This article originally appeared in The Skeptic, Volume 5, Issue 1, from 1991.
Today it is widely know that people once believed that there were canals on Mars. But the story behind this strange state of affairs is much less well known. The astronomical data in the following account comes from William Sheehan’s Planets and Perception, an excellent account of the story.
During the nineteenth century, telescopes increased in size and quality and Mars naturally became the subject of increased observation. The best views of it are obtained approximately every two years, when Earth lies between Mars and the sun (this is known as an ‘opposition’). The distance between the two planets at opposition ranges from 34.6 million miles (55.7 million km) to 62.9 million miles (101.3 million km). This results in significant differences in the quality of Earth-based observations with the best oppositions occurring every 15 years.
In the opposition of 1877, Mars was only 35 million miles away; Asaph Hall in the USA discovered its two moons, and Giovanni Schiaparelli in Italy drew the best map of Mars of that time, also inventing the modem naming system for Martian features. He copied some of the existing naming systems in calling dark coloured areas after bodies of water and lighter areas after lands and deserts. Connecting the dark areas he drew a large number of canali – which in Italian means channel or canal. Although past astronomers had also observed canali, Schiaparelli was the first to mark them in such numbers and to draw attention to them.
Schiaparelli confirmed the existence of the canali during the oppositions of 1879 and 1881, but in these drawings they became significantly straighter and narrower. He also saw that many of these canali had ‘germinated’, such that they were actually two narrowly separated lines. The name, their straightness and germination all suggested they were artificial, but on this fact Schiaparelli always remained unsure.
Other astronomers agreed there was something where Schiaparelli drew his canals, as they were by then being called in English, but they believed he had simplified what was really there. Although they remained unconfirmed, his observations were not dismissed because of his high reputation, gained in the 1860s for his work on meteors. This led to many observers assuming that their inability to see the canals was a reflection on their own lesser observational skills.
In 1886 independent confirmation of Schiaparelli ‘s canal observations was made, and reported in the prestigious journal Nature (3 June 1886). By 1890 the existence of canals was generally accepted by astronomers. Almost all the maps of Mars produced at that time showed them, many even in the same positions as those of Schiaparelli.
To understand why other observers confirmed the canals some knowledge of how Mars was observed is required. Because of atmospheric interference, the view of the Martian surface is normally neither clear nor persistent but is constantly fluctuating, with details only sharp for brief moments. Hence observers had to be selective in which details they recorded. So observers who knew the layout of the canals would know which details to record as canals. Observers had to go by eye in planetary observation at this time because photography was too slow, only being good enough to record the coarsest features.
Great things were expected from the 1892 opposition, in which Mars would make its closest approach to Earth since 1877, but unfortunately the best views were obtained from the southern hemisphere, away from the best telescopes. Edward Pickering at Arequipa in Peru reported seeing lakes on the Martian surface. Other astronomers reported high altitude clouds, and some publicly claimed that these were attempts by the Martian inhabitants to communicate with Earth.
Following this, two events occurred which may have affected the later developments of the canal story by their influence on Percival Lowell. In 1892 the French astronomer Camille Flammarion published La Planete Mars. A believer since the 1860s in life on other worlds, he interpreted the canals as proof of Martian habitation. In his book he assumed the canals were indeed waterways, and described how Mars, being an older world, might contain a more advanced and wiser human race. The second event was a paper published in 1893 by Schiaparelli, in which he argued that Mars had a significant atmosphere, ice-covered polar regions and temperatures similar to those of Earth. Although he supported the highly geometric appearance of the water carrying canals he argued they had been created naturally.
Not until 1894 did Percival Lowell, the person now most associated with the canals, enter the story. Lowell came from a wealthy family in Boston, Massachusetts. A gifted mathematician, he declined an offer to teach at Harvard, travelling to Europe instead. On his return he chose to work in his grandfather’s textile business for six years. Between 1883 and 1892 he made three journeys to the Far East and his interest in this area led to four books. An amateur astronomer, Lowell was so taken by Schiaparelli’s canal observations that he decided to devote his own time and money to their study. He wanted to build an observatory somewhere in the American west where he believed the air was better. Returning to Boston in December 1893 he was given a copy of La Planete Mars. In January he, Picketing and others went west, reaching Tombstone, Arizona in March. They tested various sites, finally choosing one near Flagstaff. On May 31 they made their first observations of the 1894 opposition.
