Alpha Carinae II was the inhabited second planet orbiting the primary Alpha Carinae. Classified as Class M, this was the homeworld for an intelligent species. (TOS: "The Ultimate Computer")
The planet was a conventional M class world with an oxygen-nitrogen atmosphere. On the planet's surface, there were two major landmasses and a number of islands. There were at least twenty-nine other planets that were biologically similar to Alpha Carinae II.
In the mid-23rd century, the geologist Carstairs once visited this planet while serving in the Merchant Marines on a geology survey for a mining company.
In 2268, the USS Enterprise surveyed this planet as a test of the M-5 computer's capabilities. For that test, the starship was assigned to send a general survey party to the planet's surface. The party was to avoid all contact with the indigenous lifeforms. This test was cancelled by Captain James T. Kirk after he was informed by Chief Engineer Montgomery Scott that the M-5 computer was shutting down systems across the ship. (TOS: "The Ultimate Computer")
In 2328, this planet was home to the Spaceport Alpha Carinae II. (TNG-R: "Inheritance")