The expanding sun warmed Europa’s open_in_new frozen surface and exposed liquid oceans beneath. Barely protected by the moon’s thin, oxygen-rich atmosphere, they began to boil off into the vacuum; as the water level dropped, submerged volcanic archipelagos began to surface.
Simultaneously, the humanity exodus raced to install magnetosphere controllers that would stabilize the thin atmosphere and shield the surface from radiation. Stabilizing the atmosphere reduced the rate of water loss, leaving the moon an ocean world studded with island chains, with a thin, breathable atmosphere.
The Jovian System
Europa is tidally locked to Jupiter, meaning that its outer hemisphere is illuminated for half of its 85-hour orbit. This creates a 42.5-hour day followed by a 42.5-hour night. The inner hemisphere experiences this to a lesser degree, as sunlight reflected off the planet illuminates it with a surreal glow.
The other Galilean moons also appear in the skies of Europa. The cadence of their orbits create a complex celestial rhythm.
Geology
Europa is highly geologically active, evidenced by frequent earthquakes and volcanic eruptions. Its many islands are coated in a thin layer of volcanic soil and demonstrate an abundance of mineral-rich hot springs and geysers.
Despite having little to no axial tilt and a corresponding lack of seasons, the massive volcanic eruptions characteristic of the moon can cause varying degrees of volcanic winter open_in_new . While life in the seas is largely insulated from these periods, they can be disruptive, even deadly, for settlers on the islands.
Oceans
Based on Europa’s high level of geologic activity, it can be surmised that hydrothermal vents are common on the seafloor. On earth, these ecosystems are highly conducive to life; on Europa, what little is known about the life the seas contain has been cobbled together from creatures glimpsed near the surface or washed ashore. Short-haul transit during colonization was handled primarily with atmospheric shuttles, and the desperate scramble for survival on the archipelago made exploration borne of simple curiosity a low priority.
Despite this relative ignorance of what the oceans may contain, their dramatic tides generated by Jupiter’s gravitational influence still permeate every aspect of life on the moon. These tides cover and expose huge swaths of land, and the sheer volume of water being moved makes them enormously fast and powerful. Meanwhile, the influence of the other Jovian moons temper or exacerbate Jupiter’s influence throughout their respective orbits. While this causes more complex tidal patterns than would be found in a simpler planetary system, with enough information they can still be predicted with a reasonably high level of accuracy.