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For a time in the late 19th and early 20th centuries, it was erroneously believed that there were canals on Mars. These were a network of long straight lines in the equatorial regions from 60° N. to 60° S. Lat. on the planet Mars. They were first described by the Italian astronomer Giovanni Schiaparelli during the opposition of 1877, and confirmed by later observers. Schiaparelli called these ''canali'', which was translated into English as "canals". The Irish astronomer Charles E. Burton made some of the earliest drawings of straight-line features on Mars, although his drawings did not match Schiaparelli's. By the early 20th century, improved astronomical observations revealed the "canals" to be an optical illusion, and modern high resolution mapping of the Martian surface by spacecraft shows no such features. ==Controversy== Some people went so far as to propose the idea that the canals were irrigation canals built by a supposed intelligent civilization on Mars. Percival Lowell was a strong proponent of this view, pushing the idea much further than Schiaparelli, who for his part considered much of the detail on Lowell's drawings to be imaginary. Some observers drew maps in which dozens if not hundreds of canals were shown with an elaborate nomenclature for all of them. Some observers saw a phenomenon they called "gemination", or doubling - two parallel canals. Other observers disputed the notion of canals. The observer E. E. Barnard did not see them. In 1903, Joseph Edward Evans and Edward Maunder conducted visual experiments using schoolboy volunteers that demonstrated how the canals could arise as an optical illusion.〔Evans, J. E. and Maunder, E. W. (1903) "Experiments as to the Actuality of the 'Canals' observed on Mars", (MNRAS, 63 (1903) 488 )〕 This is because when a poor-quality telescope views many point-like features (e.g. sunspots or craters) they appear to join up to form lines. In 1907 the British naturalist Alfred Russel Wallace published the book ''Is Mars Habitable?'' that severely criticized Lowell's claims. Wallace's analysis showed that the surface of Mars was almost certainly much colder than Lowell had estimated, and that the atmospheric pressure was too low for liquid water to exist on the surface; and he pointed out that several recent efforts to find evidence of water vapor in the Martian atmosphere with spectroscopic analysis had failed. He concluded that complex life was impossible, let alone the planet-girding irrigation system claimed by Lowell. The influential observer Eugène Antoniadi used the 83-cm (32.6 inch) aperture telescope at Meudon Observatory at the 1909 opposition of Mars and saw no canals, the outstanding photos of Mars taken at the new Baillaud dome at the Pic du Midi observatory also brought formal discredit to the Martian Canals theory in 1909,〔(story of the Pic du Midi observatory )〕 and the notion of canals began to fall out of favor. Around this time spectroscopic analysis also began to show that no water was present in the Martian atmosphere.〔 The arrival of the United States' Mariner 4 by NASA in 1965, which took pictures revealing impact craters and a generally barren landscape, was the final nail in the coffin of the idea that Mars could be inhabited by higher forms of life. A surface atmospheric pressure of 4.1 to 7.0 millibars (410 to 700 pascals) and daytime temperatures of −100 degrees Celsius were estimated. No magnetic field〔 〕〔 〕 or Martian radiation belts〔 〕 were detected. William Kenneth Hartmann, a Mars imaging scientist from the 1960s to the 2000s, explains the "canals" as streaks of dust caused by wind on the leeward side of mountains and craters.〔(Robots On Mars Search And Catalog Red Planet ). Audio recording, supporting statement is approx. 34:00 after start.〕 In 2015, planetary scientists (of NASA/JPL/University of Arizona) detected hydrated salts at Hale crater, corroborating their original hypothesis that "canals" as streaks are indeed formed by liquid water. Sasselov and fredericks from Harvard University explain that "The canali that the Italian astronomer Schiaperelli observed in the 19th century are most likely the dry riverbeds and canyons that Martian water created millennia ago." Lujendra Ojha of the Georgia Institute of Technology (Georgia Tech) in Atlanta, lead author of a report published Sept. 28 by Nature Geoscience said: "We found the hydrated salts only when the seasonal features were widest, which suggests that either the dark streaks themselves or a process that forms them is the source of the hydration. In either case, the detection of hydrated salts on these slopes means that water plays a vital role in the formation of these streaks." 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Martian canal」の詳細全文を読む スポンサード リンク
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