Extra bodies, appended as given (their parent must name an earlier body).
The planet you stand on (overrides on DEFAULT_HOME). Its radius should match the World's.
The home planet's moon (overrides on DEFAULT_MOON), or null for none.
How many procedural planets to add around the star (seeded).
Seed for the procedural planets.
The central star (overrides on DEFAULT_STAR).
A star system: the star, the home planet, an optional moon, and seeded extra planets. Plain JSON.