Europa

Europa is one of the colonized moons of Jupiter.

Geography
Like its neighbor Ganymede, Europa is a cold ice moon, with a surface made up of thick ice sheets that have a maximum thickness of 40 kilometers. It has only a trace atmosphere, primarily made up of oxygen compounds, with temperatures averaging -160oC (−260°F) at the equator and dropping to −220°C (−370°F) at the poles. The moon has unique geological activity where the ice sheet is broken up into distinctive tectonic plates, creating distinctive dark lines called linae where warmer ice spreads and cools on the surface. This process is driven by powerful gravitational interactions from Jupiter, which has resulted in Europa being tidally locked to the body. This has also led to damaging cryovolcanic activity and moonquakes, which most commonly occur on the leading face of the moon.

A subsurface ocean lies between 70 to 100 kilometers from the surface, and is heated by a combination of tidal activity and internal sources. There are some forms of native life that live here, but to the disappointment of the first colonists, these largely consist of bacteria and archaeans that are usually clustered around radioactive sources or volcanic vents. Still, this has led to the establishment of a thriving xenobiology research sector.

Though most of Europa's towns and cities are subterranean, most still reside within one kilometer from the surface due to cost and safety concerns. However, there have been attempts to establish settlements deep within its crust, and some have even reached the ocean layer. Of the hundreds of thousands of towns and cities catalogued, only a small fraction of these are actually inhabited, as Europa never recovered from the mass-exodus of the Domus Diaspora. It is only after the Human-Covenant War that the United Earth Government and Phoenix Initiative have looked into finally refurnishing these to alleviate the refugee crisis.