It is one of the oldest, most populous human colony worlds.
The world is a satellite of a gas giant named Binary in the Sirius A system, and is home to a human colony. Jinx is six times more massive than Earth, and very dense, with a surface gravity of about 1.78 times Earth gravity. Its nickel-iron core is half the diameter of the world, the rest being rocky mantle and crust. Its most distinctive feature is its shape, that of a prolate spheroid (a rugby-ball or egg-shape). The shape of Jinx was fixed when it was in a close orbit to its primary, leading to tidal forces strong enough to produce this shape. Over time, tidal effects have caused Jinx to recede from its primary, while at the same time the planet has cooled and become more rigid, retaining its distorted shape. The extreme variations in altitude caused by this unusual shape have resulted in five distinct environmental zones.
Along the meridian, where the atmosphere is thickest, runs a narrow band of high-pressure not suitable for human habitation. On either side of the meridian are two zones or bands where the atmosphere is suitable for human habitation. These are known as the East Band (home to the well developed colony), and the West Band (still a developing frontier). The "tips" of the spheroid are the East End and West End, which stick out of the planet's atmosphere into the vacuum of space. This makes the ends uninhabitable, but excellent for vacuum industries.
In order for the crust to vary in altitude relative to the ocean and the atmosphere, the body has to be rigid enough to retain its shape under its own gravity. Jinx has a distinct lack of radioactive materials, so that the it would cool more quickly and become more rigid. There are also frequent earthquakes as Jinx' own gravity tries to draw it into hydrostatic equilibrium, in which the force of gravity is normal to the surface at every point. It is not clear whether rock could actually be rigid enough to retain such a deviation from equilibrium over geologic time scales.
Jinx has a period of rotation of 4 Earth days long, with the East End always pointing toward Binary.
The poles lie in vacuum, the equatorial regions are Venus-like (and inhabited by the Bandersnatchi); the zones between have atmosphere breathable by humans. Jinx's poles become a major in vacuo manufacturing area
The Capitol and seat of Jinxian Government is located in the East Band city known as Sirius Mater.
Jinx is home to the Institute of Knowledge , one of the most advanced research facilities in Known Space, which also contains a comprehensive museum. The Institute is located in Sirius Mater. Most offworld visitors to Jinx stay at the Camelot Hotel adjacent to the Institute, as there is gravity control in the guest rooms. The bar and event halls in the Camelot are maintained at one Earth gravity throughout the facility.
Jinx is home to an intelligent race known as Bandersnatchi. Bandersnatchi were created by the Tnuctipun when the planet belonged to the Thrint Empire. They inhabit the shores of Jinx's major body of water, a ring-shaped sea that runs along the meridian. The species is adapted to live in this high-pressure environment. At one time the sole intelligent inhabitants of Jinx, the Bandersnatchi have allowed humans to settle the planet, and have exchanged hunting rights for themselves (a most risky endeavor, as one human usually dies for every bandersnatch killed) in exchange for technology.
Due to the high gravity, the human inhabitants of Jinx have short, squat bodies with great strength (and a predisposition to heart failure). As Julian Forward says: "We bred for strength, we Jinxians. At what cost to other factors? Our lives are short, even with the aid of boosterspice. Longer if we can live outside Jinx's gravity."
They also tend to have very dark skin because of the intense sunlight of Sirius. Jinxian architecture is similarly shaped, with short, squat buildings so as to not collapse under their own weight. Jinxians are also known for their proclivity toward puns.