Gallifrey's moon
According to the work of one Gallifreyan author, the First Doctor took Gallifrey's moon with him when he escaped Gallifrey. (PROSE: A Brief History of Time Lords)
Across its history, the planet Gallifrey in fact had at least three moons. An unnamed satellite, the heavily industrialised Pazithi Gallifreya (COMIC: Agent Provocateur) and the lost moon, Botoya. Built into the latter was a device that could rewrite history on a grand scale, which was why the Doctor suspected the Ancients of Gallifrey had hidden the moon. Botoya subsequently became a legend in Gallifreyan culture, one not widely believed in. (AUDIO: The End of the Beginning)