Images of vast ‘canals’ rippling across the red planet inspired fears of alien ‘engineers’ and changed science forever

On 16 December 2017, The New York Times began publishing a series of investigative reports confirming what conspiracy theorists had long believed. There was a ‘secret programme’ hidden within the US Department of Defense that had investigated unidentified flying objects. From offices on the fifth floor of the Pentagon, the Advanced Aerospace Threat Identification Program (AATIP) had uncovered remarkable evidence of what it called unidentified aerial phenomena (UAP), including videos of craft resembling Tic Tac mints that moved with seemingly impossible speed and agility. Military officers soon claimed that secret programmes like the AATIP had reverse-engineered extraterrestrial technology and even recovered the bodies of aliens aboard downed spacecraft. By the early 2020s, hundreds of videos and images had come to light, some of which have still not been explained. Journalists learned that, at the very least, high-ranking military officers had been covertly discussing UFOs for decades – if only as a cover for secret weapons programmes.

It sounds like the plot of a science-fiction film. But it happened. And it’s still happening. In 2025, further video evidence was presented to Congress, showing another Tic Tac-shaped craft flying over the ocean near Yemen being targeted by a Hellfire missile fired from a drone. Incredibly, the missile appears to have bounced off the craft, which continued on its path, hurtling above the water.

But what’s odd about all this isn’t just the evidence. It’s our collective response. More than half of Americans, not to mention millions or even billions of people around the world, believe that UFOs probably confirm the existence of intelligent alien life. Yet, most of us probably don’t think much about secret Pentagon programmes or impossible craft. Isn’t that strange? At this point in a Hollywood movie, riots would be tearing through cities. Governments would be teetering on the brink of collapse. It’s why the Men in Black erase the memories of anyone who even glimpses an alien. Popular culture (and common sense) make it seem obvious that the apparent discovery of aliens, let alone a conspiracy to hide their existence, should lead to mass panic.

So, why the collective shrug? And what will happen if and when humanity really does, indisputably, encounter an extraterrestrial civilisation?

For answers, we can look to one of the strangest stories in the history of science: the 19th-century ‘discovery’ of canal-building aliens on Mars. This story isn’t widely known today and, when it is told at all, it’s usually framed as a curious delusion, shared by a small group of maverick astronomers – at least one of whom had an undiagnosed eye condition. But the event had an enormous impact on scientists and the public. It involved hundreds, perhaps thousands of astronomers, and captured the attention of millions of people.

The apparent discovery of aliens on Mars a century ago reveals that the consequences of an encounter with alien life may be less traumatic but also more far-reaching than science-fiction authors have imagined.

Indeed, in a sense, ‘aliens’ have already altered our world.

It was the summer of 1877, and Earth had an intimate date with Mars. Though these planets regularly pass each other, this time they were set to come closer than they had in decades.

Because Earth is nearer to the Sun than Mars is, it takes less time to complete a full orbit. That means that our world passes the red planet every two years – an event that humans have been witnessing for millennia. First, a dim red point of light gradually brightens until it outshines everything in the night sky, save the Moon. Then the point of light seems to move backwards as Earth wheels past, before fading again. During the peak of the event, the Sun, Earth and Mars form a straight line, with Earth in the middle and the red planet opposite us. That is why this moment is known as an ‘opposition’.

However, not all oppositions are equal. The one set to occur in 1877 would happen when Mars was also in the part of its elliptical orbit that brings it nearer to the Sun. Such ‘perihelic’ oppositions (from peri, meaning near, and helios, meaning Sun) happen just once every 15-17 years and bring Mars nearer to Earth. And in some of these oppositions, the tug of distant Jupiter’s gravity means that Mars is drawn even closer to our planet. That’s what happened in 1877, when Mars passed just 56 million kilometres from Earth (it’s more than 350 million kilometres away as I write this sentence). By the measure of cosmic distances, in 1877 the two planets were almost touching.

