Sigma Niobe II was a planet in or near Federation space in the 23rd century. It was class M, though with a significantly denser atmosphere than that of Earth.
History and specifics[]
Sigma Niobe II was home to a humanoid race referred to by Federation observers as Niobeans. The dominant subgroup were the Yemai, who belong to the Yemai Empire; there were also smaller subgroups, such as the Ilaiyenai of the Ilaiyen Archipelago. (TOS - Constellations short story: "As Others See Us")