The Expanse Wiki
The Expanse Wiki

Io is one of the moons of Jupiter and the fourth largest moon in the Sol system, slightly larger than Luna. It is the innermost of the "Galilean moons", the main group of Jupiter's moons that were discovered first.

Unlike some of Jupiter's moons, Io isn't shielded from the gas giant's massive radiation, with a standard vac suit being insufficient to protect its user. This, combined with it's tectonic instability makes it rather unsuitable for human habitation. There are numerous volcanoes across the moon that spew molten silicate into the atmosphere. Io houses research labs and supplies power cells to the Belt.


Ganymede Incident[]

Some time after the knowledge of the protomolecule was public, Mao-Kwikowski Mercantile and a covert branch of the United Nations began their secret research on how to use the "alien virus" to create human-protomolecule hybrid super soldiers. They kidnapped several children with the systemic autoimmune disorder Myers-Skelton Premature Immunosenescence, who it was easier to control the infection of, and brought them to their labs on Io.


  • Io was a maiden loved by Zeus and transformed by him into a heifer so that she might escape the jealous rage of Hera.
  • It is the most dense moon in the Sol system.
  • It is coloured yellow because of its high concentration of sulphur.
  • Io is the most volcanically active body in the Sol system.