Schiaparelli’s 1893 paper and Flammarion’s book provided the outline of Lowell’s own theory, which he formed after only two months observation of Mars. It generated great public interest, inspired HG Wells’ War of the Worlds and he continued to promote and defend his ideas until his death in 1916. His theory was as follows.
He noticed there were canals in the dark areas, areas which other observers had assumed to be seas. With this and other evidence he realised that Mars must be almost all desert. Mars was smaller than Earth and had therefore aged more quickly, and so any intelligent races would also be at a later stage of evolution. The ancient, peaceful Martian civilisation – desperate for water – had constructed a planet-wide canal system. With the end of winter the polar ice melted and the water was carried by the canals to the drier equatorial regions. In Lowell’s view, the dark lines on Mars were not the canals, however; they were actually strips of irrigated vegetation growing on either side of the canals. These strips ranged in width from 2 miles to about 30 miles and could be over 2000 miles long. The interest of the general public was increased by Lowell’s claim that this planetary desertification would also happen on Earth, the existence of deserts demonstrated that it had already started.
Lowell promoted his theory in a series of lectures and magazine articles, and in December 1895 he published Mars, discussed what had been observed, designed a possible planetary canal system and speculated on what Martian society might be like.
In July 1896 Lowell and his assistants began new observations which generated greater criticism than their Martian results. They recorded lines on both Venus and Mercury, and one observer saw lines on a satellite of Jupiter. Most of the lines on Venus radiated from a central point like spokes of a wheel. For Lowell to claim he saw the surface repeatedly when most astronomers agreed that Venus was covered by a layer of clouds sowed doubt in the minds of some of those who supported him over the canals.
During the 1890s some objections to the canal theories were raised. In 1894 Edward Maunder explained how the canals could just be a series of separate dark areas, ‘lakes’ not ‘canals’. In 1903 he and JE Evans performed what Lowell later called the ‘small boy theory’. They found that when a disc containing dot-like markings was viewed from a great enough distance, their volunteers (boys from a Greenwich school) drew canals. Lowell correctly responded that this only showed what might be the cause, not what actually was.
Photographic evidence of the canals was finally obtained at Lowell Observatory during the 1905 opposition. Of the experts who viewed the quarter inch diameter images, half saw canals and half did not. Subsequent photographs obtained in 1907 and 1909 were no more decisive. Eugene Antoniadi had seen many canals while working with Flammarion in the years 1895 to 1902. In 1903 the small boy theory, together with his existing doubts about the canals, led him to publish one of the first maps of Mars for 25 years which showed no canals. During the 1909 opposition he observed Mars using the largest telescope in Europe. The atmosphere was so good that on his first night’s viewing he saw the surface of Mars for seven hours. He saw no canals or lines just ‘a prodigious and bewildering amount of sharp or diffused natural, irregular detail.’ (Sheehan 1988, p. 244 ). Similar conclusions were reached by many other astronomers.
In the following years supporters of the canals made more use of photography as the technology improved. As late as 1962 Earl Slipher (who had worked with Lowell) published a photographic atlas showing the canals, but once again while some could see the canals others could not (Mutch 1976). It was not until 1965 when the spacecraft Mariner 4 passed Mars and returned photos showing no signs of canals that the controversy finally ended.
So, the big question remains: why did people see the canals? The answer comes from the study of perception. Schiaparelli, in 1877, observed surface features at the limit of resolution for the type of telescope he used. Atmospheric interference permitted only brief glimpses of surface features and colours. His mind had to build an image from these and the canals were part of the structure it built. Later observers had the same problem but the maps of Schiaparelli gave them an idea as to how their glimpses of the surface of Mars should be interpreted.
The idea of canals on Mars may be charming, but alas, it is without foundation.
Notes
- Percival Lowell’s three books on Mars are Mars (1895), Mars and its Canals (1906) and Mars as the Abode of Life (1908).
- For a detailed account see William Sheehan’s Planet and Perception: Telescopic views and interpretations, 1609-1909 (1988). For good short accounts see The Planets, by Peter Francis (1981), and The Geology of Mars by T A Mutch et al ( 1976).
