One of the four Galilean moons of Jupiter.
One of the most recent Sol System bodies to be terraformed. the former cold S-Class moon turned temperate E-Class has an atmosphere now stuffed with greenhouse gasses at 1.3 atmospheres and a new day of over one day, the mean temperature is a warm 23.3°C (74 °F).A heavily volcanic world, the technology to change this deadly moon into a place where humans could live was not available until the 2740s. Creating an atmosphere was the least of their worries. At the time of terraforming, Io only had around 2,000 scientists and their family living deep beneath the surface in hollowed out towns.
The terraforming began in 2752 when massive magnets were placed in orbit and miles beneath the surface of the planet. Massive drills then began to dig into the surface and were attached to massive space elevators which channeled the excess geothermal energy into the orbiting magnets and soon starships leaving the system stopped by to borrow excess energy from the moon.
Once that was accomplished an atmosphere was introduced as well as desert plants and animals, as those funding the terraforming wanted a mostly desert world. Terraforming to specifications was completed in 3131.
Despite having been terraformed millennia ago, it is the least populated of the major terraformed worlds with only 300 million inhabitants. The population is made up of mostly Arab descendants as they have adapted to the desert climates of many worlds remarkably well.
Most Ioians are nomadic, moving across the warm desert volcanic landscape most of the time. Most of the small settlements exist around the small seas that dot the world.
While the technology of the time could have made Io a relative paradise, the settlers wanted a desert environment that they were used to, so the world was seeded with desert plants and animals engineered to adapt to the environment. There is more land on the moon than water, which pools in small seas.
Despite the terraforming effort there is still a large amount of volcanism, leading the night side of the planet dotted with lava. This, in addition to the many greenhouse gasses, keeps the moon warm.