The largest Galilean moon and the largest moon in the entire system.
The once Cold I-Class moon of Jupiter has been terraformed into a temperate O-Class world. It has a mean temperature of 15.8 °C (60.4 °F), an atmospheric pressure of 1.4 and a new day of 22 hours and 50 minutes.
Unlike Europa, Ganymede’s former subsurface oceans were lifeless, making the moon a perfect candidate for terraforming. The surface was heated and gasses were introduced by the use of captured asteroids.
Terraforming of the icy moon began in 2090, large mirrors placed in orbit to melt the ice. A thicker atmosphere was introduced with gasses from Jupiter. By 2267 the terraforming was completed.
The colonists of Ganymede brought with them many aquatic lifeforms, mostly saltwater fish and mammals and carefully introduced them into the moon’s new oceans. They took to their new ocean eagerly, spreading fast.
The capital of Jovian trade, this moon has a global population of 3.3 billion. Most Ganymedians have undergone genetic manipulation to become similar to mythical merfolk and have insisted that non-aquatic humans refer to them as such. They live in massive underground cities (the largest of which is New Atlantis), living off of the ocean lifeforms that have grown to call this moon their home.
The rest live on floating cities that spend their days fishing out of their artificial freshwater lakes and out of the ocean.
Like most oceanic worlds, its climate is very warm and predictable as there are no landmasses to block air currents.