Like most series, the Compact Universe has no single origin. Some of it I can trace back to a list of Star Trek tropes I wanted to avoid in the wake of the Ron Moore version of Battlestar Galactica. No transporters. Don’t name every ship after an aircraft carrier or British warship. I thought of avoiding aliens that looked a lot like humans, then decided that would make a great plot point. I’ll get to it.
I had a character back when I played in another sandbox. He was a spoiled rich kid who got sent to the military academy to straighten him out. He was an experiment, one that fit into that shared universe. I couldn’t recycle the character directly, but with some judicious reworking of the story, tweaking of the name (including giving him a surname based on my stepson), and voila. New character. And in the critical moment from the original’s backstory where he’s caught and dragged off the Shared Universe’s Academy of Cool Stuff They Do™, he instead runs away to Tian, the shining center of humanity. Well, that’s the plan. A prank sends JT Austin to Amargosa, about as far from Earth (and Tian) as you can get. It’s not even an Earth world. It’s a Mars one.
That was another idea I got. Earth and Mars being at odds. Wait a minute, you say, that’s The Expanse. Yeah, I worried about that, too, when I saw Season 1. On the other hand, the Compact Universe is interstellar in scope. The Expanse spans the solar system (and maybe a little beyond, but it’s all new there.) So that was another piece that went into the puzzle.
Finally, there is Tian itself. Its system has been visited only a little so far, but the original notes on it could be said to have spawned the series. I imagined humans locating another solar system almost identical to ours, with an extra planet inside the orbit of Hermes, the analog to Mercury. All but Tian are named for Greek versions of our own planets name with an Earth-like world where Ceres would be located. It and three other worlds are also Earth-like, and humanity swarms that system. JT’s father is a native of Demeter, the cold Ceres analog while Lucius Kray is a native of Ares, a habitable version of Mars. It even has a swampy Venus, appropriately named Aphrodite. The planet named for the goddess of love, however, has been in a near constant state of civil war for most of its history. Originally, I outlined a story of Davra as an adult having to go to there.
So the series comes from multiple sources, with more feeding into it all the time. I suspect that, once the Amargosa Trilogy is done, it will look nothing like I first envisioned. They never do.