Kastria

Kastria is a desolate planet inhabited by the Kastrians, first shown in The Hand of Fear. It is somewhere near Earth, since wreckage from an explosion there made it to Earth.

At its best, it was a barren and cold, though it was constantly ravaged by stellar winds. A Kastrian named Eldrad was able to create a barrier to protect Kastria and created new silicon-based bodies to deal with the environment. These efforts were for naught though, since the barrier was destroyed and the Kastrians went extinct.