New telescope designs allowed observers to see genuine features on the Martian surface

Changes in astronomy and in the instruments used by astronomers ensured that this opposition would truly be like no other in history. The invention of the telescope in the early 17th century had already revealed that Mars was a world, not just a point of light. Indeed, in an age of colonial expansion, Mars seemed like a new world that could be explored and charted by Europeans, remotely of course, as though it were just another imperial frontier.

By the end of the 18th century, new telescope designs allowed observers to see genuine features on the Martian surface. Astronomers had previously focused on making precise calculations of celestial movements, but now the environments of other worlds seemed worthy of serious study. What was on the surface of our neighbouring planet?

Observers soon determined that there were bright regions at the poles of Mars and dark patches at lower latitudes. What’s more, the shape and colour of these regions seemed to fluctuate dramatically over time.

Polar exploration on Earth suggested that the bright regions of Mars were ice caps undergoing seasonal melting and refreezing. The dark regions were more mysterious. These areas appeared to transform so much that early 19th-century scientists believed they had to be either cloud formations, oceans spilling their banks, or vegetation undergoing seasonal changes. Mars seemed to be a living world, much like our own.

Night after night, he huddled over his gleaming refractor, high up on a rooftop above Milan, sketching Mars

This widely held view made the opposition of 1877 a major event for scientists. Telescopes were now so powerful that it seemed like a second Earth could be unveiled for the first time during the passing of Mars.

Months before the opposition, as the red planet began to brighten in the night sky, the Italian astronomer and hydraulic engineer Giovanni Schiaparelli got to work. Night after night, he huddled over the eyepiece of his gleaming refractor, high up on a rooftop above Milan, sketching Mars. As the planet wheeled closer and closer, he recorded each new detail that shimmered into view. When the opposition passed, Schiaparelli gathered his sketches and drew a complete map of Mars in the Mercator projection – the same projection commonly used in maps of Earth’s continents.

It was like no other depiction. Astronomers had previously glimpsed linear features on the planet, but Schiaparelli’s Mars was covered with them. They were, he wrote, canali that linked Martian oceans. Schiaparelli seems to have preferred that canali would be translated as ‘channels’. However, it was more often rendered as ‘canals’ when his observations were reported in English.

Some astronomers doubted that the channels, or canals, actually existed. But Schiaparelli was a leader in his field, with renowned eyesight, and it couldn’t be denied that his map of Mars was more detailed than any drawn before. Indeed, it included so many previously uncharted features that Schiaparelli introduced a new naming scheme, drawing from classical mythology, to make sense of them all. With a decidedly alien surface named after gods and goddesses, Mars became a more mysterious and intriguing world than anyone had imagined.

In a different time, Schiaparelli’s ‘canals’ might have been a short-lived curiosity. Instead, they became a popular sensation – thanks to the shifting nature of mass media, during an age of imperial expansion and technological disruption.

Around the time of the 1877 opposition, major newspapers, such as The New York Herald, were beginning to secure exclusive access to telegraph lines that permitted instantaneous communication between far-flung cities. These newspapers did not just report what had happened along the exotic frontiers of the era’s empires. They also helped to create the news. In the process, they influenced how scientific discoveries reached ordinary people and shaped what counted as a ‘discovery’ among scientists.

These dynamics were primarily responsible for the ‘Mars Boom’ of 1892, during another perihelic opposition.

A key figure behind the boom was William Pickering, an ambitious young astronomer at Harvard College Observatory in Boston. Pickering accepted that Schiaparelli’s canals were real. He also believed that Mars was a world like Earth. The canals, he thought, were nothing more than strips of vegetation. But to know for certain, Pickering would need to take a closer look.

The canals seemed to copy themselves, or ‘germinate’, as Mars approached Earth

In 1891, he was sent to Peru by the observatory’s director (his brother, Edward) with orders to set up a modest mountaintop facility that would gather precise data about the colour and brightness of southern hemisphere stars.

Pickering did nothing of the sort.

