In addition to creating the character of Tarzan the Ape Man, author Edgar Rice Burroughs also wrote a famous series of sci-fi novels starting with The Princess of Mars, written in 1912. More than a century later, Doctor Who plays with that idea, and even a vintage time period, with tonight’s episode, called “The Empress of Mars.” And not only does the titular heroine get a promotion, but the time period gets a reboot – because the Doctor and his companions not only revisit Mars, but show up there in 1881.