From Halopedia, the Halo wiki
Ephsu I Is the sole planetary body in the Ephsu system. It is a massive, uninhabited terrestrial world that has an atmosphere and water present. The planet is most noteworthy for being the anchor for Installation 07. While Zeta Halo has a history of being "different," the Forerunners typically endeavored to position the rings around gas giants so that societies would not form in the shadow of the ring and to avoid it luring in potential settlers. Rion Forge surmised that - given the circumstances in which the Halos had been dispersed and fired, the Forerunners had run out of time to find a gas giant to anchor it in a suitable firing position, or that one simply didn't exist in the sector. As of late August 2558[Note 1] Zeta Halo stood at a distance of fewer than 12,000 kilometers from the planet.
List of Appearances