In 1877 Giovanni Virginio Schiaparelli, an astronomer at the Milan Observatory in Italy, announced a finding that would have an unexpected though significant impact on astronomy. He announced the observation of "canali" on the surface of Mars.
Though the most accurate translation of "canali" would have been channels, it instead got translated to canals. With the recent completion of the Suez Canal the interpretation was taken that to mean large scale artificial structures had been discovered. In other words, evidence of intelligent life.
Debate raged over the findings with Schiaparelli himself remaining skeptical of claims that these canals were artificial.
The excitement over the canals on Mars took hold of a young man named Percival Lowell who embarked on a distinguished career in astronomy. He was one of the first to realize that the best places for observatories were not in the center of well lit, populated cities, but rather in the barren, isolated deserts and plains or on mountain tops. He was the driving force behind the creation of the Lowell Observatory in Flagstaff, Arizona. Before his death in 1916 he began a search for a ninth planet, beyond Neptune, which he believed to exist based on variations of Neptune's orbit. He was proven right in 1930 with the discovery of Pluto.
In the end, the mistranslation turned out the be a blessing. It prompted studies of all the planets in far more detail than had been done before and helped to fire the curiosity and launch the career of one of astronomy's most distinguished citizens.