The Tenth Planet of malevolent cyborgs that became a recurring adversary in later "Doctor Who" stories. The "tenth planet" in the title makes reference to a fictional lost planet in Earth's Solar System; at the time of production, the Solar System was generally held to consist of nine planets, prior to the redesignation of Pluto as a minor planet. "The Tenth Planet" is an incomplete "Doctor Who" serial – one of many serials that were affected by the BBC's policy of wiping archived programmes in the 1960s and 70s. Only three of the four episodes are currently held in the BBC archives; the
Gustav Holst Guide": "The Planets" (recordings under Boult on HMV and Nixa, and another under Sir Malcolm Sargent on Decca); the "Perfect Fool" ballet music; the "St Paul's Suite"; and three short choral pieces. In the stereo LP and CD eras numerous recordings of "The Planets" were issued, performed by orchestras and conductors from round the world. By the early years of the 21st century most of the major and many of the minor orchestral and choral works had been issued on disc. The 2008 issue of "The Penguin Guide to Recorded Classical Music" contained seven pages of listings of Holst's works