Klondike VI was a Class J gas giant located in the Klondike system and possessing one moon, Skagway, which hosted a Federation mining colony.
In 2270, Klondike VI's rings began destabilizing, causing debris to fall on Skagway. The USS Enterprise was sent to investigate the problem and eventually determined that an alien artifact on Klondike VI allowed the rings to exist and was malfunctioning. The Enterprise was able to repair the device, restoring the rings and protecting Skagway. (TOS novel: The Rings of Time)