SUMMARY
Operation: SUNSPEAR was a mission to infiltrate Covenant space and destroy a major population center as an act of revenge for the Fall of Reach at the end of 2552. The operation was undertaken by Gray Team, who used a prowler to covertly get deep into Covenant territory. When word of the invasion of Earth and the initiation of Operation Endgame was received, Gray Team deployed a NOVA bomb onto the Sangheili colony of Glyke, home to billions of Sangheili. While the Human-Covenant War had ended in early December 2552, Gray Team had never received that message, and facing a communications blackout, proceeded with the mission. The detonation of the NOVA bomb on the surface of Glyke completely destroyed the planet, including all inhabitants. Gray Team managed to escape the destruction, but their prowler was damaged and unable to make a slipspace jump. Facing being stranded in deep space, Gray Team escaped in the prowler's escape pod, and used cryo-pods to place themselves in cryo-sleep, awaiting recovery.
RELATED MEDIA
These events are referenced in the novel Halo: Envoy, which was the subject of a Halo Book Club on April 28th, 2018.