Editing Life on Mars (section)

==Early speculation==
{{See also|Martian canals}}
{{multiple image
| align = right
| image1 = Karte Mars Schiaparelli MKL1888.png
| width1 = 220
| alt1 = 
| caption1 = Historical map of Mars from [[Giovanni Schiaparelli]]
| image2 = Lowell Mars channels.jpg
| width2 = 220
| alt2 = 
| caption2 = Mars canals illustrated by astronomer [[Percival Lowell]], 1898
| footer = 
}}

[[Martian polar ice caps|Mars's polar ice caps]] were discovered in the mid-17th century.{{citation needed|date=March 2021}} In the late 18th century, [[William Herschel]] proved they grow and shrink alternately, in the summer and winter of each hemisphere. By the mid-19th century, astronomers knew that [[Mars]] had certain other similarities to [[Earth]], for example that the [[Timekeeping on Mars|length of a day on Mars]] was almost the same as a day on Earth. They also knew that its [[axial tilt]] was similar to Earth's, which meant it experienced seasons just as Earth does—but of nearly double the length owing to its [[Darian calendar|much longer year]]. These observations led to increasing speculation that the darker [[albedo feature]]s were water and the brighter ones were land, whence followed speculation on whether Mars may be inhabited by some form of life.<ref name="Basalla">{{cite book|last1=Basalla|first1=George|title=Civilized life in the universe: scientists on intelligent extraterrestrials|date=2006|publisher=Oxford University Press|location=New York|isbn=9780195171815|page=[https://archive.org/details/civilizedlifeinu0000basa/page/52 52]|url=https://archive.org/details/civilizedlifeinu0000basa/page/52}}</ref>

In 1854, [[William Whewell]], a fellow of [[Trinity College, Cambridge|Trinity College]], Cambridge, theorized that Mars had seas, land and possibly life forms.<ref>{{cite web|url=https://mars.nasa.gov/allaboutmars/mystique/history/1800/|title=1800s {{!}} Mars Exploration Program|last=mars.nasa.gov|website=mars.nasa.gov|access-date=March 23, 2018|archive-url=https://web.archive.org/web/20190110150909/https://mars.nasa.gov/allaboutmars/mystique/history/1800/|archive-date=January 10, 2019|url-status=live}}</ref> Speculation about life on Mars exploded in the late 19th century, following telescopic observation by some observers of apparent [[Martian canals]]—which were later found to be optical illusions. Despite this, in 1895, American astronomer [[Percival Lowell]] published his book ''Mars,'' followed by ''Mars and its Canals'' in 1906,<ref name="NYT-20151001">{{cite news|last=Dunlap |first=David W. |title=Life on Mars? You Read It Here First. |url=https://www.nytimes.com/2015/09/30/insider/life-on-mars-you-read-it-here-first.html |date=October 1, 2015 |work=[[New York Times]] |access-date=October 1, 2015 |url-status=live |archive-url=https://web.archive.org/web/20151001163353/http://www.nytimes.com/2015/09/30/insider/life-on-mars-you-read-it-here-first.html |archive-date=October 1, 2015 }}</ref> proposing that the canals were the work of a long-gone civilization.<ref>{{cite book |title=Is Mars habitable?: A critical examination of Professor Percival Lowell's book 'Mars and its canals,' with an alternative explanation |first=Alfred Russel |last=Wallace |location=London |publisher=Macmillan |date=1907 |oclc=263175453}}{{page needed|date=June 2013}}</ref> This idea led British writer [[H. G. Wells]] to write ''[[The War of the Worlds (novel)|The War of the Worlds]]'' in 1897, telling of an invasion by aliens from Mars who were fleeing the planet's [[desiccation]].<ref>Philip Ball, {{cite web | url = https://www.newstatesman.com/2018/07/war-of-the-worlds-2018-bbc-hg-wells | title = What the War of the Worlds means now| date = July 18, 2018}} ''New Statesman (America Edition)'' July 18, 2018</ref>

The 1907 book ''[[Is Mars Habitable?]]'' by British naturalist [[Alfred Russel Wallace]] was a reply to, and refutation of, Lowell's ''Mars and Its Canals''. Wallace's book concluded that Mars "is not only uninhabited by intelligent beings such as Mr. Lowell postulates, but is absolutely uninhabitable."<ref>Wallace, Alfred R. (1907). [https://books.google.com/books?id=Gs1HAAAAIAAJ ''Is Mars Habitable? A Critical Examination of Professor Percival Lowell’s Book 'Mars and its Canals,' with an Alternative Explanation''],  p. 110, Macmillan.</ref> Historian [[Charles H. Smith (historian)|Charles H. Smith]] refers to Wallace's book as one of the first works in the field of [[astrobiology]].<ref name="smi18">Smith, Charles H. (2018). [https://people.wku.edu/charles.smith/wallace/S730.htm ''Is Mars Habitable?'' (S730: 1907)]. The Alfred Russel Wallace Page. Western Kentucky University. Retrieved August 26, 2023.</ref>

[[Spectroscopy|Spectroscopic]] analysis of Mars's atmosphere began in earnest in 1894, when U.S. astronomer [[William Wallace Campbell]] showed that neither water nor oxygen were present in the [[Martian atmosphere]].<ref name="chambers">{{cite book |first=Paul |last=Chambers |title=Life on Mars; The Complete Story |place=London |publisher=Bland ford |date=1999 |isbn=978-0-7137-2747-0 |url-access=registration |url=https://archive.org/details/lifeonmarscomple00cham }}{{page needed|date=June 2013}}</ref> The influential observer [[Eugène Antoniadi]] used the 83-cm (32.6&nbsp;inch) aperture telescope at [[Meudon Observatory]] at the 1909 [[astronomical opposition|opposition]] of Mars and saw no canals, the outstanding photos of Mars taken at the new Baillaud dome at the [[Pic du Midi de Bigorre|Pic du Midi]] observatory also brought formal discredit to the Martian canals theory in 1909,<ref>[[Audouin Dollfus|Dollfus, A.]] (2010) "The first Pic du Midi photographs of Mars, 1909" [http://adsbit.harvard.edu//full/2010JBAA..120..240D/0000241.000.html]</ref> and the notion of canals began to fall out of favor.<ref name="chambers"/>