Ceres

Ceres was a dwarf planet in the Sol system, located in the asteroid belt between Mars and Jupiter. (AUDIO: The Bounty of Ceres)

At some point, Ceres was home to the Cerulians, who used cerulium to create a two-class system, the Masters and the Scribes. The Masters incorporated cerulium into bracelets and used them to control the Scribes, which they would use as slaves. Eventually a symbiotic relationship developed between the two; the Master was enchanted by the Scribes, who had no thought but to compliment and assist the Master. They were so amused with one another that they were oblivious to the threat of an incoming asteroid which destroyed their civilisation. Chunks of cerulium remained, some of which came to Earth in 2050 and were used by Inspector Drake in his plan to create a mindless population of obedient drones. However, K9 destroyed all the bracelets and foiled the plan. (TV: Sirens of Ceres)

Ceres was later visited by the First Doctor, Vicki and Steven. By this time, the dwarf planet was devoid of any native life forms. A Cobalt Corporation mining base was located on Ceres. (AUDIO: The Bounty of Ceres)