
  
• Rocky - barren rocky worlds, with little to no atmosphere or surface moisture usually due to being too close, or too far from their local star. Large enough to provide Earth-like gravity, and are often terraformed over time (example: Mercury)
  
• Shellworld - an artificial structure similar in size to a planet, but has concentric levels inside, allowing for a much greater space for habitation and industry. Unlike orbitals, rings and swarms, can be built any distance from a star.
  
• Terran - a world with a hydrosphere and living biome. Sometimes naturally occurring, but usually terraformed from arid or rocky worlds. Has the greatest potential for population levels for an non-artificial world (example: Earth)
  
• Topopolis-  like a ring world, but instead of a flat ring facing inwards towards the star, is a coiled, enclosed tube, that rotates to provide gravity. Often 'braided' or looped around itself. Capable of housing incredibly large populations in a variety of environments.
  
• Toxic - a world with a thick, dense atmosphere made up of reactive chemicals, usually due to runaway greenhouse warming, or the presence of a highly active volcanic surface. Although unliveable for most lifeforms, acceptable variations of gravity and sunlight make them attractive prospects for specialised settlements. (Example: Venus)
  

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