DEARBORN, MICH.- At sunset on a late summer weekend in 1924, crowds flocked to curbside telescopes to behold the advanced alien civilization they believed to be present on the surface of Mars.

“See the wonders of Mars!” an uptown sidewalk astronomer shouted in New York City on Saturday, Aug. 23. “Now is your chance to view the snowcaps and the great canals that are causing so much talk among the scientists. You’ll never have such a chance again in your lifetime.”

That weekend, Earth and Mars were separated by just 34 million miles, closer than at any other point in a century. Although this orbital alignment, called an opposition, occurs every 26 months, this one was particularly captivating to audiences across continents and inspired some of the first large-scale efforts to detect alien life.

“In scores of observatories, watchers and photographers are centering their attention on that enigmatic red disk,” journalist Silas Bent wrote on Aug. 17, 1924. He added that it might be the moment to “solve the disputed question of whether supermen rove his crust, and whether those lines, which many observers say they have seen, really are irrigation canals.”

Scientists plotted for years to make the most of the Martian “close-up.” To aid the experiments, the U.S. Navy cleared the airwaves, imposing a nationwide period of radio silence for five minutes at the top of each hour from Aug. 21 to 24 so that messages from Martians could be heard. A military cryptographer was on hand to “translate any peculiar messages that might come by radio from Mars.”

Then, lo and behold, an astonishing radio signal arrived with the opposition.

A series of dots and dashes, captured by an airborne antenna, produced a photographic record of “a crudely drawn face,” according to news reports. The tantalizing results and subsequent media frenzy inflamed the public’s imagination. It seemed as if Mars was speaking, but what was it trying to say?

“The film shows a repetition, at intervals of about a half-hour, of what appears to be a man’s face,” one of the experiment’s leaders said days later.

“It’s a freak which we can’t explain,” he added.

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A century has elapsed since the Mars mania of 1924, but the source of that strange signal remains a mystery. The original paper record is presumed lost, though digital copies have survived, ensuring that the crudely drawn face continues to stare out at us across time.

But the story of the 1924 Mars opposition is as much about the audacity of attempting a detection of extraterrestrial life as it was about the murky outcomes. Some things have changed, such as our technologies for studying the cosmos. But what endures is that sneaky feeling that we are not alone in the universe.

“We need some cosmic company out there, whether it’s in the form of gods or extraterrestrials,” said Steven Dick, an astronomer and former NASA chief historian who has written about humanity’s interest in aliens. “People go out and look at the night sky, and there’s all these thousands of stars, and they think, ‘Surely we can’t be the only ones.’”

“That’s a nice thought, but it’s not science,” he added.

The science, so far, includes the discovery that the basic building blocks of life are widely distributed in our galaxy. Researchers have also spotted thousands of planets orbiting other stars, including worlds roughly the size of Earth. And they know Mars was once habitable, a place with gushing rivers, freshwater lakes and substantive skies. They have even discovered possible biosignatures there, both from the past and in the present, although there is still no slam-dunk evidence of aliens there, or anywhere.

Humanity has learned so much about our world, and others beyond it, in a century. But that progress flowed in part from the attitudes that defined the 1924 Mars opposition as an important milestone in the history of our search for aliens — a moment when the physical proximity of two worlds exposed a deeper yearning for cosmic connection, and the will to actively seek that contact through scientific innovation, that is still very much with us today.

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In the expansive collections of the Henry Ford Museum of American Innovation near Detroit, there is a boxy artifact that was designed for the trenches and battlefields of World War I. In August 1924, it wound up serving as an interplanetary communications prototype.

Kristen Gallerneaux, a sonic historian and a curator of communication and information technology at the Henry Ford, is a caretaker of many technological relics. But they have a special fondness for the device, a Navy-type model SE 950 radio, and its historic role as a would-be alien-detector.

“It is exactly my kind of object,” Gallerneaux said. “It feels like a buried history to me.”

