One day in 1877, it was reported that Italian astronomer Giovanni Schiaparelli had observed, through his telescope, canals on the surface of Mars. This apparent evidence of the existence of a Martian civilisation inspired H. G. Wells to write The War of the Worlds, which, in turn, inspired Orson Welles's famous radio news bulletin hoax (which led thousands of listeners across America to believe that they were actually listening to the live report of a martian invasion).
The ultimate cause of all the excitement? Schiaparelli's report of Martian channels ("canali"), possibly carved by ancient rivers or glaciers, was mistranslated into English as "canals." Despite Schiaparelli's protestations, many astronomers latched onto the notion of life on Mars, and public interest naturally exploded.
[In 1976, two Viking space probes landed on Mars to search for signs of life. The findings were inconclusive (as was the examination of a Martian meteorite in the late 1990s).]