From Halopedia, the Halo wiki
XF-063 IV-1 was the UNSC designation for the only natural satellite of the artificial planet Onyx, the fourth planet in the Zeta Doradus system. The moon was silvery in color and its surface was largely composed of ice. The cratered moon was home to numerous canyons of blue ice and methane geysers.
On November 3, 2552, Doctor Catherine Halsey whipped around the moon in the Beatrice to escape attacking Onyx Sentinels. Later in the Onyx Conflict, a UNSC battle group regrouped around the moon. Covenant ships engaged the UNSC around the moon, taking flanking positions on opposite sides of the moon. After a majority of the Covenant's vessels were destroyed by the UNSC battle group, a large Covenant fleet arrived over the moon and destroyed nearly all surviving UNSC vessels. After the battle, a large field of debris formed around the moon.
It is unknown what became of XF-063 IV-1 after Onyx was disintegrated by the planet's sentinels.
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