In 1878 the Italian astronomer Giovanni Virginio turned his telescope on a little red dot in the night sky and noted some features which he later described as canali. The word means "channels" in Italian, but it was mistranslated as "canals".
The idea that there might be constructed waterways on Mars entered the public imagination and fuelled the belief that there might be intelligent life there, partly inspiring HG Wells to write The War of the Worlds.
However, with more powerful telescopes and, eventually, visits by space probes, the evidence for canals dwindled. It was suggested that Virginio's observations were the result of an eye condition. Now Professor Alfred McEwen, of the University of Arizona, has written a paper in Science on some new research. Using a satellite camera, scientists have identified craters in which dark, finger-like features appear and seem to flow down slopes during late spring. "We haven't found any good way to explain what we're seeing, without water," says McEwen. So channels, at least, if not canals, do exist on Mars, after all.