Io (Colony)

Io is a UNSC-controlled natural satellite and the largest moon of Jupiter and was partially terraformed though supposedly retains a harsh climate. Third largest Jovian moon. This is where the Frieden first attacked the United Nations. Despite being massively volcanic and atmospherically volatile, Io supports a large colony of Humans.

The fleet of the High Prophet of Regret passed near Io where they were detected by Io Station just minutes prior and before the Battle of Earth, allowing UNSC forces to muster a timely response.