The Canals of Mars

In 1877, Earth and Mars made an unusually close pass as the two of them went around the sun. They were still tens of millions of miles apart, but it was closer than they usually pass as they go around the track. Astronomers around the world eagerly turned their telescopes to the night sky, for the best view of Mars they'd had for many years, or would have again for many more years to come.

One of them was Giovanni Schiaparelli, and he made the most precise observations of Mars ever made up till that time. Astronomers in the 1800s actually looked through their telescopes, something they rarely get to do today. In 1877 they were just starting to use telescopes as cameras to take pictures of heavenly objects, which is what they mostly do now, but Schiaparelli did his work the older way, with his own eyes.

Mars is very tricky to observe through a powerful telescope. Earth's windy atmosphere causes a shimmering, "boiling" effect - the same effect that makes stars twinkle, but frustrating for astronomers trying to take a careful look at something. Sometimes, for just a moment, the air will go still, and a planet or star will snap into focus briefly before starting to "boil" again. Schiaparelli, working night after night, tried to make the most of these brief moments of clarity.

His efforts produced the first maps of Mars, and he gave major features of the Martian surface the names they still bear. Alas, in his efforts to trace and map things at the very edge of visiblity, Schiaparelli sometimes tried a bit too hard, and thought he saw things that weren't there. His map of Mars, in fact, does not look very much like the Mars we can see now from telescopes in space, above the boiling atmosphere, not to mention close-ups from Mars itself.

Errors like this are not surprising - Schiaparelli was like someone trying to sketch the design on a quarter from 20 feet away, when it is lying at the bottom of a swimming pool. The amazing thing is that he was able to make out anything at all on Mars from 30 million miles away. Astronomers' early efforts to map every planet produced similar wrong guesses.

Schiaparelli's mistakes, however, turned out to be magical. He saw what looked like a network of dark streaks on the surface of Mars, which he thought might be channels through which water flowed. This in itself was sensational. Even in 1877 scientists appreciated that liquid water is the stuff of life; if Mars had water channels it might have life. Indeed, some regions of Mars seemed to undergo seasonal changes, perhaps due to vegetation.

When Schiaparelli published his map and reports, however, he naturally published them in Italian. The Italian word for "channels" is canali - which to English speakers suggests canals. (In Italian it can mean either one.) "Canals" is how it got translated - and English-speakers, at least, were off to the races. Channels can be natural or artificial, but canals, like the ones in Venice, are always artificial.

If Mars had canals, then it also had Martians.

Schiaparelli's idea got taken up by American businessman turned astronomer Percival Lowell, who built Lowell Observatory in Arizona especially to observe Mars. With even more eager imagination than Schiaparelli, he elaborated on Schiaparelli's map - some canals, for example, he saw as double lines, like an enormous divided highway. With yet more imagination still, he constructed a wonderfully elegant theory about the (supposed) canals' builders.

Mars, said Lowell, was an old and slowly dying world. Its oceans were gone, leaving only lowland plains. It still had icecaps, however, that grew each Martian winter and shrank each summer. The civilized Martians had learned how to tap the icecaps, building the immense canal system to catch spring runoff as the ice melted and carry it to their irrigated croplands.

What we saw from Earth - or what Schiaparelli, Lowell, and other observers thought they were seeing - were not the canals themselves, but the broad swaths of irrigated land along each side. Living in the Southwest, Lowell had similar if smaller features before his eye. The Rio Grande and other Southwestern desert rivers have belts of irrigated land to each side. The rivers are natural, but a large canal would have the same effect.

If Mars was an ancient world, then the Martians must be an ancient civilization - and an immensely powerful and sophisticated one, capable of building a canal system across their entire world. This idea immediately caught the popular imagination, and played an enormous role in the development of science fiction. H.G. Wells' ruthless space invaders, Edgar Burrough's lovely and barely-dressed Princess Deja Thoris, and Robert Heinlein's ancient race of wise mystics, all were inspired by Lowell's vision of ancient Mars and its canals.

A good many astronomers were always skeptical of the canals, or even Schiaparelli's more neutral "channels." Hard as they tried, they just couldn't see them through their telescopes. Suspicion grew that the canals were a subtle optical illusion - if you expected to see them, you probably would think you glimpsed them, but if you weren't looking for them there was probably nothing to see.

Belief in a Mars with channels, let alone canals and a living or extinct civilization, was fading away by midcentury, and the dawn of the Space Age brought it all crashing down. In 1964 the Pioneer 4 space probe gave us our first close-ups of Mars - and showed not only no hint of canals, but a desolate, cratered world much like the Moon. Space travel had killed the dream.

Later on, space travel brought it back, at least a little bit. Later space probes showed that there are indeed channels on Mars - including Valle Marinaris, many times larger and deeper than the Grand Canyon. Most of the channels (though not Valle Marinaris) are now believed to have been carved by flowing water. Not a single one of these true ancient river or flood channels, however, is among the channels that Schiaparelli thought he saw.

Mars is indeed an old world, though no older than Earth, and it is also a slowly dying world. Its seas and rivers went dry billions of years ago, though underground ice melt still comes to the surface and flows briefly before freezing or evaporating. No one now expects to find an ancient civilization there, or Dejah Thoris, but scientists and space probes continue to look for possible signs of ancient or even surviving life on Mars.