Searching for Life Elsewhere: What We Look At, and What We Think We See

For decades, serious astronomers reported seeing lines on Mars — and some saw in them canals dug by a civilisation.

There were none.

This story is instructive because it is not about credulous people but about competent people, equipped with good instruments, who were collectively wrong.

What Schiaparelli wrote

In 1877, the Italian astronomer Giovanni Schiaparelli observed Mars and drew up a detailed map of it. The work was remarkable.¹¹

He saw long dark lines on it, and he called them canali — an Italian word meaning channels, furrows, grooves. The term implies nothing artificial.²²

What happened to the word

On its way into English, canali was translated as canals.³³

Yet in English, a canal is a work dug by human hands — unlike a channel, which can be natural. A natural feature of the landscape had thus become a feat of construction.

The time was ripe: the Suez Canal had just been cut, and it was the great feat of engineering the whole world was talking about. The word “canals” immediately called that feat to mind.⁴⁴

A wealthy American astronomer, Percival Lowell, then had an observatory built to study them. He concluded that they were irrigation canals dug by a civilisation dying of thirst, which would bring water from the polar caps to its deserts. He published several books, one of them entitled Mars and Its Canals.⁵⁵

The idea occupied people’s minds for decades.

A common version that is too simple

One often reads that “a single mistranslation changed everything”.

The formula is too neat, and historians of science present things differently.

The canals of Mars were the product of two causes acting together.

The first is the instrument. The telescopes of the time showed Mars as a small, shimmering disc, covered with faint, blurred patches. The human eye, faced with indistinct points, has an unfortunate tendency: it connects them. It manufactures lines where there are only patches.

The second is the word. Once these lines had been christened “canals”, it became impossible to see them any other way.

As for the refutation, when it came, it did not come from reasoning: it came from a better instrument. When the first probes flew past Mars in the 1960s, they sent back close-ups. There were no canals. There were craters.⁶⁶

The right formula is therefore not “the word created the illusion”, but: the word made the illusion tellable. It gave it a name, an explanation, and a story.

The most troubling part

After Schiaparelli, other astronomers began to see them, in good observatories. Not amateurs, but serious observers. Some even reported new canals, which had appeared where there had been none before.

These astronomers were not liars. They were looking at a blurred image knowing what they were supposed to find in it — and they found it.

Expectation changes what we see. This is not a character flaw: it is a property of human perception, and it affects everyone.

A hundred and twenty years later

This story is worth setting beside another, told on our page about black holes.

An international team observes a black hole with radio telescopes spread across the planet, then prepares to reconstruct its first image. These researchers have exactly Lowell’s problem: theory tells them that they ought to see a ring. The risk of manufacturing it without meaning to is enormous.

So they split into four teams that work without knowing what the others are doing, with different methods. Then they compare.

What remains to be understood is what separates the two situations.

Intelligence has nothing to do with it: Lowell and his contemporaries were not stupid. Nor does the quality of the instruments explain everything.

The difference is that, a century later, people knew the problem existed, and deliberately built a set-up capable of proving them wrong.

This is perhaps the most important lesson this site can offer about the sciences. A good method does not consist in being very clever. It consists in organising oneself in advance so that one’s own errors become visible.

The equation that was an agenda

A famous formula is supposed to calculate the number of civilisations that might exist in our galaxy. It is the Drake equation.

It was not made to calculate anything at all.

Its author himself told the story of how it came about:

“As I planned the meeting, I realized a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it’s going to be to detect extraterrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number.”⁷⁷

The last sentence is decisive. The number came afterwards: it is a by-product.

The most famous formula in the search for life elsewhere is a meeting agenda.

What the formula really does

Its seven factors are not numbers. They are seven questions, each an obstacle that would have to be overcome: how many stars are born, how many have planets, on how many life appears, and so on. Each term was an item for discussion.

Jill Tarter, who for decades led the search for signals at the SETI Institute, gives the best description of it: “it’s a wonderful way to organize our ignorance.”⁸⁸

And one of the seven became a measurement

This is the finest part of the story.

When the equation was written, not a single exoplanet was known — not a single planet outside the solar system. The proportion of stars that have them was pure conjecture.

The first planet orbiting a star similar to the Sun was detected in 1995 by Michel Mayor and Didier Queloz of the University of Geneva. They received the Nobel Prize in Physics for it. Since then, thousands have been found, and surveys indicate that there is at least one planet per star on average in our galaxy.⁹⁹

One term out of seven has gone from guesswork to measurement. That is exactly what the equation was made to produce: not an answer, but a list of things to go and look for. It worked.

Why be wary of it all the same

The strongest objection comes down to three arguments that are easy to remember. If even one of the seven values is wrongly estimated, the result is worthless. If a factor has been forgotten, it is worthless too. If one has been added that did not count, the same applies.

The lesson to remember holds far beyond astronomy:

Multiplying seven unknown numbers does not give a known number. It gives a number that looks like a result.

It is a formidable trap, because it looks like a calculation — and mathematical notation lends it an authority it does not have.

The 1977 signal

On Monday 15 August 1977, the Ohio State University radio telescope, nicknamed Big Ear, recorded a narrow, intense radio signal. Nobody noticed it that evening.¹⁰¹⁰

The next morning, the volunteer astronomer Jerry Ehman went through the previous day’s records. Line after line, the machine printed out the intensity picked up in fifty channels, in the form of digits and letters. That morning, among the usual 1s and 2s, he came across a most remarkable sequence: 6EQUJ5, in which the U denotes a signal thirty times stronger than a 1.¹¹¹¹

Beside it, he wrote a word in red ink: “Wow!”¹²¹²

The most famous signal in this whole search bears the name of an exclamation scribbled in a margin.

Two points almost always passed over in silence

First point. The signal lasted just over a minute — and that is precisely the time a fixed point in the sky takes to cross this telescope’s beam, carried along by the Earth’s rotation.¹³¹³

It could therefore have lasted longer. Perhaps much longer. We will never know, because what was measured there was the limit of the instrument as much as the phenomenon.

That said, this coincidence is also what makes the signal interesting: it rose and then fell exactly as a fixed source in the sky would, and not like interference coming from the ground.¹⁴¹⁴

Second point. It never recurred. Many observatories have pointed at that area. Nothing.¹⁵¹⁵

Explanations, proposed and debated

Several natural hypotheses have been put forward over the decades — comets passing through that spot, a hydrogen cloud whose emission is said to have been abruptly amplified. Each has been examined, debated, and contested by other researchers.

One detail deserves to be noted in passing: some of these explanations involve objects discovered long after 1977. It is impossible to explain a phenomenon by something that is not yet known. What is unexplained in one era is sometimes simply what there is not yet a vocabulary for.

Where the question stands

The SETI Institute, which has no reason to play the matter down, puts it bluntly: the question remains open. Natural source, human interference, or something else: the mystery remains.¹⁶¹⁶

Moreover, the director of the observatory at the time still maintains that the signal is of interest: the way it followed the shape of the beam indicated that it came from at least as far away as the Moon, which makes terrestrial interference very unlikely. “Efforts to re-observe it afterwards with other telescopes have been unsuccessful, so this will likely remain a perpetual mystery.”¹⁷¹⁷