From Halopedia, the Halo wiki
At least four (Hephestes, Barugi)
Unified Earth Government
The Tisiphone system is a planetary star system. It shares a sector with the Nereus system, Nereus being the next star Earthward from it. There are at least four planets in the system, with the fourth planet being the quarantined Barugi. The gas giant Hephestes forms a flux tube in concert with its inhabited moon, Nephis, that is a vital source of zenostium plasma.
In Greek mythology Tisiphone was one of the three Furies.