It had been almost 15 years since the opposition of 1877, and Earth was once again bearing down on Mars. The tilt of Earth’s axis meant that when Mars reached opposition, it would be far easier to see in the southern hemisphere than in the north. With that in mind, Pickering spent lavishly to establish an observatory that would give him the best views of Mars that any astronomer had ever had. And he agreed to report what he saw to The New York Herald using a telegraph controlled by the newspaper. It was a chance for Pickering to make his name – and for the Herald to transform a planetary opposition into a sensational news event.

In 1892, as Earth approached Mars, Pickering started to send curt descriptions of his observations to the Herald. The historian of science Joshua Nall showed in News from Mars (2019) that the newspaper reworded these descriptions into a vivid narrative that played on the expectations of readers in a colonial era. The Herald presented Pickering as an explorer who had journeyed to Earth’s ends in search of a once-in-a-lifetime opportunity to discover a new world.

Pickering’s reworded descriptions included dramatic accounts of environments on Mars that embarrassed more experienced astronomers who had downplayed the scientific value of the coming opposition. One of those experts was Edward Holden, the director of the greatest observatory in the northern hemisphere: the Lick Observatory in California. Holden’s views now seemed not only foolish, but an indictment of his observatory.

In the face of popular ridicule, Holden announced to the Associated Press that he had also put the opposition to good use. Peering through the Lick telescope, he had confirmed a remarkable property of the planet’s canals, earlier suggested by Schiaparelli: they seemed to copy themselves, or ‘germinate’, as Mars approached Earth.

Holden privately doubted that the canals were real. But in the process of defending his reputation, he had introduced millions of people to the idea that the canals existed – and that they behaved like nothing else in nature. An explosion of popular interest in the canals followed, reflected by a wave of newspaper reports in the United States and Europe.

The Lick Observatory, built between 1876 and 1887, was named after the land baron James Lick, one of California’s richest men. As he neared the end of his life, Lick considered how to preserve his legacy. He toyed with building a colossal pyramid, but ultimately decided to finance the construction of a telescope big enough to detect aliens on the Moon. That discovery, he thought, would let his name ring through the ages.

In the 1890s, history began to repeat itself. Another wealthy man – Percival Lowell, heir to a fortune gained in the textile trade – saw his chance to achieve immortality. Lowell seems to have decided that if Schiaparelli had been the Columbus of Mars, discovering a new world, then he would follow in the footsteps of the Conquistadors by realising that world’s true potential. He would discover what the canals really were.

Lowell ordered a gigantic telescope from Alvan Clark & Sons, one of the world’s leading manufacturers of fine optics. But that wasn’t enough – he also needed an ideal location to install the device. In Peru, Pickering had worked out a method for measuring the suitability of the atmosphere for astronomy. Under Lowell’s direction, Pickering’s former assistant, Andrew Ellicott Douglass, used the method to identify a perfect site to build an observatory for the new telescope: Flagstaff, Arizona, where thin, dry air would permit unrivalled observations of Mars.

What was this strange, fluctuating latticework that seemed to cover the planet?

As Earth approached Mars in 1894, Lowell, Douglass and other members of their team began to observe the canals. With painstaking diligence, they would eventually map more than 400, of which more than 50 canals seemed to show signs of ‘germination’, or doubling. What’s more, the team charted some 200 oases – circular features at the intersection of canals – including one that seemed to connect no fewer than 17 canals. Nor were these features stable. They were faint when Earth approached Mars, but darkened as Earth left Mars behind.

What was this strange, fluctuating latticework that seemed to cover the planet? To Lowell, the age of Mars provided the first clue. Most scientists believed that the planets had formed one after another, from rings of gas and dust released by the Sun. That meant that Mars was older than Earth.

A second clue came from naturalists who had discovered fossilised sea creatures on dry land, far from the ocean. Earth, it seemed, was drying as it aged. When Douglass spotted a canal crisscrossing one of the dark regions of Mars, he believed he had uncovered proof that those regions weren’t oceans, as Schiaparelli and other astronomers had assumed. Because Mars was older than Earth, it was naturally drier.

A third clue came from the changes that swept across Mars. The canals seemed to darken, first around the pole and then towards the equator, as spring arrived in each Martian hemisphere. At the same time, what appeared to be an ‘ice cap’ in the northern hemisphere seemed to melt, creating a dark region around its perimeter.

