Exonium, a valuable ore capable of generating clean energy, existed in substantial quantities on the Outer Rim Territories planet of Rishi. This resource was highly prized, and the native Rishii species of the planet utilized it as food preparation fuel during the winter season on Rishi. The unique characteristics of this ore attracted settlers to Rishi, who sought to mine and trade it. Exonium's potent energy made it suitable for powering various technologies, notably the sonic weaponry employed by the insectoid Geonosian race. During the galaxy-wide conflict known as the Clone Wars between the Galactic Republic and the Confederacy of Independent Systems, the Separatist Geonosians attempted to conquer Rishi to gain control of its exonium reserves.
The current Star Wars canon first referenced exonium within De Agostini's 2022 Star Wars Encyclopedia booklet, specifically in "Mustafar and Other Planets in the Outer Rim." The concept of Exonium originated in the Star Wars Legends continuity. Its initial appearance was in The Clone Wars: The Gauntlet of Death, a 2009 comic book authored by Henry Gilroy.
- " Mustafar and Other Planets in the Outer Rim " — Star Wars Encyclopedia (Initial mention)