Gamma Arietis, also known as Mesarthim or 5 Arietis, was a star system, a trinary star located somewhere in the space of the galaxy's Alpha or Beta Quadrants.
This system was visible from Earth in the Sol system, some 164 light-years (60 parsecs) distant, in the constellation of Aries. This system was within boundaries of territory claimed by the United Federation of Planets, near the Romulan Star Empire's periphery. The Mesarthim system's orbit was the location of a number of worlds. (TOS - Rihannsu novel: Swordhunt)
The planets Vellurius, Valerian, the Mesarth species's homeworld (Mesarthim), and Starbase 20 are all located in this triple system. (TOS comic: "There's No Space Like Gnomes'!")
- Since Gamma Arietis is a "real" star system, modern scientists know a few things about its distance and makeup that were not in Star Trek.