Sagan: Yes, I was similarly intrigued when I read the John Carter stories by Edgar Rice Burroughs. Well, the actual story on the canals appears to be that there are no lines "like those on a fine steel etching," as Percival Lowell described them. The canals seem to be a sort of psychophysiological rather than an astronomical problem. The eye tends, when the "seeing," or atmospheric turbulence is pretty bad, to string up disconnected fine detail, because it's easier to remember a straight line than a patchy, disconnected matrix of blobs. The observation of the best visual observers in the last 50 years has been that they can see canals when the seeing is bad. But as the seeing improves to the best it ever gets, they are unable to resolve the straight lines into disconnected fine detail. So even before Mariner close-up photography of Mars, most astronomers studying the subject were prepared to believe that there was not actually a network of straight lines—exceptionally straight lines crossing the planet, going for thousands of kilometers following great circle routes and so on. And indeed Mariners 4, 6, and 7 found virtually not a trace of anything at all like such canals. Now Mariner 9 is providing the first full coverage of the Martian surface, where everything has been photographed with a resolution of one kilometer except for a little cap at the very north pole.