Bradbury is of a generation of sci-fi writers who used allegory and metaphors to deftly explore humanity and the human mind, even while literally writing about aliens. Bradbury isn't trying to prove that aliens exist on Mars. Rather, the book, really a collection of short stories, allows people to wonder about the sustainability of their own civilization. This is probably one of the best of Bradbury's works. (By the way, this book was later made into a haunting computer game.)