Chaltok IV

Fourth planet of the Chaltok System, Chaltok IV is located inside the territory of the Romulan Star Empire. A research facility was constructed on the planet during the 2260s. The primary research involved potential uses for polaric ion energy. The facility was destroyed in 2285 by an immense explosion, convincing the Romulans to sign the Polaric Test Ban Treaty. (Voyager: "Time and Again")

The resulting polaric radiation contamination made the planet uninhabitable, and the Romulans have so far ignored trying to clean up the mess. Instead, they placed another research facility in orbit around the planet at the dawn of the 24th Century. According to Starfleet Intelligence, it is one of the key locations for the Romulan's continued transwarp research.