Planetary shields were a variant of Forerunnerenergy shielding technology that could be extended to cover entire planets to protect from stellar radiation. Sections of a planetary shield could be temporarily lowered to allow starships to pass through. Normally, a planetary shield was barely visible, but caused noticeable refraction when opening or during sunset. The homeworld of Bornstellar Makes Eternal Lasting was protected by a planetary shield.
^Halo: Cryptum, page 254: "A streak shot across our sky, and our planet's protective shields opened a glittering gate, like a ring of precious stones, through which that streak now passed, slows, turned upright..."