Martian canal

During the late 19th and early 20th centuries, it was erroneously believed that there were "canals" on the planet Mars. These were a network of long straight lines in the equatorial regions from 60° north to 60° south latitude on Mars, observed by astronomers using early low-resolution telescopes without photography. 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. Around the turn of the century there was even speculation that they were engineering works, irrigation canals constructed by a civilization of intelligent aliens indigenous to Mars. 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.

History
The Italian word canale (plural canali) can mean "canal", "channel", "duct" or "gully". 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 &mdash;for example, he used the name "Canale Atlantico" for what later came to be called Syrtis Major Planum.

Considering their primitive astronomical instruments, it is not really surprising that respectable scientists saw features on Mars which were not there. 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. Astronomers believed at the time 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. The similarities with Earth led them to interpret darker albedo features (for instance Syrtis Major) on the lighter surface as oceans. By the late 1920s, however, it was known that Mars is very dry and has a very low atmospheric pressure.

In 1889, American astronomer Charles A. Young reported that Schiaparelli's canal discovery of 1877 had been confirmed in 1881, though new canals had appeared where there had not been any before, prompting "very important and perplexing" questions as to their origin.

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. 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.

Interpretation as engineering works
The hypothesis that there was life on Mars originated from seasonal changes observed in surface features, which began to be interpreted as due to seasonal growth of plants (in fact, Martian dust storms are responsible for some of this).

During the 1894 opposition, 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 American astronomer Percival Lowell and a few others. The visible seasonal melting of Mars polar icecaps fueled speculation that an advanced alien race indigenous to Mars built canals to transport the water to drier equatorial regions. Newspaper and magazine articles about Martian canals and "Martians" captured the public imagination. Lowell published his views in three books: Mars (1895), Mars and Its Canals (1906), and Mars As the Abode of Life (1908). He remained a strong proponent for the rest of his life of the idea that the canals were built for irrigation by an intelligent civilization, going 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. The late 19th century was a time of construction of giant infrastructure projects of all kinds, and particularly canal building. For instance, the Suez Canal was completed in 1869, and the abortive French attempt to build the Panama Canal began in 1880. It is understandable that 19th century people who accepted the idea of a Mars inhabited by a civilization might interpret the canal features as giant engineering works.

Doubts
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. 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. Based on his own experiments, Lowell's assistant, A. E. Douglass, was led to explain the observations in essentially psychological terms. 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, 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. However, as of 1916 Waldemar Kaempffert (editor of Scientific American and later Popular Science Monthly) was still vigorously defending the Martian canals theory against skeptics.

Spacecraft evidence
The arrival of the United States' Mariner 4 spacecraft 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, or that any canal features existed. A surface atmospheric pressure of 4.1 to 7.0 millibars (410 to 700 pascals), 0.4% to 0.7% of Earth atmospheric pressure, 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.

In popular culture
"A clement twilight zone on a synchronously rotating Mercury, a swamp‐and‐jungle Venus, and a canal‐infested Mars, while all classic science‐fiction devices, are all, in fact, based upon earlier misapprehensions by planetary scientists."

