“Earth is the cradle of humanity, but one cannot live in a cradle forever.” - Konstantin Tsiolkovsky
Earth, its moon colonies, and a terraformed Mars were envisioned as the seeds for humanity’s expansion into space; the first step in becoming a spacefaring species.
Positioned on a cycler trajectory open_in_new between the two planets, a pair of space stations initially established for terraforming support and later for managing transit and supply chain logistics also evolved into a population centers in their own right, before one of them was eventually appropriated by the humanity exodus for their journey to the Jovian system.