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.
"To determine whether a planet be the abode of life, two questions about it must be answered in turn: first, are its physical conditions such as to render it habitable? And secondly, are there any signs of its actual habitation? Unless we can answer the first point satisfactorily, it were futile to seek for evidence of the second."