Open the official 1962 U.S. government map of Mars and you will find a detailed network of canals carved across the planet. Three years later, Mariner 4 flew past and revealed a dead, cratered rock with less than 1 percent of Earth's atmospheric pressure. This episode traces how nearly a century of astronomical wishful thinking put an alien engineering project on an official map.

We follow the story from Angelo Secchi's use of the Italian word canali in 1858 and Giovanni Schiaparelli's 1877 map, through the mistranslation of channels as canals, to Percival Lowell's Flagstaff observatory and his books about a dying civilization irrigating a desert world. Along the way, Alfred Russel Wallace's 1907 thermodynamic critique, Eugene Antoniadi's 1909 observations through an 83-centimeter telescope, and a 1903 schoolboy experiment show how physics, ...