How did the idea that aliens inhabit Mars get started?
Just to add a little to what has already been said. The mindset of the time seems to have already been primed for the possibility of life on other planets, perhaps because the recently popularized (by Darwin and others) theory of evolution made it seem inevitable. Mars was most readily observable, particularly given the astronomcal equipment of the time, and in many ways seemed most earthlike. The nature of its atmosphere was still “up in the air”. (Sorry, that didn’t register with me as a pun originally, but then I couldn’t stop myself.) Schiaparelli described “canali” which might have better been translated as “channels”, but which of course was translated “canals”, in a lazy or unskillful handling of the Italian. He didn’t initially propose that they were artificial, but in the English-speaking world, canals are man-made objects, and some spectacular earth-bound projects had recently been completed (Suez, 1869) or attempted (Panama, 1880). Lowell’s imagination was fired, and Schiapa
