From Halopedia, the Halo wiki
The Nomos system is a planetary system consisting of the star Nomos orbited by at least two planets, including the artificial planet Genesis and its natural satellites. Serving as a Gateway to the Domain, Genesis also served as manufacturer of artificial "seed worlds".
Genesis was built in the system by the Forerunner Builders before the firing of the Halo Array in 97,445 BCE. Genesis and its system was later rediscovered in 2558 by the United Nations Space Command when the human smart AI Cortana gathered the Forerunners' Guardians at Genesis to enact her plan to enforce the Mantle of Responsibility after the remains of Mantle's Approach were transported to the planet following the New Phoenix Incident.
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