Zygor
The home planet of the Zygons was, by some accounts, called Zygor, (PROSE: The Bodysnatchers, HOMEVID: When Being You Just Isn't Enough) although others indicate it was nameless. (WC: Zygon Stats) It was known to be warmer than Earth and covered in water, which was in the form of lakes with a different mineral composition than those of Earth. There were also no icecaps on the planet. Native lifeforms of Zygor included the unaltered Skarasen and the Zygons. (TV: Terror of the Zygons)
At some point, Zygor was destroyed in a stellar explosion. (PROSE: Doctor Who and the Loch Ness Monster) In the 20th century, Broton said his world was destroyed in a "recent catastrophe", (TV: Terror of the Zygons) although his conception of time was unconnected to the human time-scale. (PROSE: Doctor Who and the Loch Ness Monster) According to one account, the planet was destroyed because of the Zygon war against the Xaranti. (PROSE: The Bodysnatchers) Most accounts agreed that the Zygons lost their world when it burned during the Last Great Time War, (TV: The Day of the Doctor, WC: Zygon Stats, PROSE: The Whoniverse) with Elizabeth I, who was posing as a Zygon in 1562, claiming it burned during the first days of the conflict. (TV: The Day of the Doctor)
Many Zygons were able to escape Zygor's destruction. They were forced to become nomadic refugees searching for a new planet. (PROSE: The Bodysnatchers) At least four groups of Zygons attempted to make Earth more like Zygor: those who arrived in the 12th century, (TV: Terror of the Zygons) those that arrived in the 16th century and plotted to invade in the 21st century, (TV: The Day of the Doctor) those that arrived in 1909, (PROSE: Sting of the Zygons) and those that arrived in the late-20th century. (HOMEVID: Zygon: When Being You Just Isn't Enough)
