Alfred Russel Wallace
Astrobiology

Wallace's 1904 book Man's Place in the Universe was the first serious attempt by a biologist to evaluate the likelihood of life on other planets. He concluded that the Earth was the only planet in the Solar System that could possibly support life, mainly because it was the only one in which water could exist in the liquid phase. His treatment of Mars in this book was brief, and in 1907, Wallace returned to the subject with the book Is Mars Habitable? to criticise the claims made by the American astronomer Percival Lowell that there were Martian canals built by intelligent beings. Wallace did months of research, consulted various experts, and produced his own scientific analysis of the Martian climate and atmospheric conditions. He pointed out that spectroscopic analysis had shown no signs of water vapour in the Martian atmosphere, that Lowell's analysis of Mars's climate badly overestimated the surface temperature, and that low atmospheric pressure would make liquid water, let alone a planet-girding irrigation system, impossible. Richard Milner comments that Wallace "effectively debunked Lowell's illusionary network of Martian canals." Wallace became interested in the topic because his anthropocentric philosophy inclined him to believe that man would be unique in the universe.
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