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
Pioneer Terra Pioneer Terra Pioneer Terra is a region on the dwarf planet Pluto, north of Tombaugh Regio and east of Voyager Terra. It was discovered by the "New Horizons" spacecraft on 14 July 2015. It is named for the "Pioneer" program, which included "Pioneer 10" and "Pioneer 11", the first spacecraft to cross the asteroid belt and explore Jupiter and Saturn, as well as the first to explore the outer solar system; "Pioneer 6, 7, 8, and 9", which formed an "interplanetary weather network"; "Pioneer 1" through "5", which explored the Moon in various ways; and the Pioneer Venus project, consisting