Dust or Foreman's World was a planet on the edge of the galaxy that was colonised by the Earth Empire but never fully developed. It was eventually abandoned by the Empire, leaving the colonists to fend for themselves.
In the 38th century, Dust was visited by I.M. Foreman's Travelling Show. It was historical fact that I.M. Foreman would merge with Dust's biosphere so that they became Foreman's World. When Mother Mathara found out the time of the metamorphosis, she attempted to infect Foreman at that point with a biodata virus. This failed because the Third Doctor arrived (his timeline derailed by his future self) and died on Dust, making him vulnerable to the virus and causing him to be infected instead of Foreman. Foreman's World became a verdant, fertile planet. (PROSE: Interference)