Martian canal

1877 map of Mars by Giovanni Schiaparelli.

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

Mars as seen through 6 inch (15 cm) aperture reflecting telescope, as Schiaparelli may have seen it.

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,[1] 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.[2] 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.[3] 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.[4] 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,[5] 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.[3]

Mars surface by Mariner 4 in 1965

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[6][7] or Martian radiation belts[8] 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.[9]

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.[10] 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." [11]

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." [10]

History of canals

Martian channels depicted by Percival Lowell

The Italian word canale (plural canali) can mean "canals" (including artificial canals or ducts) or "channels" or "gullies".[12] The first person to use the word canale in connection with Mars was Angelo Secchi in 1858, although he did not see any straight lines and applied the term to large features —for example, he used the name "Canale Atlantico" for what later came to be called Syrtis Major Planum.

It is not necessarily odd that the idea of Martian canals was so readily accepted by many. At this time in the late 19th century, astronomical observations were made without photography. Astronomers had to stare for hours through their telescopes, waiting for a moment of still air when the image was clear, and then draw a picture of what they had seen. They saw some lighter or darker albedo features (for instance Syrtis Major) and believed that they were seeing oceans and continents. They also believed that Mars had a relatively substantial atmosphere. They knew that the rotation period of Mars (the length of its day) was almost the same as Earth's, and they knew that Mars' axial tilt was also almost the same as Earth's, which meant it had seasons in the astronomical and meteorological sense. They could also see Mars' polar ice caps shrinking and growing with these changing seasons. It was only when they interpreted changes in surface features as being due to the seasonal growth of plants that life was hypothesized by them (in fact, Martian dust storms are responsible for some of this). By the late 1920s, however, it was known that Mars was very dry and had a very low atmospheric pressure.

In addition, the late 19th century was a time of great canal building on Earth. For instance, the Suez Canal was completed in 1869, and the abortive French attempt to build the Panama Canal began in 1880. It is natural that some thought similar projects were being undertaken on Mars. In 1889, astronomer Charles A. Young reported that Schiaparelli's canal discovery of 1877 had been confirmed in 1881, though new canals had appeared where there hadn't been any before, prompting "very important and perplexing" questions as to their origin.[13]

During the favourable opposition of 1892, W. H. Pickering observed numerous small circular black spots occurring at every intersection or starting-point of the "canals". Many of these had been seen by Schiaparelli as larger dark patches, and were termed seas or lakes; but Pickering's observatory was at Arequipa, Peru, about 2400 meters above the sea, and with such atmospheric conditions as were, in his opinion, equal to a doubling of telescopic aperture. They were soon detected by other observers, especially by Lowell.

During the oppositions of 1892 and 1894, seasonal color changes were reported. As the polar snows melted the adjacent seas appeared to overflow and spread out as far as the tropics, and were often seen to assume a distinctly green colour. The idea that Schiaparelli's canali were really irrigation canals made by intelligent beings, was first hinted at, and then adopted as the only intelligible explanation, by Lowell and a few others. Newspaper and magazine articles about Martian canals captured the public imagination.

At this time (1894) it began to be doubted whether there were any seas at all on Mars. Under the best conditions, these supposed 'seas' were seen to lose all trace of uniformity, their appearance being that of a mountainous country, broken by ridges, rifts, and canyons, seen from a great elevation. These doubts soon became certainties, and it is now universally agreed that Mars possesses no permanent bodies of surface water.

In popular culture

Although the concept of the canals had been available since Schiaparelli's 1877 description of them, early fictional descriptions of Mars omitted these features. They receive no mention, for instance, in H. G. Wells' The War of the Worlds (1897), which describes a slowly drying Mars, covetous of Earth's resources, but one which still has dwindling oceans such as are depicted on Schiaparelli's maps. Later works of fiction, influenced by the works of Lowell, described an ever-more arid Mars, and the canals became a more prominent feature, though how they were explained varied widely from author to author.

List of canals

The canals were named, by Schiaparelli and others, after real and legendary rivers of various places on Earth or the mythological underworld.

See also

References

  1. ↑ Dunlap, David W. (October 1, 2015). "Life on Mars? You Read It Here First.". New York Times. Retrieved October 1, 2015.
  2. ↑ Evans, J. E. and Maunder, E. W. (1903) "Experiments as to the Actuality of the 'Canals' observed on Mars", MNRAS, 63 (1903) 488
  3. 1 2 Chambers P. (1999). Life on Mars; The Complete Story. London: Blandford. ISBN 0-7137-2747-0.
  4. ↑ Wallace, Alfred. "Is Mars Habitable (S730: 1907)". The Alfred Russel Wallace Page hosted by Western Kentucky University. Retrieved 2007-05-13.
  5. ↑ story of the Pic du Midi observatory
  6. ↑ O'Gallagher, J.J.; Simpson, J.A. (1965-09-10). "Search for Trapped Electrons and a Magnetic Moment at Mars by Mariner IV". Science, New Series 149 (3689): 1233–1239. Bibcode:1965Sci...149.1233O. doi:10.1126/science.149.3689.1233. PMID 17747452.
  7. ↑ Smith, Edward J.; Davis Jr.; Leverett; Coleman Jr.; Paul J.; Jones, Douglas E. (1965-09-10). "Magnetic Field Measurements Near Mars". Science, New Series 149 (3689): 1241–1242. Bibcode:1965Sci...149.1241S. doi:10.1126/science.149.3689.1241. PMID 17747454.
  8. ↑ Van Allen, J.A.; Frank, L.A.; Krimigis, S.M.; Hills, H.K. (1965-09-10). "Absence of Martian Radiation Belts and Implications Thereof". Science, New Series 149 (3689): 1228–1233. Bibcode:1965Sci...149.1228V. doi:10.1126/science.149.3689.1228. PMID 17747451.
  9. ↑ Robots On Mars Search And Catalog Red Planet. Audio recording, supporting statement is approx. 34:00 after start.
  10. 1 2 Anderson, Gina. "NASA Confirms Evidence That Liquid Water Flows on Today’s Mars". NASA. Retrieved 2015-11-09.
  11. ↑ "Super-Earths And Life". courses.edx.org. Retrieved 2015-11-09.
  12. ↑ WordReference.com
  13. ↑ Young, Charles A. "A Textbook of General Astronomy. 1889. Ginn and Co. Boston.
  14. ↑ Robinson, Kim Stanley (2012). 2312. New York: Orbit. pp. 554–555. ISBN 978-0-316-19280-4.

External links

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