The fifth zone is an unusual formation of debris surrounding the super heavy core of a planet that failed to properly form.
The core of the unformed planet spins and generates enough of a gravitational pull that it keeps the debris and space dust from escaping. This core is surrounded by a thick accretion disk of proto planetary material.
The Z5 Crucible-G Outpost is actually anchored to the core with a space elevator on one of the poles, providing direct supply and personnel movement to and from the outpost to the core.
The accretion disc offers opportunities to access materials usually buried deep within a planetary body. This is accomplished by both automated mining drones and manned mining shuttles.