From Halopedia, the Halo wiki
The fifth planet in the system, Kamchatka, was created by the Forerunners through astroengineering to serve as a node for the Domain. Following the firing of the Halo Array, the Caspar system became a relatively obscure system on the fringes of civilization, until a Forerunner communication hub suddenly activated on Kamchatka in 2558, attracting the attention of the Unified Earth Government and Jul 'Mdama's Covenant.
Jul 'Mdama's Covenant would use Kamchatka as a staging area for the bulk of their fleet. As part of Operation: ANCHORITE, the UNSC Navy's Expeditionary Strike Group 1 launched an assault on the fleet in October 2558. The ensuring battle resulted in 'Mdama's death.