Hyperon

Hyperon, also known as Hyperion, (PROSE: Doctor Who and the Genesis of the Daleks) 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)

Behind the scenes
For the charity stage play The Trial of Davros in 2005, a sequence called "space year" was shot depicting Hyperon intervention against the Daleks with Jeremy Bulloch portraying Chairman Skellon.