The colony was established in the 2210s to tap into the high amounts of pergium found on the planet, but also uranium, cerium, platinum, gold, and other rare ores. As Janus is not a Class M planet, the colony relied on life support systems to stay operational, which were powered by a PXK pergium reactor. The resources on Janus were so great that it was capable of supplying the mineral requirements of thousands of planets, but because of the difficulty of mining on the planet it was "only" possible to supply a dozen.
In 2267 the operation (administrated by chief engineer Vanderberg at that point) became threatened shortly after the automatic machinery opened up level 23, rich in pergium. Automatic machinery began to disintegrate, piece by piece. The metal was dissolved by an unknown corrosive agent. When a maintenance engineer attempted to make repairs, he was found seared to death by the same acid. Over the next three months, over fifty colonists were killed by the mysterious creature; only Ed Appel saw the creature and lived. Posting guards did no good; five of them were also killed (including Schmitter), and the creature's killings moved higher and higher. Production was shut down, and the planets depending on Janus VI were forced to close down their reactors.
On stardate 3196.1, the USS Enterprise arrived in answer to a distress signal from the colony. Commander Spock was able to deduce that the mysterious creature was actually a silicon-based lifeform, previously thought impossible, hence the reason it went undetected by sensors. When the lifeform stole the main circulating pump of the reactor, threatening the existence of the colony, finding the creature became imperative. Fortunately, Captain James T. Kirk succeeded in doing so, and Spock mind-melded with it, realizing it was a sentient being of a race called the Horta. The reason it had been attacking the colony was because in entering level 23, the miners had inadvertently entered the Chamber of the Ages and destroyed some of the eggs there – eggs to which this particular Horta was mother.
Kirk and Spock were able to negotiate an agreement between the miners and the Horta. The Horta agreed to return the the reactor pump, and the colonists to no longer harm the eggs. The Horta also began to assist the colonists in their mining operation, using their natural tunneling skills to locate and create access to rich deposits of minerals. As the Enterprise departed the colony, newborn Horta had already lead them to rich deposits of pergium, platinum, and gold. (TOS: "The Devil in the Dark")
The Janus VI colony was originally represented on-screen with a matte painting.