This is the only well-developed system on the Loop. It is habitable, although cold and harsh, and has a functioning biosphere of its own. The native lifeforms include a generally humanoid creature which lives in large, complex warrens underground. These creatures usually live in communities of a few dozen, although large warrens of hundreds and even thousands are sometimes found. They are not intelligent, although they use very primitive tools, such as sticks, and work together to gather food and to defend their warrens. They are fully described in Section 3.16.Aliens Adventure Game (1991), Leading Edge Games.
The population on Arcturus is approximately 25,000, but it is expanding quickly as traffic increases on the Loop and the world is adapted for human use. The leadership on the world is turning a blind eye to smuggling and other questionable activities, and has restricted Clonial Marine presence to battles with native warrens which are considered dangerous to the Colony, or which are obstacles to further expansion.