From Halopedia, the Halo wiki
During the Human-Covenant War, Ealen IV was considered a valued prize by the Covenant due to its proximity to the Outer Colonies, and the planet was later terraformed solely for the purpose of producing plasma for large-scale industrial work. The Covenant established many defensive redoubts on the planet which were later decommissioned. Ealen IV features a unique weather phenomenon known as a plasma storm which is characterized by constant electrostatic discharges unto the surface of the planet. In addition, the planet's atmosphere is known to cause communication interference.
Battle of Ealen IV
In March 2558, the planet was the site of peace negotiations between Fleet Admiral Terrence Hood, Thel 'Vadam, and Jiralhanae Chieftain Lydus. During the negotiations, the group was attacked by Covenant mercenaries led by Vata 'Gajat, resulting in the Battle of Ealen IV.
The group proceeded to fight their way to the redoubt on the planet, where they discovered that Spartan Vladimir Scruggs had betrayed them and was working with the Covenant. The rogue Spartan took Admiral Hood hostage, but Spartan Sarah Palmer was able to kill Scruggs before any harm could be done to the delegates. Captain Thomas Lasky contacted the fleets and asked them to cease their infighting and send their forces to the delegates' aid instead. However, both sides refused to listen to him while a massive Covenant force converged on the redoubt. Eventually, the group found a Covenant cargo tug in the redoubt and used it to escape, while Spartan Fireteam Bailey and Paul DeMarco sacrificed themselves to cover the group's escape.
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