So far as humanity can tell, the universe is full of habitable worlds. They’ve found them in every system they’ve been to, and settled them all. Five are what you’d call, “significant”. In alphabetic order, they are:
After Earth, Ascension was the first planet settled by humanity. The nations of Old Earth banded together to reach for the stars, and Ascension was a shining beacon of international cooperation.
At least, until the bickering started, and the colony was abandoned by its benefactors. About a generation later, Earth noticed that its child was a fractured, quarrelsome, and violent place. It needed the guiding hand of Mother Earth.
The “re-civilization” of Ascension led to interstellar war, occupation, and stalemate. Earth holds the capital and the space elevator, but not the wilds or the smaller towns.
Earth is the center of humanity, hosting 10 billion souls and supporting established centers of science and industry. Compared to the colonies, she is wealthy and mighty. Compared to her past, she is deathly ill. Monarchies became tyrannies, aristocracies gave way to oligarchies, and democracies lost their checks on the majority.
Despite the best efforts of Earth’s elites, the planet is still divided, all the old powers still hold sway. When China or the United States chooses to engage the rest of human space, the other planets jump. Fortunately for the colonies, Earth’s wealth is its own distraction — paying attention to the colonies is less rewarding than ruling Earth.
Originally “Moultrie’s World” after the billionaire that financed its colonization, Moultrie was colonized by people who wanted to be left alone. The result is a free-wheeling place, hardly recognizable as civilized by the highly-regulated Earthlings.
For their part, the Moultrons view Earth with grave suspicion. Earth’s adventures abroad have lead to “Moultrie’s Paradox”: a planet so dedicated to non-aggression is also humanity’s most militaristic. All able-bodied adults are members of Moultrie’s Militia, and their cold navy — the Volunteers — picks the ablest recruits for service. Moultrie’s most lucrative exports are spaceships and merchant crews.
They tell a story on Tzcheenucoatl of Bob Jones, a Mormon ‘naut in the early days of interstellar exploration. (A story that the Latter Day Saints on Earth label a complete lie.) Jones (so the story goes) was the sole survivor of a planetary survey gone awry. While he was repairing his spaceship (and battling hypoxia), Jones was visited by the Archangel Gabriel.
Gabriel told Jones the story of a planetary demi-urge who failed his people and subsequently went mad. Gabriel needed Jones to recruit colonists who would follow him to the mad demigod’s world, where they would battle the planet and its master to save his soul. To prove his story, Gabriel gave Jones a gold tablet that would lead him to the world.
The tablet led Jones and his followers to Sirius-B, a place where no habitable world should exist. Impossibly, they found one with the barest atmosphere: held by the higher gravity (about 1.15 Earth’s) and deep chasms, that atmosphere is thick enough in places for humans to survive.
Jones and his followers called the place Tzcheenucoatl, after the demi-urge they had traveled to save.
When space opened up to the masses, a Chinese company looked to mining other worlds, and sent survey ships to the red dwarf stars that the other colonizers were ignoring. In Xìngyùn, they found what they were looking for: a planet with a recent large-scale meteor strike. The miners weren’t interested in the meteor, but the heavy metals that it had churned up from the center of the planet.
The Big Crater on Xìngyùn turned out to be largest source of precious metals in human space. For a time, Xìngyùn carried their parent company, but the costs of space travel — plus the lackluster returns of the other planets — led the parent company to fail. Xìngyùn made its way alone after that, and the Market Revolution formalized that arrangement. While the Communists maintained control of earth-bound China, they were unable to subdue the Capitalists on Xìngyùn.
Xìngyùn currently has the highest GDP per capita of any of the planets, but its wealth is derived from providing specie for interstellar trade.