Pergium is a radioactive element, frequently used in energy production by the Federation and other cultures. It has an atomic number of 111 and its most stable isotope weighs 292. Terrans discovered pergium on Mercury (Sol I) in 2023. (Star Fleet Medical Reference Manual) Pergium is rare, but has been found on various worlds, including Janus VI, Sappora VII and Timor II. (TOS: "The Devil in the Dark"; DS9: "Prodigal Daughter").
A survey of Wolf-catalogue stars within a 5-parsec sphere from Sol in the early 22nd century discovered that the fifth planet of Wolf 359 had reserves of both pergium and topaline, which led to the establishment of the Yogyakarta Baru colony. (Star Trek: Shadowstar Station)