The Solar System (Sol)
The Sun (Sol): The star humanity was first warmed by. There's some ancient structures still around it that we now know of as the remnants of a Dyson Sphere. Talk of fixing it up is rife in the space community to fix energy needs. The planets orbiting it are often divided in multiple 'systems'.
NEAR SOLAR SYSTEM
The areas close to Sol, it's dominated by small rocky planets.
Vulcan (Sol I). A small world that we know to be burning intensely with some of the hottest temperatures in the system. It has no night at all. People don't go there much, but the talk of precious minerals is a growing temptation...
Mercury (Sol II): Known quite derogatorily as "the planet with rocks", it was once associated with the sun before the later Greeks discovered Vulcan. Those days it's mostly a mediocre place, more or less. Just a lot of rocks. That and a fairly warm climate.
Venus (Sol III): A tropical world, the local bird-like Venutians are generally hospitable to visitors. The atmosphere is thicker than on Earth, so Earthlings may find themselves heady and dazed as they acclimate. The local human settlements seem matriarchal.
Earth (Sol IIT): Ah, home! Even as humanity terraforms other planets, there's nothing as good as home, for the time being.
Asteria (Sol IV): The home of the "counter-humans" (or the nahums, as they call themselves). They are as always, Earth's sworn rival.
Mars (Sol V): The "Red Planet", it was notably the first planet colonised by both humans and nahums. The two have reconciled recently under the principles of the Communist Manifesto. Just don't ask if the person who wrote it was Karl Marx or Rowen Obert, that'll get people shouting.
Theia (Sol VI): The "lost planet". Ancient astronomers discovered it and wrote extensively about it, but then it just... disappeared. Renaissance astronomers dismissed it as a myth, but then the broken planet parts were found in the 2020s. Project Theia, an ambitious project to rebuild Theia, is a-go!
Latona (Sol VII): Fairly recently classified as a planet by planetary standards, it's more than anything a hub for people to stop by before they go to the Middle Solar System from Earth or Asteria. Known for its gastropubs, oddly enough.
Vesta (Sol VIII): In the Asteroid Belt, Vesta stands out as the largest object, and undeniably a planet in its own right, although a 'veiled' one. It is the base of the Concord of Nations Mandate of the Asteroid Belt, established to ensure that mining in the Belt could be regulated.
MIDDLE SOLAR SYSTEM
From here to Nemesis, it's a domain of gas giants and small planetoids, with Neptune the freak exception.
Jupiter (Sol IX): The ninth planet, and the first of the Middle Solar System. It is a gas giant with many moons orbiting it. It is those such moons that are jealously seized by overzealous humans and nahums in a renewed zeal for imperialism. Have anyone asked the locals? Seems not.
Saturn (Sol X): The tenth planet, and the one with the ring everyone knows. In the ring are such moons that have increasingly become the newest clamour due to their exotic nature. I hear Britain is trying to organise a new Castreleon Conference to divide it all up. Will people listen? Especially the nahums...
Uranus (Sol XI): The eleventh planet, and I hear its moons are more sought after by companies than by governments. Something about some of their more relaxant or psychedelic atmospheres? I hear the Fair Folk are there too, though...
Neptune (Sol XII): A water planet that staggered people with its size. It holds the majority of water in the entire system. The Calamari are originally Neptunians, and we're trying to find their relatives there. But the British Further Stellar Company is pushing for the Company to own Neptune...
Orcus (Sol XIII): As the first gas giants pass us by, we approach the realm of the midgets. Orcus is by far the most fabled of the further planets, with many orcs going back into prehistory talking of a place among the stars just for them, and it was named by an orc astronomer. Orc settlement is growing.
Pluto (Sol XIIT): The theteenth planet, it is by far a British possession and home of the British Further Stellar Company. The local Plutoids, a bunch of cheerful bespectacled yellow-skinned... things, seem to be happy enough with it. In fact, they want to be, in their own word, 'minions' to the Empire.
