Jupiter
From Halopedia, the Halo wiki
Jupiter is the largest planet in the Solar System. It was the site of various battles dating back from the Interplanetary War to the Human-Covenant War.
Interplanetary War
Jupiter represented a major battle zone during the Interplanetary War.
Jovian Moons Campaign
Main Article: Jovian Moons Campaign
During the Jovian Moons Campaign of 2160, the Frieden secessionist movement attacked the UN Colonial Advisors stationed on Io. The attack led to the Jovian Moons Campaign and the beginning of the Interplanetary War.
Human-Covenant War
During the Human-Covenant War, Jupiter was once again a location of particular importance. Io Station detected a massive Covenant fleet exiting slipspace a few moments before the First Battle of Earth.