In 1877, Italian astronomer Giovanni Schiaparelli spotted linear features on Mars, which he called canali. However, a mistranslation of this word contributed to a widespread misconception that the planet was home to an alien civilization.
American astronomer Percival Lowell became obsessed with these markings, interpreting them as evidence for a sophisticated network of water-transportation channels. His work built upon Schiaparelli’s observations and fueled a public fascination with the idea of Martian life.
The notion of extraterrestrial life was gaining traction in the late 19th century, coinciding with major breakthroughs in biology and astronomy. Charles Darwin’s theory of natural selection (1858) and the invention of the spectroscope (1864) revealed that other planets were likely composed of similar elemental materials as Earth.
If life evolved naturally on Earth and planets formed in a similar manner, it seemed logical to assume that life could also emerge on Mars. The idea of Martian canals sparked an alien craze in early 20th-century America, showcasing the public’s desire for answers about the mysteries of the universe.
Source: https://www.scientificamerican.com/article/in-the-search-for-life-beyond-earth-the-only-constant-is-hope