A fourth clue consisted of environmental changes happening on Earth. Between 1877 and 1894 – from the time when Schiaparelli first mapped the canals to when Lowell arrived in Flagstaff – a series of extreme El Niño events brought catastrophic droughts and famine to much of the world. By then, irrigation systems and especially ship canals had emerged as quintessential infrastructure projects of an industrialising world. In the US alone, workers had built some 6,800 kilometres of navigable canals by 1860, a figure almost exactly equivalent to the diameter of Mars.

People believed they could actually see the canals using small telescopes

Lowell put the clues together. An alien civilisation, he speculated, had long ago emerged on Mars. When the planet dried out, that civilisation was imperilled. It responded by using its advanced technology to build a world-straddling network of canals. The canals funnelled water from its last reservoirs – the poles – to vast food-growing regions around the equator. When the ice caps melted in the spring, the water would flow south, and vegetation would sprout around the canals, appearing to darken them in a wave that swept from each pole to the equator. Around the north pole, a sea of meltwater formed first, creating the dark region that emerged every spring.

It was an elegant explanation, and it made Lowell an overnight celebrity. His books were bestsellers, his lectures sold out, and his ideas routinely made the front page of major newspapers. What’s more, people believed that they could actually see the canals using small telescopes, which had recently become a common possession for well-to-do families. Newspapers even printed instructions for canal-watching.

Not everyone believed Lowell’s explanation. Some astronomers always doubted that the canals were real – a view that gained credibility in the early 20th century, when powerful telescopes seemed to resolve apparently linear features on Mars into discontinuous spots and streaks. Then, in the 1960s, the robotic exploration of the planet finally proved beyond doubt that the canals were illusions, and that the environmental changes Lowell took for proof of flowing water had been caused by enormous dust storms that exposed or obscured dark rock and sand. In a sense, Mars is an even less Earth-like world than Lowell had imagined.

At the end of the 19th century, however, millions seem to have believed that a species much older and more advanced than humanity had found a way to survive on a dying planet that, every two years, passed precariously close to Earth.

In 1895, a front-page article in The Cook County Herald, an Illinois newspaper, announced that ‘very strange and mysterious things are going on on Mars.’ Douglass had just spotted what seemed like flashes along the Martian ‘terminator’, the dividing line between night and day on the planet. When he and other astronomers announced such sightings, their descriptions routinely made it into the newspapers – and prompted letters from anxious readers who believed that the Martians were messaging Earth.

Lowell uncharacteristically pointed out that the flashes were probably natural in origin, caused by sunlight glinting off ice, for example. Yet light seemed like a natural way to send a signal between worlds. Public figures of all stripes, from inventors to poets, now proposed ambitious schemes to message the Martians using light and colour.

Some called for the construction of enormous mirrors that could focus sunlight – or better yet, electric light – into beams bright enough for the Martians to see. Others suggested that immense geometric shapes could be carved into forests using fire, or that enormous strips of black fabric could be hooked to motors in the Saharan desert and rearranged to send a message. Everyone agreed that any message had to relay information universal to all intelligent life. If sent to clever Martian observers, flashes of light would communicate something about the structure of the solar system, or the basics of geometry. Once the Martians understood how humans used light flashes to communicate universal information, they would be able to respond in kind. Eventually, a shared, interplanetary language could be developed. This became the underlying principle that still informs how we think about communicating with aliens.

At the turn of the 20th century, breakthroughs in wireless communication, using radio waves, suggested light and colour weren’t the only ways to send and receive messages from Mars. Sitting in his laboratory in Colorado Springs one night in July 1899, the inventor Nikola Tesla suddenly heard a repeating radio signal that he believed might have come from another world. He was awestruck, thinking that he had witnessed ‘the revelation of a great truth’. For the rest of his life, he obsessed over how he could use his inventions to return the message. In all probability, he had actually heard a signal from Jupiter, caused by interactions between the planet’s magnetic field and the volcanoes of its moon, Io. Though the signal he received was not a real message from an alien transmitter, radio waves would become central to the search for extraterrestrial intelligence in the 20th century.

