Martian canals

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 telescopes without photography.

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 that, with the possible exception of the natural canyon Valles Marineris, the "canals" were likely an optical illusion, and modern high-resolution mapping of the Martian surface by spacecraft supports this interpretation.

The similarities with Earth led them to interpret darker albedo features (for instance Syrtis Major) on the lighter surface as oceans.

[2] 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".

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.

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,[4] going much further than Schiaparelli, who for his part considered much of the detail on Lowell's drawings to be imaginary.

[7] 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.

"[10] Later in the same year, the arrival of the United States' Mariner 4 spacecraft debunked for good the idea that Mars could be inhabited by higher forms of life, or that any canal features existed.

[15] In hindsight, William Kenneth Hartmann, a Mars imaging scientist from the 1960s to the 2000s, hypothesized that the "canals" were streaks of dust caused by wind on the leeward side of mountains and craters.

[21] Following the popularization of the idea that they were artificial constructs by Lowell's books, they appeared in numerous works of fiction until the Mariner 4 flyby conclusively demonstrated that they did not exist.