Io

Io is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3642 kilometers, the fourth-largest moon in the Solar System.

With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior by Jupiter's varying pull. Several volcanoes produce plumes of sulfur and sulfur dioxide that climb as high as 500 km (310 mi). Io's surface is also dotted with more than 100 mountains that have been uplifted by extensive compression at the base of the moon's silicate crust. Unlike most satellites in the outer Solar System (which have a thick coating of ice), Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Most of Io's surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost.

Io in "[[La Différence"
In the early 21st Century, United Europe had established several research bases on Io. A dispute over mining rights in the asteroid belt with Japan led to war with Japan striking the first blow in a surprise attack on Sengen Base.