(OOC Note: This page is a work in progress. Comments by experts in astrophysics or planetary geology welcome - H.)
Cyrinius is a minor planet located in Thinora System. It has a hydrocarbon atmosphere and a surface covered with hydrocarbon “ice”. It is nominally under control of the Annyrion Colonist - Eisshari Coalition, with both a planetside monitoring station and the nearby Charter Station enforcing that claim.
It is possible that Cyrinius is a gravitationally-captured rogue planet whose origins were in another system. Most planets of its size are usually found in orbit around a gas giant, in a manner similar to Titan orbiting Saturn in Sol System.
The Coalition maintains a weapons testing range in the sectors surrounding Cyrinius. Live-fire exercises are conducted regularly, and cold-weather training (requiring the use of special protective equipment) is conducted on its surface. The Coalition Shogun-class space dominance vehicle Angelus, operating out of Charter Station, makes irregularly-regular patrols of the area.