From Halopedia, the Halo wiki
+89 million (pre-glassing)
Unified Earth Government
Estuary was a human colony planet.
At some point during the Human-Covenant War, Covenant forces under Supreme Commander Thel 'Vadamee attacked and glassed the planet. During the battle a Punic-class supercarrier was involved at the UNSC Navy's last stand against the Covenant.