A mining planet whose colonists unknowingly destroy the eggs of the silicon-based Horta, provoking the attacks in The Devil in the Dark.
Janus VI is a planet where a Federation colony mines pergium and other minerals through a network of tunnels. In The Devil in the Dark the colony is besieged by a creature able to pass through rock, which kills miners and steals a vital part of the reactor.
The creature is a Horta, the last mother of a silicon-based species that lives deep within the planet. The silicon nodules the miners had been smashing are its eggs. Once the truth is known, the colonists and the Horta agree to share Janus VI, with the young Horta tunnelling for ore.