This article is about the moon. For the ship, see UNSC Io.
Io is a moon of the planet Jupiter in the Sol system and the site of a human colony. It is the third largest Jovian moon. During the Human-Covenant War, it was orbited by at least one platform, known as Io Station.
Originally discovered in 1610 by Galileo Galilei, Io is the most geologically active object in the Solar System, with over 400 active volcanoes. Humanity began colonizing the Jovian Moons in 2080. In 2160, the Frieden first attacked the United Nations Colonial Advisers on Io, beginning the conflict which soon erupted into the Interplanetary War. Despite being massively volcanic and atmospherically volatile, Io supports a large colony of humans.
The Fleet of Sacred Consecration passed near Io where they were detected by probes from Io Station, just minutes before the Battle of Earth, allowing UNSC forces to muster a timely response. Later in the battle, the station attempted to contact John-117 onboard the Forerunner Dreadnought, passing near Jupiter. By 2558, Imbrium Machine Complex maintained the Io Design Lab on the moon for the secretive manufacture of classified MJOLNIR [GEN2] armor, such as the CYPHER-class Mjolnir.
List of appearances