The BBC wrote:American astronomers say they have strong evidence that there is a ninth planet in our Solar System orbiting far beyond even the dwarf world Pluto.
http://www.bbc.com/news/science-environment-35365323
Nemisis - Home of the Black Moon Clan
Seiren - Girls Bravo https://en.wikipedia.org/wiki/Girls_Bravo
Mondas - Origin planet of the Cybermen - Doctor Who - https://en.wikipedia.org/wiki/Mondas