What was underneath the crust of Europa was a mystery until NASA’s Europa Clipper mission dug through the ice. What it found astonished humanity. Whether we were alone had been tentatively answered. The oceans of that world were teeming not with microscopic life but massive alien life forms. The most intelligent lifeforms on Europa were the Kya.
Missions to Europa began in earnest after this discovery. There were even proposals to terraform the moon. After a century of study it was concluded that melting the ice and giving the moon a thick warm atmosphere wouldn’t adversely affect the Europan lifeforms. In fact, many studies seemed to indicate that it would increase their living space. Terraforming began in 2170.
Slowly, the moon was warmed with focused sunlight and gases from Jupiter were imported and used in the creation of the new atmosphere. In 2272 the terraforming of the moon was completed.
The human population of Europa is 230 million, most live on floating cities above the water. The number of Kya are around 400 million.
The Europan culture is a fishing community mostly, as some Europan fish analogues are one of the most delicious meats in the Sol System.
The entire world is covered by ocean and since there is no land mass to block air currents, the winds continuously blow across the world rather predictably, and as such the storms of Europa are very predictable.
The temperature is constantly springlike.