Binf is home to about ten billion people, about 1/3 of the catacombs entire population. About 3/4 live on the planet, crowded into domes that would be cramped with half the population. The rest live in somewhat more comfort in the sprawling orbitals, or under the surface of Binf's moon. The inner orbit, nearest the star, is jammed with factories, producing anti-matter, Choi drives, and entire ships.

The planet wasn't a pleasant place when it colonized. It's cold, mean equitorial temperature is barely above freezing; the air has barely breathable levels of oxygen, and is laden with corrosive sulpher compounds. Early terraforming proceeded well. A an array of solar mirrors increased the insolation of the planet, genengineered microbes started fixing atmospheric chlorine, the partial pressure of oxygen doubled in the first two-hundred years, and a beanstalk was built.

Binf, seeing the huge volumes of traffic that were starting to pass through it, bound for other systems, decided to raise its transit fees, just a little too much. Someone released a plague that attacked the sulpher-fixing microbes; it devestated them, but would have had little long term impact, except for the civil war it caused. Twenty domes -- holding over 50 million people --, the beanstalk, and several of solar mirrors were destroyed in six days of nuclear exchanges. The orbital faction that ended up in power kept the surface subjugated, and deadly poor. Only in the last two hundred years, with the increasing supply of cheap food from Nexa have conditions on the surface improved.

One of Binf's two wormholes, leading to Nexa, is at its L4 point. The other, leading into the catacombs, is orbiting the sun in the next orbital out from Binf; average Binf-wormhole distance is just under 1 AU.