JT227 was a source of the rare isotope Promethium 62, which proved to be the Second Great and Bountiful Human Empire's salvation in the Third Dalek War.
History
Spindroids were used to mine the planet as it was radioactive, constantly guarding it from space in satellites that ringed the planet. Humanity's discovery of Promethium 62 meant that the Daleks were at last retreating from Human space, as it helped to break Dalek forcefields, forcing the Daleks out of star system out of system. However, the Daleks found the source of the element, JT227. The Daleks arrived and appeared from hyperspace in the parts of every one of the 200 satellites orbiting JT227. The Spindroids went on full alert and fought the Daleks faster and harder than Humans ever could. The Daleks only managed to breach a few of the satellites. Although their Promethium-hardened casings couldn't withstand Dalek firepower well, the Spindroids were soon able to destroy the Daleks armed with their own blasters and deadly blades. The disastrous defeat caused the Daleks to vanish from the Human front. (DWBIT: #55)