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Ymirian Worlds

Worlds made almost entirely of ices

Selenian
Image from Steve Bowers
Sheol

Formerly know as Glacian Type Worlds.

Planets and planetoids found in the most distant parts of the solar system, almost completely composed of ices, generally with little or no atmosphere. Smaller objects of this type are known as Kuiperian type worlds. The most common ices are water ice, ammonia ice, and on extremely cold worlds, layers of nitrogen ice and carbon monoxide ice may be present.These worlds have either a very small or an entirely absent rocky core.

Typically there is no atmosphere, as nearly all gases found at these temperatures freeze out onto the surface. However tidal interactions with the primary world, or with moons if present, may lead to outgassing in the form of cryovolcanoes. Note that around 5% of all Ymirian worlds have their own satellite(s), while a significant fraction of all such worlds are found orbiting larger worlds.

Utmig
Image from Steve Bowers
Utmig's ring system, a relatively transient feature
Their surfaces are highly reflective, although some are decidedly reddish in color due to organic material interacting with solar and cosmic rays. Heavily cratered, the geologic activity on these planets is almost entirely restricted to primordial times, but may leave surface features visible for billions of years. What little rocky material that does form with these worlds goes to form a small and non-molten core.

See also Ymirian in the Extended World Classification System.

Examples: Sheol, Cynthia, Aminon, Utmig
 
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Development Notes
Text by John M. Dollan
Initially published on 18 November 2008.

 
 
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