When another opposition with Mars was set to occur in 1924, most astronomers no longer accepted that idea of Martian canals. Still, many people continued to believe that the planet could harbour an alien civilisation. From 21-24 August, during the opposition, radio operators across Europe and the Americas observed a ‘National Radio Silence’ for five minutes at the top of every hour to listen for possible signals from Mars. At 7:12 am, operators at Point Grey Wireless Station in Vancouver even reported hearing a repeating pattern that briefly seemed like the message from Mars that everyone had been hoping for. The news made headlines, but the signal was soon traced to a terrestrial source.

Mars was silent. Nevertheless, it seemed as though the ‘Martians’ had communicated a grand truth. They had revealed, according to Lowell, that the ‘true history of man has consisted not in his squabbles with his kind’ but rather our species’ growing dominance over all other life. The canals suggested that the fate of all intelligent life was to remake its home world in order to delay extinction as the climate of that world dried out.

This was a forerunner to what we might now call the Anthropocene concept: the idea that humanity has remade Earth, and that this remaking is central to the history of our time. As Lowell put it, the discovery of megastructures on Mars helped to explain and justify why, even in the 19th century, ‘man has begun to leave his mark on this his globe in deforestation, in canalisation, in communication.’ Those Martian feats of planetary engineering hinted at humankind’s longer future: ‘[T]he time is coming when the earth will bear his imprint, and his alone. What he chooses, will survive; what he pleases, will lapse, and the landscape itself will become the carved object of his handiwork.’

An intelligent species did not need to go meekly into the night when facing a planetary threat

Yet the canals of Mars also hinted that the lifespan of intelligent species had a natural conclusion. Indeed, the apparent discovery of the Martians provided one of the first indications that humanity faced existential risks, meaning risks to its continued existence, and that these risks could come from changes to Earth’s climate. Mars was drying out, and the process would continue until the Martians could no longer siphon water from the poles. After that point, it seemed that every Martian would inevitably die.

Still, the beings on Mars had also shown that an intelligent species did not need to go meekly into the night when it faced a planetary threat. For some, that lesson sparked a very different kind of existential dread.

The Martians had created ‘a shadow and a fear’, the president of the Royal Astronomical Society of Canada told an audience in 1897. It seemed logical, he said, that they would look enviously at the watery Earth. Indeed, if space travel was possible, then there was no reason for the Martians to accept their fate on a drying world. They might instead take over Earth – at humanity’s expense.

The English science-fiction author H G Wells played on these fears to reimagine the lights reported on Mars as flares created by the launch of projectiles headed for Earth, heralding the invasion of our planet by ‘intellects vast and cool and unsympathetic’. His novel The War of the Worlds (1898) popularised the alien-invasion genre in science fiction but it was, above all, a critique of British colonialism. The story resonated with particular force in the anxious years before the First World War. For more than two decades after it was published, newspapers speculated about a Martian invasion whenever the planet reached opposition. Radio broadcasts of The War of the Worlds would later spark widespread panic about the possibility of a real invasion – and concerns over the compatibility of mass media with democracy. To Wells and other authors, the Martian threat exposed the folly of imperial aggression.

The Martians also seemed to reveal which social structures allowed a civilisation to reach old age. For some scholars and writers, the canals vindicated social Darwinists who used the concept of natural selection or ‘survival of the fittest’ to justify both colonialism and capitalism. Lowell believed that the stronger Martians had survived to reengineer their planet, while the weak had perished. Schiaparelli, by contrast, thought the canals were a triumph of collective socialism, a whole-of-society response to a planetary catastrophe.

In the decades after the great perihelic opposition of 1877 – through years marked by the emergence of the labour movement, the rise of communist insurgencies, the global spread of unregulated capitalism, and the eruption of imperial wars – the canal-builders on Mars seemed to have urgent lessons to impart. But what those lessons were, exactly, remained in the eye of the beholder. Some hoped that establishing contact with our Martian neighbours might change humankind. When that happened, ‘we may tell the Martians all about our great war,’ reflected an article in Popular Science in 1919; ‘perhaps we will learn from an older and wiser planet how we ought to run the Earth.’

