Mars
As telescopes brought Earth’s planetary neighbors into closer view, Lowell, an astronomer, proffered a bold theory about the nature of faint lines glimpsed on the surface of the Red Planet. They were, he deduced, irrigation canals built by intelligent Martian life forms. Though his colleagues were skeptical, Lowell’s conjecture helped popularize the field of astronomy, and his later work—his search for “Planet X”—paved the way for the discovery of Pluto.