(written from a Production point of view)
According to a deleted scene from ENT: "Fight or Flight", Belarn Prime was a planet. In 2151, Ensign Travis Mayweather told Captain Jonathan Archer that the freighter Horizon once made a two light year journey from Livinius to Belarn Prime. The trip took the freighter approximately nine months.
The scene mentioning Belarn Prime is available as a deleted scene on the ENT Season 1 DVD.