Ashkellia was an artificial planet.
It was the second planet in its system, orbiting a minor star at a distance of eighty-nine-million miles in a sparsely clustered area of Mutter's Spiral. It had an atmosphere with sulphuric acid clouds and an average surface temperature above six hundred degrees Celsius.
Ashkellia was in fact a giant particle accelerator built over a million years before the Fourth Doctor and Romana visited there. The Palace of the Old Ones was the control centre. It was used to explore the higher dimensions. (PROSE: Tomb of Valdemar)