Titan

The third largest populated celestial body in Sol after Earth and Mars, Titan has been an important Solar hub ever since it was first colonized in the 2150s. With its vast oceans and easily mutable atmosphere, Titan was developed over the course of the following century as the greatest and most successful example of an "eco-city" ever created. During the 22nd century, the capitol of the Saturn system was the orbiting fortress, Calliope Station, which had a population of hundreds of billions at the time of the Solar Civil War. When the war ended and half the Solar system won its independence from Earth, Titan became the most popular destination for immigration in the entire Solar system, especially from refugees leaving the old capitol, and its population skyrocketed by over 200% in just a couple short decades. Since then, the Republic has carefully continued to expand the Moon's living space while maintaining its ecological equilibrium in order to avoid the need for further atmospheric manipulation. The planetwide city laid out on the moon's surface is sometimes fondly referred to as an "eco-menopolis" on account of its combination of heavy urbanization and eco-friendly architecture. Relative to Earth, Titan has minuscule levels of poverty and there is far less disparity in standard of living between the poor and the wealthy; however, the Republic's detractors also note that it has a much more spartan way of life, where luxuries are less commonly available than they are on Earth's upper levels.