This planet had a nighttime temperature that reached 120° below zero. The planet was capable of supporting life despite this, and it was also rich in a soft yellow magnetic ore with highly unusual properties.
In 2266, the USS Enterprise was on a specimen-gathering mission to this planet. While there, they brought aboard one of the dogs native to the planet. Also, Geological Technician Fisher, a member of a landing party from the ship, became covered with the yellow magnetic ore, which damaged the transporters and caused the device to divide transporter signals. (TOS: "The Enemy Within")
In 2293, the location of Alfa 177 in the Milky Way Galaxy was labeled in the star chart The Explored Galaxy, which was on display in James T. Kirk's quarters aboard the USS Enterprise-A. (Star Trek VI: The Undiscovered Country, okudagram)
This planet's name was spelled "Alfa" in script sources, on screen in the "The Explored Galaxy" star chart, and in such reference books as the Star Trek Encyclopedia (4th ed., vol. 1, p. 16) (the planet's name is given as "Alfa 117"), Star Trek Maps (p. 22), and Star Trek: The Original Series 365 (p. 043). However, The Star Trek Compendium (4th ed., p. 34) used "Alpha".
This planet was unnamed in the revised story outline of "The Enemy Within". In the final draft and revised final draft of the episode's script (dated 8 June and 9 June 1966 respectively), it was called "Reconnaissance Planet Alfa 177" and the lowest night-time surface temperature was said to be 250 degrees below zero, rather than (as it is, on-screen) 120 degrees below zero.
The surface of Alfa 177 was represented with a set built on Desilu Stage 10. (To Boldly Go: Rare Photos from the TOS Soundstage - Season One, p. 43)
For the pre-remastered version of "The Enemy Within", the brown/red planet model for Alfa 177 was first used for Delta Vega in "Where No Man Has Gone Before". It was used later for M-113 in ("The Man Trap"), Tantalus V ("Dagger of the Mind"), Planet Q ("The Conscience of the King"), Benecia ("The Conscience of the King"), Gothos ("The Squire of Gothos"), Lazarus' planet ("The Alternative Factor"), Beta III ("The Return of the Archons"), Janus VI ("The Devil in the Dark"), Organia ("Errand of Mercy"), Mudd ("I, Mudd"), Argus X ("Obsession"), and Ardana ("The Cloud Minders"). For the remastered version of "The Enemy Within", a new planet model was created by CGI artist Max Gabl.