GS391 is a planet, marginally classified as a class M world, with a size slightly smaller than that of Earth. GS391 was a temporary designation assigned by Vulcan scientists T'Clar and Spens when they identified the world as being a possible destination of the lost Vulcan starship He-shii, which had disappeared without a trace at some point centuries before the 23rd century.

The USS Enterprise arrived at GS391 investigating such a scenario, around the year 2253. The Enterprise found traces of metal from Vulcan on GS391's surface, and a landing party led by Lieutenant Spock discovered a recording from the He-shii indicating that the ship had broken up at GS391 after launching an escape pod bound for Areta. (TOS novel: Vulcan's Glory)

planets visited by the USS Enterprise (NCC-1701) (2243-2264)
Robert April's command (2243-2251) EarthRomulan planetoidTarsus IVFaramond
Christopher Pike's command (2251-2264) EarthGS391AretaMagefferus IIIPharos siteworldRigel VIITalos IVDarien 224PrairieNeyda PrimeLiriaJubalTheta KalybAlgol IITemaziCorinthia VIIEridios
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