Pluto

Pluto is a dwarf planet (previously classified as a planet) in the Sol system. It lies between Neptune and Eris. It is the same classification as Ceres and Eris.

The planet which was also known as Sol IX became Humanity's new home after Earth's resources were exhausted. These remaining Humans were shipped to Pluto by the Usurians, and 6 artificial suns were placed around Pluto. (DW: The Sun Makers)

Behind the scenes
At the time that The Sun Makers was produced in the late 1970s, Pluto was officially classified as the solar systems ninth planet. Its subsequent demotion in 2006 is one of the most controversial decisions in modern astronomical history, and is expected to be challenged in coming years. It is possible, therefore that in the future it may regain its planetary classification.