Janus VI was the F-class homeworld of the Horta species. It was also home to the Janus VI colony, an important Federation source of pergium. The planet was geologically inactive, and had no atmosphere. Though the planet was rich in mineral resources, reaching them was difficult with standard mining technology.
Despite the colony's establishment in the 2210s, the Federation was unaware of the Horta until 2267, when a new level was opened up and the miners inadvertently began destroying Horta eggs, causing the mother Horta to retaliate by sabotaging equipment and killing over fifty colonists by the time she was stopped three months later. Once it was realized that the Horta was a sentient creature, an agreement was created so the two sides could share the planet. (TOS: "The Devil in the Dark")