Zeta Doradus system
From Halopedia, the Halo wiki
The Zeta Doradus system is a planetary system near UNSC-controlled space, approximately 38 light-years from Sol. It contains many planets orbiting the star Zeta Doradus, almost all of which are uninhabitable, being icy rocky planets or gas giants. The one exception, however, is the artificial planet known as Onyx; or, after its destruction, the shield world the planet used to shelter. The system is relatively unknown to the UNSC at large.
The Zeta Doradus system was first explored in sometime around May 2491. The UNSC Engineering Corps discovered that all planets in the system were uninhabitable, except for Onyx. When massive subterranean Forerunner constructions were found on Onyx, the Office of Naval Intelligence took control of the planet. Onyx was removed from the UNSC navigational databases and the system was considered not a part of human space. ONI began to attempt to uncover the Forerunner artifacts on Onyx. The planet was also used as a training grounds for the Spartan-IIIs. The Halcyon-class light cruiser UNSC Pillar of Autumn was refit to serve in a conflict near Zeta Doradus in 2550.
In 2552, the three-sided Onyx Conflict was fought in the system between the Covenant, UNSC, and the Onyx Sentinels. All sides took massive casualties. Towards the conclusion of the battle, Onyx itself disintegrated, only leaving the shield world in its core intact. The shield world was located inside a slipspace bubble within Onyx. With the help of several Huragok, the shield world was brought back into normal space inside the system and renamed Trevelyan in 2553. When Trevelyan was brought into normal space, it enveloped the three inner planets of the system. By early 2554, the shield world had become a joint research project between the UNSC and the Swords of Sanghelios and a colony unto itself, housing a growing population of humans, Sangheili, and Unggoy.
In 2558, the Servants of the Abiding Truth landed on the shield world during the outset of the Created conflict. As a measure of protection, Sarcophagus was returned to its slipspace bubble, taking with it the three planets enveloped in its orbit. This marked the beginning of the Second Onyx conflict.
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