There was a humanoid race inhabiting Halstad before it was destroyed, with pre-space flight technology. The radiation wiped out all life on the planet, even bacteria; the seas were vaporised; even the first 100 metres of bedrock were blasted to dust.
The space probes sent there said it was just a sterile desert. Bernice Summerfield said there was not much use digging there as there weren't any ruins as there wasn't any soil, and even the fossil record would have been disintegrated and was under quarantine.
Irving Braxiatel even said the whole star system was under quarantine, and the authorities thought that the radiation might not be unique. It was later discovered that it was destroyed by the Gulfrargs. The Gulfrargs destroyed it just to make its items more valued. (AUDIO: The Extinction Event)