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 Advanced 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.
