Merrion, an icy world with numerous transparent dome-habitats
Cold Terrestrial Class worlds that form beyond the snowline of a solar system, as well as among free-floaters. They have a rocky core with an extensive icy mantle. The surfaces of these worlds are typically heavily cratered, though some may show signs of past or present geologic activity due to tidal stressing or other global factors. A few of these planets may have tenuous atmospheres due to the slow erosion of their surfaces by the weakened solar winds, or relic atmospheres formed by major geological events that occurred due to extra-planetary influences. However, the vast majority of them have no atmosphere, other than any melting due to terraformation.
Colonisation of LithicGelidian worlds
Some icy worlds acquire quite considerable populations. Deuterium in the ice can supply enough energy via fusion to warm a limited number of terraformed domes for a considerable period, and more advanced methods of energy production such as conversion reactors can heat the entire surface to above melting point. In due course the planet can become a water world, often with some rocky continents.
Even without conversion power the surface of a lithic-gelidian world can be heated using solar power, if this power could be focused sufficiently well. A swarm of weather machines or other mirrors in orbit around the planet can heat the surface; alternately a class 2 sunline or similar arrangement around the local star can collect light and direct it straight towards the frozen worlds in its system.
Icy worlds of this type are often colonised by Hiders or by the Deeper Covenant; others are colonised by factions from the major Sephirotic Empires, often in systems where the inner worlds are already populated.