Haumea (Sol XIV): Loosely claimed by Canada and Australia, the two often squabble over who has the rightful claim. Really, it's this far that control becomes theoretical. The British control of Pluto is because of the Plutoids' strange enthusiasm, and apart from that control breaks down after Neptune.
Quaoar (Sol XV): Loosely claimed by France and Germany. The place is known for being cold.
Makemake (Sol XVI): A bunch of competing claims here because it's known as an "oasis planet", with the geology regularly keeping it warm.
Gonggong (Sol XVII): The many competing claims here are all from the countries that claim to be China. And their Asteria equivalent Nachi. Yes.
Eris (Sol XVIII): Often debated on if it's a planet with many moons or a collection of asteroids, it's nevertheless claimed by Tawantinsuyu.
Sedna (Sol XIX): The furthest
reliable planet in the Main Solar System, and claimed by Magnallem, aka Counter-Germany, since a couple of years ago.
Veritas (Sol XX): This planet has for time and time eluded humanity and nahumity, with countless discoveries made naught by disappearance. It has gone by many names, but the one that humanity and nahumity uses now is the name of the elusive Roman goddess of truth.
FURTHER SOLAR SYSTEM
At this point it's more accurately called the Nemesial System, but Nemesis revolves the Sun, so this is still part of the wider System
Nemesis (Sol XXI?): A sun? Seems like it, but the arguments between sun and planet is rife. The current consensus is sun, but there's plenty of historical textbooks that call it a planet or a sun-planet (such a category does not exist in science). It lacks any Dyson Sphere remnants like Sol.
Diana (Nemesis I (Sol XXI/XXII?)): The first planet orbiting Nemesis, it is a very hot planet, often labelled the second Vulcan.
Arrakis (Nemesis II (Sol XXII/XXIII?)): The second planet orbiting Nemesis, it is a quite dry planet, from what people can work out about it. Apparently peopled by a primitive insect civilisation (the Arrakes), from what we know from the GU.
Kamino (Nemesis III (Sol XXIII/XXIIT?)): The third planet orbiting Nemesis, it appears to be a water-dominated planet that the Galactic Union says has sapient life called the Kaminoans. This is the first planet that neither humanity nor nahumity discovered, but was informed by the galactic government.
Demeter (Nemesis IIT (Sol XXIIT/XXIV?)): The thetath planet orbiting Nemesis, it is noted as a very fertile planet with zero sapient life, and is by far the planet humans and nahums are eager to get to. There's currently a ship heading there now from Earth, and Asteria is prepping theirs too.
Calliope (Nemesis IV (Sol XXIV/XXV?)): The fourth planet orbiting Nemesis. A more temperate planet compared to the undying abundance of Demeter, it is nevertheless one that has become the most popular one in pop culture and the arts, mostly as a distant love. The Merfolk love this planet.
Ambrosia (Nemesis V (Sol XXV/XXVI?)): The strangest planet in the entire Solar System by far, this fifth planet of Nemesis has been described in many ways, "decored", "holed", even "an abomination to God and men". What we know is that it is a toroid planet, a 'donut' one if you will.
Asteroid Belt: Unlike the Main Solar System, this one has no planets known of.
Guanyin (Nemesis VI (Sol XXVI/XXVII?): The sixth planet is a gas giant, but one with plentiful moons, each known to be strangely habitable even this far from Nemesis. The Galactic Union often notes that the people of Kamino and Arrakis often consider Guanyin to be a 'calming presence'.
Tartarus (Nemesis VII (Sol XXVII/XXVIII?): The final planet in the solar system is a dark one, filled with storms and thick clouds preventing light from reaching the geologically-destructive surface. It is not a planet to visit, that's for sure.
The generally accepted number of planets with most people is
30. You exempt Nemesis for it is a sun, and you don't acknowledge the secret number of theta prime, for it is only known by GDI and various interlopers. Earth is known as the fourth planet by normal people.