Rigel Seven

Rigel Seven was a planet with plenty of rich fertile soil and a heavy rainfall; this climate caused an abundance of mud, which was appreciated by its inhabitants, the Rigellans.

An incarnation of the Doctor visited it and muscled in a political crisis. Years later, the Sixth Doctor came back with Peri Brown. (PROSE: Players)

In 2620, there was an Earth Empire colony on the planet. (AUDIO: Singularity)

Behind the scenes
Perhaps coincidentally, the aliens Kang and Kodos from The Simpsons originate from Rigel 7.