Ariannus

Ariannus is an M-class planet located in or near Federation space and is vital as a transfer point for commercial traffic. The planet is not far from Beta Niobe. (TNG: "Conspiracy")

In 2268, Ariannus was infected by a bacterial invasion that threatened to destroy all life on the planet. The crew of the USS Enterprise conducted an orbital decontamination mission to save the planet's inhabitants. (TOS: "Let That Be Your Last Battlefield")

Timothy Sinclair visited Ariannus in the mid-2350s, and he considered relocating there after his wife's death in 2374. He bought a cabin on northern continent's coastline, where he resided while investigating ruins of an ancient civilization he believed to have originated on Sarpeidon. (Star Trek: Pendragon)