After King Rokon proved an obstacle to Eldrad's dreams of galactic conquest, he deactivated the barriers. For this, he as sentenced to death and sent into space aboard an obliteration module. However, with the barriers down, the power available to Outer Dome Six, from where the craft was controlled, diminished. The module was detonated prematurely — at nineteen, not twenty-five spans — and Eldrad survived. With the solar winds confining them to a subterranean existence, the Kastrians, in Rokon's words, "chose final oblivion".
When the Fourth Doctor and Sarah Jane Smith visited Kastria one hundred and fifty million years later, they found that the absence of the barriers had left the planet cold and barren. (TV: The Hand of Fear)