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Small Body Group

Courtesy NASA/JPL-Caltech

Includes asteroids, planetesimals, comets and other objects smaller than a planet. They are generally not recorded on scout surveys, unless they are of particular strategic note.

The typical size for a member of this group is 10km - 30km radius, though particular types can vary (the more metallic bodies have a tendency to be smaller).

Anything with a radius more than about 400km is generally considered to be a member of the Dwarf Terrestrial Group.

Vulcanoidal Class

  • Vulcanian - These are rocky bodies in epistellar orbits, and marked by high metallic content. Rare, even unique mineralogical properties may develop because of their long term exposure (on the order of billions of years) to intense stellar radiation. First theoretically proposed by Charles Dillon Perrine in the mid-Twentieth Century.

Asteroidal Class

These are the archetypical asteroids, small and irregular bodies which are often found in specific belts or fields within a solar system, although they may also be found in eccentric solar orbits.

  • Metallic - Metal-rich, dense objects with a metallic content in excess of 50%. In most systems, these are the least common asteroidal bodies.
  • Silicaceous - Silicate-rich bodies with a silicate content in excess of 50%. These are fairly common in most solar systems.
  • Carbonaceous - Carbon-rich bodies with varying amounts of silicates and metals. They are by far the most common type of asteroid in most systems.
  • Gelidaceous - Ice-rich bodies with a frozen volatile content greater than 50%. However, unlike the Cometary Class, these bodies are in stable, relatively circular orbits which do not take them close enough to the local sun for volatile-loss.
  • Aggregate - Bodies which are essentially debris piles, held together by mutual gravity; their shapes may change over time, subtly or obviously, due to gravitational flexing. Their composition may vary, but for the most part they tend to be silicate-rich.

Cometary Class

Bodies with an ice content in excess of 50%, and which can be in orbits which carry them relatively close to their sun, causing volatile depletion and outgassing. Those that remain in stable orbits far from the star are considered passive, whilst those whose orbits taken them into the inner system are active.

Passive Type

These are Cometary bodies which remain in distant stellar orbits, or are in the slow process of having their orbits transformed into those which will take them close to the stellar primary.

  • Oort - These are dormant bodies which never venture from the outer most regions of their sun's gravity well. Typically located in the Oort cloud, these worlds are nearly unchanged from the time of their initial formation.
  • Kuiper - These are dormant bodies which never venture from their local sun's Kuiper belt, and remain relatively unchanged since the time of their initial formation.
  • Centaur - Dormant bodies which have been gravitational ejected from either the Oort cloud or the Kuiper belt, and found within the outer planetary region of the system. Their orbits are gravitationally unstable, and will likely become Active Type comets.

Active Type

These are Cometary bodies which are in orbits that take them fairly close to their stellar primary, resulting in volatile loss. These are the classical comets.

  • Brevis - Active bodies with orbits of less than 200 years Standard. They remain gravitationally bound to their stellar primary, but may still be subject to shifting orbits over hundreds of millions of years.
  • Dirunitus - Active bodies with orbits greater than 200 years Standard, and remaining gravitationally bound to the primary sun.
  • Effigia - Cometary bodies in parabolic or hyperbolic orbits; that is, they pass close to their sun (or a sun) once, and are then flung out of the solar system forever.

Damocloid Type

  • Damocloid - Cometary bodies that have lost all of their volatiles, and in appearance look quite similar to asteroids. These bodies are typically quite ancient, although some are of average age, but have been trapped within very short period orbits for most of their active lifetimes.
worldgen/pcl/small_body_group.txt · Last modified: 2019/08/22 16:50 by sam