Hyperon

This topic might have a better name.

The planet is called Hyperon not Hyperion, according to the audio, subtitles, and script of the episode.

Talk about it here.

You may wish to consult Hyperion for other, similarly-named pages.

Hyperon was a planet which sent a fleet of war rockets to intercept a Dalek invasion of Venus in the Space Year 17000, as the Fourth Doctor recounted to Davros. (TV: Genesis of the Daleks)