Kastria

Kastria was a desolate planet inhabited by the Kastrians. It is possibly near the Solar system, since wreckage from the explosion of a Kastrian spacecraft landed on Earth.

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

One hundred fifty million years later, the Doctor returned Eldrad to Kastria, now a dead planet. (DW: The Hand of Fear)