From Halopedia, the Halo wiki
Sephune was a star system formerly controlled by the Covenant.
The Sephune System was a former Covenant territory, which by late 2553 had fallen largely under the control of Jul 'Mdama's Covenant. The faction was using the third planet to gather resources for 'Mdama, something which they went to great lengths to keep secret. The planets in this system orbited the yellow star, with Sephune III falling in the system's habitable zone, and possessing the necessary characteristics to support life. The UNSC Promise of Dawn arrived in the system at some point after escaping the planet Reach, and made a hard landing on the third planet.
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