Tarchannen system
The Tarchannen system was an uninhabited planetary system. This system consisted of a primary and at least three planets. The third planet was the homeworld for the non-sentient Tarchanne. (TNG: "Identity Crisis")
The script thrice described Tarchannen III as being a world of "perpetual twilight"; it was unclear whether this referred to the brightness of the system's sun or the planet itself being tidally-locked.