H The "Canals" of Mars: How Percival Lowell Saw the Impact Basins

The "Canals" of Mars: How Percival Lowell Saw the Impact Basins

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

In 1888, Italian astronomer Giovanni Schiaparelli announced the discovery of a network of narrow lines on Mars, which he described as "canali," an Italian word that means "channels." In Italian, the word can mean a natural channel like a river valley. Schiaparelli's drawings show winding lines that look natural. Unfortunately, English speakers interpreted "canali" as "canals," which are artificial.

American Astronomer Percival Lowell became the principal champion of artificial canals and intelligent life on Mars. He claimed to have observed an elaborate network of narrow, straight lines on Mars that he believed were canals built to carry water from the polar ice caps to the equatorial regions. In many places he claimed numerous canals intersected in dark spots which he called "oases."

Even in Lowell's day, many astronomers rejected the canals. They claimed, correctly, that Mars was too cold for liquid water. Nobody ever managed to photograph a canal. We now have detailed maps of Mars, and the "canali" and canals do not exist. In fact, the "canals" run up and down slopes in many places, something real canals never do.

But Schiaparelli and Lowell were careful observers, and many of the larger objects they saw on Mars are real. So what were they seeing on Mars that they interpreted as "canali?" The question is not easy to answer because the positions of objects seen on Mars with the telescopes of 100 years ago are very inaccurate compared with locations mapped by spacecraft. They both saw the huge impact basins of Argyre, Hellas, and Isidis. On Lowell's map here, the northern rim of the Argyre Basin is the curving arc just below the large dark area at lower left. Hellas is the large oval at lower right with two crossing lines inside it, and Isidis is at upper right. They both saw the large dark regions in the southern hemisphere of Mars, although Lowell mapped only the darkest areas compared to Schiaparelli. They both agree, interestingly, in seeing a large dark spot surrounded by a light ring in the Tharsis Plateau. Some of Lowell's "oases" may be the huge shield volcanoes of Tharsis. Some of Schiaparelli's and Lowell's lines seem to correspond to the boundary between the northern lowlands and the southern highlands, and it is possible they may have been seeing shadows on sloping regions. Lowell had a tendency to connect faint details with lines, as we can see in his drawings of other planets, so many of the canals probably never were anything but chance alignments of faint details.

The story of Schiaparelli and Lowell is important. Any theory in science has to be able to be verified by other observers. It is very easy to connect random details into patterns that do not exist. Only if other people, using other methods, confirm the existence of a pattern can we say it is real.

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Created 21 August 2009, Last Update 15 January 2020