Io

Io is the innermost of the Galilean moons over Jupiter. This proximity to the gas giant leads to extreme volcanic activity. In fact, Io is the most geologically active objects in Sol System with over 500 active volcanoes. This lack of a stable surface means that the moon cannot support traditional colonies. Thanks to some innovative minds, Io has become home to the floating penal colony, Io Prime, and several ore processing facilities designed to utilize the moon's lava flows.