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 idea is that 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.
As described in Niven's stories, Jinx has a period of rotation of 4 Earth days long, with the East End always pointing toward Binary. 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.
Colonized in 2095. In 2097 surviving Tnuctip "whitefoods" are discovered and named "Frumious Bandersnatchi". Declared independence in 2200. In 2398 boosterspice was developed on the planet. Controlled by Kzin in the period between War One and Two.
Sources and references: World of Ptavvs, The Ethics of Madness, At the Core, Flatlander, Grendel, The Borderland of Sol, Ringworld RPG, A Gift from Earth, The Heroic Myth of Lt. Nora Argamentine, Ringworld Engineers,