Well, there is a reason. In fact there are two. One was called Giovanni Schiaparelli and the other Percival Lowell. Without them we wouldn’t have Martians and Americans would never have fallen for Orson Welles’ 1938 hoax broadcast about an interplanetary invasion. Schiaparelli, director of the Milan observatory, fell in love with Mars when he first saw it in 1877. The planet was unusually close to Earth and he was able to observe it in detail - or so he thought. Straight lines criss-crossed the surface. The distinguished Italian astronomer had no trouble naming them. They were clearly “canali”. “Canali” means channels. Unfortunately it sounds as if it means canals, and that was how the English-speaking press translated it.

The crucial difference between a channel and a canal is that one is natural and the other isn’t. Schiaparelli’s discovery proved there was life on Mars. And not just any old life. A master race had constructed these huge canals to bring melt water down from the ice caps to irrigate the parched central plains.

At least that is what Percival Lowell said. The American astronomer, who wasn’t short of a dollar or two, founded the Lowell observatory at Flagstaff, Arizona, in 1894. For the next 15 years he studied Mars. He wrote books and articles about the canals and the civilisation that built them. He lectured on the subject and published maps of a vast irrigation network. But the canals turned out to be figments, chance alignments of dark patches that hopeful eyes straining through early telescopes had strung together into lines. Images of Mars from the Mariner spacecraft in the 1960s finally proved that the canals were an optical blunder. Lowell had better luck with Pluto. He used his brain, not his eyes, to deduce the existence of the distant planet. And this time he was right.