As skywatchers prepared for the return of Halley's comet in 1910, they heard some alarming scientific predictions: Poisonous gases in the comet's tail might "snuff out all life on the planet," "leaving the burnt and drenched Earth no other atmosphere than the nitrogen now present in the air." How should a responsible citizen evaluate a dire prediction by a minority of experts? In this week's episode of the Futility Closet podcast, we explore the Halley's hysteria, remember the alarming predictions made for Y2K, and recall a forgotten novella in which Arthur Conan Doyle imagined a dead Earth fumigated by cosmic ether.We also consider the odd legacy of an Australian prime minister who disappeared in 1967, investigate the role of balloon-borne sheepdogs during the Siege of Paris, learn why Mark Twain's brother telegraphed the entire Nevada constitution to Washington D.C. in 1864, and offer a chance to win a book in the next Futility Closet Challenge.