Sol

Sol is the start system that contains Earth, the world of Humanity's origin and the former seat of its power. Sol is known for its relative concentration of wealth and power due to having the oldest and most extensive infrastructure of any Solar System. Technically it boasts the highest population of any system, but most of that is on Earth and thus is not relevant.     The Terran Blockade   A network of UCH Spacy orbital platforms, assisted by long range artillery from a dedicated fleet. Its goal is to prevent any Earth-based asset from reaching or remaining in space, as well as jamming communications between Earth and the rest of the solar system. The Terran Blockade also keeps track of affairs on Earth for reporting to the Office of Terran Affairs. Technically, trade and communication with nations on Earth isn't supposed to happen but smugglers do exist (albeit with an extremely high risk involved. Landing on Earth is one thing, getting back off the planet without getting shot down is another matter entirely).   The Wheel   Previously the site governance for the United Colonies of Humankind, and previously a shipyard before that. While the seat of power and the site of the Forum has officially moved to the habitable section of Megastructure 01, important administrative offices still exist on The Wheel and it remains a key center of political power, especially in Sol.   The Red, Dead Planet   Mars is not a great place to live, but that doesn't stop a lot of people from living there. Earth was weirdly infatuated with colonizing Mars, despite the fact that they knew that colonizing the upper atmosphere of Venus was both cheaper and easier. But a lot of very useful things were learned developing Mars. It was the site of the first planetary Webb Station, acting as a shield from solar radiation in place of a natural magnetic field. It was where the Martian Strawberry was designed, where the first atmospheric generator plants were developed, and Tharsis City remains the oldest Arcology. But Mars will never be habitable outside of a sealed environment despite best efforts. And even within those environments there was no solution for the planet's low gravity, leading to numerous health complications. These days Mars serves as an large scale industrial base, making products that are not suited for zero-gravity manufacture and utilizing the planet's low gravity to ship them offworld cheaply. Mars is also a cultural center due to its close proximity to Jovian wealth, its varied assortment of experimental arcologies providing a diverse set of artificial environments, and its population. A lot of movies are shot on Mars, and martian directors have pioneered a particular kind of hyper-violent action movie known as 'bloody rust' films, which take advantage of the low gravity Martian environment for highly stylized fight choreography.   The Kings of Jupiter   During the expansion out into the solar system Jupiter served as a key industrial and economic hub due to its many moons and easily accessible resources. Corporate space ventures easily found a home in Jovian orbit early on, and that presence only grew over time. As such, near the start of Earth's seventh world war many of the rich and powerful on Earth found it convenient to make a temporary move to their Jovian real estate to wait out the conflict. A fortuitous move indeed after the colonial fleet arrived and established the Terran Blockade. These days, while the industrial element is still present the Jovian Moons have a well deserved reputation for being the home of the super-rich. You are never truely wealthy until you own a moon of jupiter. And the so called 'Kings of Jupiter' made good use of their close proximity to the seat of power. Its still said that if you hold a Wheel bureaucrat upside down and give a good shake, it will be Jovian currency that falls out of their pockets.