G617 g1
From Halopedia, the Halo wiki
G617 g1, located in the G617 System, was the location of the Milky Ways first infestation by the Flood xenoform. The Forerunners first sent a Primary Pioneer Group to investigate the ecosystem of the planet. When that team disappeared, they sent the Advance Survey Team-Alpha, which also disappeared. After that, they sent a "medium intensity military exploratory detachment" to engage this new threat: this began the Flood-Forerunner War.
