From Halopedia, the Halo wiki
The Qusdar system is a solar system in the Outer Colonies. The system is located within the Polona sector alongside Kolaqoa and Ephyra systems, in particular close proximity to Ephyra - containing the planet of Netherop.
The star hosts at least one planet; Mesra - a habitable world colonised by humanity at some point prior to 2526. In 2526, the system was invaded by the Covenant, seeking to control Mesra's xenotime deposits.