Prior to stardate5730, this world was established as a vital transfer point for the regular space commercial lanes. The population was counted to be one billion. The nearest starbase was Starbase 4.
In 2268, Ariannus was infected by a bacterial invasion that threatened to destroy all life on the planet. The crew of the USS Enterprise , working in tandem with the planet's ministry of health, conducted an orbital decontamination mission to save the planet's inhabitants. (TOS: "Let That Be Your Last Battlefield")