From Halopedia, the Halo wiki
During the Great Schism, the planet was a rally point for the Sangheili seceding from the Covenant, under the leadership of Imperial Admiral Xytan 'Jar Wattinree. The Combined Fleet of Righteous Purpose met here, along with several ships from the Second Fleet of Homogeneous Clarity as well as many other Sangheili-controlled vessels. They planned to set up a meeting with the Covenant loyalists on this planet, where they would massacre the Jiralhanae and San'Shyuum leadership.
The plan failed when a NOVA bomb taken from Reach by the fleet's flagship, the supercarrier Sublime Transcendence, was accidentally detonated, vaporizing a quarter of the world, shattering the planet's moon, and destroying much of the fleet gathered there. However, due to the large size of the fleets, about a quarter of the vessels on the other side of the planet escaped. The bomb also caused massive shockwaves that leveled many cities on other parts of the planet. In addition, the explosion resulted in 300 kilometer-per-hour winds that razed many of the remaining cities, and created massive tidal waves that destroyed much of the coastline. Imperial Admiral Xytan 'Jar Wattinree was vaporized by the blast.
The Jiralhanae, knowing that Joyous Exultation would serve as an anchor point for the Sangheili forces, intended to lay siege to the planet. By the time they arrived, however, both the planet and the fleet had been destroyed.
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