Around the same time that alien engineers on Mars were being imagined, naturalists and explorers from imperial cities, like London or Paris, were enthralling their readers with tales of exotic lands and peoples on Earth. The Martians therefore also had a romantic, almost orientalist appeal. Novelists would later pioneer world-building science fiction by imagining adventures on a canal-covered planet with alien cultures and ecosystems.

The quest to map the canals of Mars directly expanded the frontiers of science

Few were more successful than Edgar Rice Burroughs, whose Barsoom series, beginning with A Princess of Mars (first serialised in 1912), inspired a generation of young readers. Some of those readers would play pivotal roles in the coming age of space travel. A map of the canal-covered Mars imagined by Burroughs, for example, adorned the office door of the planetary scientist Carl Sagan, a leading figure in the Viking missions that undertook the first tests for microbial life on Mars.

Indeed, the quest to map the canals of Mars directly expanded the frontiers of science. It helped establish the importance of a thin and steady atmosphere for astronomy, leading in a roundabout way to the construction of today’s mountaintop observatories. Douglass, who had compared the climate of different sites in Arizona for Lowell’s observatory, eventually decided to study the changing climate of Earth using the growth rings in trees. He would play a central role in the development of palaeoclimatology, the science of past climate change.

By revealing that climatic changes have undermined the foundations of historical societies, and by showing the deep connection between greenhouse gases and global temperature, palaeoclimatology has confirmed the essential truth of the canal theory: climate change can accompany the maturation of a technologically advanced civilisation, and can also threaten the destruction of that civilisation.

In short, the ‘discovery’ of the Martians had profound consequences – many of which continue to shape culture and science. After all, what are Star Wars’ Tatooine and Frank Herbert’s Dune if not variants of Lowell’s Mars?

The history of the canals on Mars upends two enduring assumptions. For decades, these assumptions have appeared in everything from classified government reports to Hollywood blockbusters.

The first assumption is related to how the discovery of an extraterrestrial civilisation would be made and shared. It’s easy to assume that such a discovery would happen when scientists find definitive proof, either by observing a distant planet or receiving a signal from such a planet. Major news outlets would then report the news. But science doesn’t happen in a vacuum, and news is not a transparent reflection of reality. The Martian canal sensation – one of the first examples of scientists ‘discovering’ alien life beyond our planet – was a consequence of everything from environmental changes on Earth and Mars to the transformation of mass media in an age of global imperialism.

It’s no surprise that alien news today does not involve the careful evaluation of scientific evidence

The second assumption is that the discovery of an alien civilisation would destabilise society. The canal-builders of Mars did provoke widespread unease and even spasms of local panic, especially during radio broadcasts of The War of the Worlds. But, for the most part, public order received no serious challenge. The aliens on Mars were big news, but not as big as stories about political intrigue, economic trends or the descent to war – stories that had more tangible impacts on people’s lives.

So, maybe we shouldn’t be startled at our collective shrug when new reports of UAPs surface. Nor should it surprise us that alien news today does not involve the careful evaluation of scientific evidence. Instead, it is a reflection of cultural and technological changes, such as the spread of conspiracy theories on social media, for example, or the commercialisation of drones that resemble UAPs.

The Martian canals controversy has one more lesson to offer. When the canals were eventually exposed for the illusions that they were, the reputation of planetary astronomy briefly collapsed. Today, Lowell is often remembered as a misguided maverick, rather than a serious figure in the history of science. Yet few theories have stimulated as much thought, or been as enduring and productive for culture and science, as the canals of Mars.

Astrobiology, the science that explores how life begins, survives and evolves in the Universe, is today a burgeoning discipline. Two organisations – the SETI Institute and Breakthrough Listen – now lead unprecedented efforts to contact, or at least detect, an extraterrestrial civilisation. Even if their work uncovers nothing, the history of the canals on Mars reveals that there are few enterprises more worth pursuing.