Io, the first moon of Jupiter, was the last place visited by The Traveler, and the site of great interest to both humanity and the timeless Vex machines. The Red Legion, too, now seek to unravel the secrets and power of this place, gouging at the surface, seeking to uncover new sources of power to aid in their quest to dominate our worlds. It is up to us to protect this place, and preserve its great legacy. In the final days of the Golden Age the Traveler was in the midst of terraforming Io when it detected the Darkness approaching and abandoned the moon as it fled to Earth. As a result of this, the Ionian climate and geography do not support traditional agriculture, meaning that some remnant of Io’s original atmospheric composition prevented the full growth of plants. Echo Mesa, a mountain on Io, has become a popular pilgrimage site for Guardians, and considered sacred to warlocks due to it overlooking the Mesa, a crater where the Traveler left behind a mysterious city-like structure.

During the the Red War, Io became a warzone for Guardian, Red Legion, Vex and Taken forces. Io was the final place that the Traveler influenced with Light in the Solar System, and as such is sacred ground to Warlocks. During the conflict, Zavala orderd me to search for Ikora there, as she off all people would have fled there after lousing her light. After locating her, she sent me on several missions into a Cabal research base, ultimately revealing the Red Legion’s plans for the Traveler and the Light. The Cabal were mining out the remaining Light energy from the Traveler, which attracted the forces of the Taken and forced the Cabal to evacuate. During the my time on Io, I also meet yet another famous warlock, Asher Mir, an Awoken scientist fixated on the Vex, along with their activities on the planet.

A Vex structure known as the Pyramidion is found there, which was fought over by the Taken in another attempt to infect the Vex like Oryx had with the Vault of Glass. The exact purpose of the Pyramidion is unknown, but it is believed to be merely one of many entry points into Vex space, where one of their Axis Minds performed experiments on captured Guardians.
A hidden Warmind vault, JYS-2, was buried beneath Io’s surface and inadvertently uncovered by one of the Cabal’s drills. An active AI was still using the facility but did not identify itself. Instead, it communicated via pre-Golden Age music and philosophical quotations, which proved to intrigue both the Vex and myself.