This planet was only mentioned in dialogue.
According to the script, dated 21 June 1967, the name was written as "Alpha Proximi Two". The 26 June 1967 review of the script by de Forest Research, which adjusted for the misspelled "Proximi" as "Proxima" stated the following:
- "Alpha Proxima Two – This name does not conform with astronomical nomenclature. Suggest: Alpha Eridani Two."
Based on the episode dialog, this suggestion was followed by the script writer, however, the Star Trek Encyclopedia (3rd ed., p. 8) and a StarTrek.com entry referred to the planet by the original name "Alpha Proxima II".
A subjective interpretation of the pronunciation of the planet's spoken name in the episode, as well as the closed captioning, suggested the name "Alpha Aradoni II". The correct spelling of "Alpha Eridani II" can be found in the Redjac entry on StarTrek.com and in the Star Trek Encyclopedia (3rd ed., p. 403) as well as the Star Trek: Star Charts. According to Star Trek Encyclopedia (4th ed., vol. 1, p. 20), the planet was correctly identified as "Alpha Eridani II".
According to Star Trek: Star Charts (p. 66, "United Federation of Planets II") and Stellar Cartography: The Starfleet Reference Library ("Position of the Romulan Empire"; "Federation Historical Highlights, 2161-2385"), the Alpha Eridani (Achernar) system was located in the Beta Quadrant. This was a binary system with two B-class stars. According to a map of the Romulan Empire – prepared by the Stellar Archive Artist Lsel Essik, from the Romulan Master Data Catalog, in 2366 – Alpha Eridani (Achernar) was identified as a Romulan system.
In the Star Trek Concordance and Star Trek Maps, the original name of "Alpha Proxima II" for this planet was mentioned. According to the Star Trek Maps (p. 22), Alpha Proxima II was one of the first extra-solar Human colonies, with major industries in mining, farming, and sea-farming. By the 23rd century, the planet had a total population of 12 million with more than 3 million living in the port city Heliopolis.