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Why are the Martian canals no longer considered evidence of intelligent life?

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Planet TOI 700e — extraterrestrial life An illustration of the Earth-size planet TOI 700e orbiting within the habitable zone of its star. The habitable zone is the area around a star where liquid water, and thus possibly life, can survive on a planet's surface. Its Earth-size sibling, TOI 700d, can be seen in the distance.

The Martian canals are no longer considered evidence of intelligent life because they were proven to be optical illusions rather than physical structures.12

In the late 19th and early 20th centuries, astronomers like Giovanni Virginio Schiaparelli and Percival Lowell reported seeing long, straight linear markings on the surface of Mars. Lowell famously hypothesized that these were artificial canals constructed by intelligent beings to transport water from the polar caps.1

However, these observations were made at the very limit of telescopic resolution. It is now understood that the human eye, when straining to see faint details, can perceive disconnected natural features—such as craters and surface markings—as continuous, straight-line networks. The controversy was definitively settled by spacecraft missions, beginning with Mariner 4 in 1965. High-resolution images revealed a surface covered in craters and geological features, but no evidence of the artificial canal networks that had once captivated the public imagination.12