Beneath Io’s tenuous, patchy atmosphere of volcanic gases and neutral atomic dust lies a barren, grayish yellow, rocky surface coated with a thin frost of sulfur dioxide. Tidal heating caused by gravitational interaction with Jupiter makes Io the most volcanically active body in the system—so active that the meteor cratering found on every other planet and moon is completely absent on Io. Massive volcanic calderas, lakes of molten rock, and geysers of sulfur dot the surface, with eruptions and accompanying seismic activity lasting months or years. Volcanic zones on Io reach surface temperatures of up to 1,500 Kelvin, hotter than any body in the system.

For all that, transhumanity’s worst peril on Io is radiation. Ejecta from geysers and volcanoes ow with Jupiter’s magnetic eld to form a titanic, toroidal ux tube that rotates with Io around the gas giant. Travelers to Io must either use the heaviest radiation shielding available or resleeve into synthetic morphs.

Transhuman activity on Io centers around scientific research and harvesting the volatiles ejected by Io’s geysers, particularly sulfur. Bases tend to be modular and mobile due to the ever-changing seismic activity. The Junta’s most notorious prison, Maui Patera Rehabilitation Center, is dug into a (mostly) extinct caldera wall north of the equator.