- Carl Sagan, 1978

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.
 * Camille Flammarion's Uranie (1889, published as Urania in English in 1890) include descriptions of life on Mars; "They have straightened and enlarged the watercourses and made them like canals, and have constructed a network of immense canals all over the continents. The continents themselves are not bristling all over with Alpine or Himalayan upheavals like those of the terrestrial globe, but are immense plains, crossed in all directions by canals, which connect all the seas with one another, and by streams made to resemble canals."
 * Garrett P. Serviss' Edison's Conquest of Mars (1898) repeatedly mentions Schiaparellian canals (which play a key part in the denouement of the story), but does not describe them in detail, apparently considering them simply irrigation canals comparable to those on Earth — ignoring the fact that, in that case, they could hardly be visible from Earth. Serviss' Mars also has lakes and oceans.
 * George Griffith's A Honeymoon in Space (1900) describes the canals as the remnants of gulfs and straits "widened and deepened and lengthened by... Martian labour".
 * Carl Jung's inaugural dissertation for his medical degree, On the Psychology and Pathology of So-Called Occult Phenomena (1902), describes the recounts of a 15-year-old patient, a medium who encountered supernatural beings during seance: "she told us all the peculiarities of the star-dwellers:... the whole of Mars is covered with canals, the canals are all flat ditches, the water in them is very shallow. The excavating of the canals caused the Martians no particular trouble, as the soil there is lighter than on earth."
 * Edgar Rice Burroughs' influential A Princess of Mars (1912) describes an almost entirely desert Mars, with only one small body of liquid water on the surface (though swamps and forests appear in the sequels). The canals, or waterways as Burroughs calls them, are still irrigation works, but these are surrounded by wide cultivated tracts of farmland which make their visibility somewhat credible.
 * Alexander Bogdanov's Engineer Menni (1913) details the social, scientific, and political history of the construction of the Martian canals and the socio-economic ramifications the construction had on Martian society.
 * Otis Adelbert Kline's Outlaws of Mars (1933) has multiple parallel canals, surrounded by walls and terraces, and describes the construction of the canals by Martian machines.
 * In Stanley G. Weinbaum's A Martian Odyssey (1934) the lead character Jarvis crosses several canals: One is "a dry ditch about four hundred feet wide, and straight as a railroad on its own company map." Some canals have "mud cities" and vegetation beside them.  One appears to be covered with what looks like a nice green lawn, but turns out to be hundreds of small creatures that move out of the way when approached.  In the sequel Valley of Dreams (1934) it is discovered that the various races on Mars cooperatively maintain the canal system, driving water northward from the southern polar icecap.
 * "Seeds of the Dusk" (1938) is a short story by Raymond Z. Gallun about a far-future twilight race of humans and animals on earth that are threatened by a newcomer plant that can defend itself adaptively, even killing an attacker. As it propagates and links in long chains with others of its species, the linked chains of plants begin pumping water through their specially formed inner chambers. At the end it is made apparent that the spores of the plant had drifted to Earth from Mars, and it was beginning to form long canals on Earth as it had done on Mars.
 * In Out of the Silent Planet (1938), C. S. Lewis depicts the "canals" (handramit in Martian) as vast rifts in the surface of an almost airless Mars, in which the only breathable atmosphere and water have collected where life is possible, the rest of Mars being entirely dead. The handramit were made during a vast engineering project undertaken long ago by the Martians to save what was left of their planet after Mars was attacked and devastated by the evil Guardian Angel of Earth.
 * In the Captain Future book Outlaw World (1946), it is stated that Mars is kept alive by the ancient canal system carrying water from its polar caps. The most tightly kept secret of the planet is that radium powered engines are required to keep the water flowing.
 * Robert A. Heinlein gave two depictions of the Martian canals:
 * In The Green Hills of Earth (1947), the blind poet Rhysling, composes "The Grand Canal", describing the beauty of Mars' main canal as he saw it when first arriving on Mars. Having later become blind,  Rhysling does not realize that human colonists have proceeded in short order to heavily pollute the canals with industrial wastes, tear down half of the delicate beautiful structures at the canal side and convert the other half to industrial uses – with the remnant of the indigenous Martians helpless to stop them.
 * In Red Planet (1949), colonists use the frozen canals for travel and a seasonal migration (by iceboat during winter when the canals are frozen and by boat when the ice melts during the Martian summer). Teenagers Jim Marlowe and Frank Sutton set out to skate the thousands of miles to their homes on the frozen Martian canals when escaping the Lowell Academy boarding school.
 * The 180,000 year old narrator of Fredric Brown's "Letter to a Phoenix" (1949) mentions he was one of the people digging the canals.
 * In Ray Bradbury's The Martian Chronicles (1950), the canals are artificial waterways stretching between stone banks, filled with blue water, or sometimes poetically described as full of "green liquors" or "lavender wine". Bradbury revisited the martian canals in 1967 in his short story "The Lost City of Mars".
 * In Lester del Rey's Marooned on Mars (1952), the canals turn out to be a broad vine-like plant growing a vast distance across the planet's surface.
 * In the BBC radio production Journey into Space: The Red Planet (1954–1955), the canals are valleys filled with a plant life resembling giant rhubarbs.
 * In Robinson Crusoe on Mars (1964) Kit Draper and Friday flee from the enemy aliens through the underground canals on their way to the polar ice cap.
 * In Colin Greenland's Take Back Plenty (1990), humans arriving on Mars discover a networks of canals in very bad condition due to the long period since the original builders became extinct. Human colonists energetically renovate the canals and put them to renewed use, discover at the Grand Canal the colossal buried city of the original builders, excavate it and build a thriving human city all around it. The human city is named "Schiaparelli".
 * The Mars of the steampunk role-playing game Space: 1889 (1988) is crisscrossed by artificial canals which support cities inhabited by the ancient civilization of the Canal Martians.
 * The 1991 computer game Ultima: Martian Dreams features a plot based around Victorian expeditions to Mars. The Martian canals play a very prominent role as the main characters have to find a way to refill them using ice from the polar caps.
 * Kim Stanley Robinson's science fiction chronicling of the terraforming of Mars in the Mars trilogy (1993–1999) and 2312 (2012) features the creation of canals on Mars ("burned" into the land with magnified sunlight) with the Lowell maps as inspiration. "Thus a nineteenth-century fantasy forms the basis for the actual landscape."
 * In S. M. Stirling's 2008 In the Courts of the Crimson Kings alternate history novel Mars is terraformed and seeded with earth life including early humans, at some point in prehistory. The humans of Mars do indeed build a planet wide canal network due to their world's exceptional dryness, however it's left ambiguous whether or not these were what Lowell actually saw in the 19th century.
 * Ken Kalfus's 2013 novel, Equilateral, is based entirely on the supposed existence of "man"-made Martian canals and on the construction of a vast triangle in the Arabian desert in order to communicate with the Martian beings.
 * Scott Walker's "Lullaby" from the 2014 album Soused (with Sunn O)))) contains the lyrics, "Tonight my assistant will hear the canals of Mars." The composition first appeared on Ute Lemper's 2000 album, Punishing Kiss.

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.