Manufactured on March 26, 1918, by the National Electrical Supply Co., the hardy portable radio was designed to support troops in combat, but this unit was never battle tested. It ended up, instead, in the Washington laboratory of Charles Francis Jenkins, an inventor who played a key role in the development of television.

It might have been used in many postwar experiments, but its golden hour arrived before the 1924 Mars opposition when astronomer David Peck Todd enlisted Jenkins to solve a problem that still animates the community involved in the search for extraterrestrial intelligence: If messages from intelligent aliens are wafting through space, how might we capture them?

The astronomer and the inventor cobbled together an answer. During the opposition, a dirigible was launched from the U.S. Naval Observatory in Washington to an altitude of just under 2 miles. It carried an antenna, pointed at Mars, that relayed signals back from its aerial position to the SE 950 radio in Jenkins’ lab.

The data was then fed into the inventor’s “Radio Camera,” which converted radio signals into optical flashes that left imprints on a 38-foot-long roll of photographic paper. It was this process that produced the repeating pattern that many viewers interpreted as a face.

People were “looking for the pattern of themselves in an output that was never designed to be an understandable visual representation,” Gallerneaux said. “It’s static. Yet people are still seeing things in it and experiencing it as a kind of intelligent static.”

This anthropomorphization of radio feedback may seem like a case of imagination run wild. But it makes more sense in light of claims during that historical period by many reputable experts who believed they had already uncovered evidence of intelligent beings on Mars.

“I have encountered, during my experiments with wireless telegraphy, the most amazing phenomena,” Guglielmo Marconi, a wireless radio pioneer, said in 1920, referring to signals he speculated had been “sent by the inhabitants of other planets to the inhabitants of Earth.”

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These claims helped to stoke imaginary Martians across the booming genre of science fiction. At the same time, radio emerged as a conduit for conversation with these beings.

“Our ideas about aliens ultimately stem from the way we think about our own world,” said Rebecca Charbonneau, a historian of science at the American Institute of Physics. If radios can communicate across the planet, she added, “it’s not that big of a leap to think we can use the same technology on other planets.”

People in this era were reeling from the fallout of devastating conflicts, disruptive technologies and vanishing wilderness. That provided fertile ground for visions of a civilization on the planet next door, older and wiser than our own, that might offer consolation and guidance, if only we could strike up a conversation with them.

“It is reasonable to suppose that the Martian knows much more about us than we know about him or his world, and it is interesting to speculate what he thinks of us, of our feverish struggle for a living, our vanities, our suicidal World War, our little gardens and our big deserts,” Silas Bent wrote in advance of the 1924 Mars opposition.

As some people longed for interplanetary validation, others worried about the wisdom of communicating with alien neighbors. A 1919 editorial titled “Let the Stars Alone” suggested that humans could be “unprepared” for “superior intelligences.”

Imagine if humans were to “cheerfully wireless to Mars, ‘two plus two is four,’ and Mars answers, ‘no, you’re wrong,’” the editorial posited. “What are you going to do about it?”

The opposition was an opportunity to road-test these competing ideas. From a hilltop in England, a group recorded “strange noises” that “could not be identified as coming from any earthly station.” In Vancouver, British Columbia, a signal “led radio experts here seriously to consider the theory that Mars is trying to ‘tune in.’”

Not all who peered through telescopes were impressed. “Either I’m drunk or Mars is drunk,” one sidewalk observer quipped, referring to the jostling motion of the planet through the eyepiece. “If that’s all you can show, you’re welcome to Mars as far as I’m concerned,” said another.

Ultimately, the opposition produced no lasting evidence of Martian life, a result that vindicated scientific skeptics who had spent years pointing to the red planet’s absence of water or breathable air. Such truth seekers were often mocked.

“Some great talkers conclude that Mars must be uninhabitable,” French astronomer Camille Flammarion, a firm believer in intelligent Martians, wrote in March 1924. “This is not the reasoning of philosophers, but of fish,” he continued, comparing skeptics to fish who believe life out of water is impossible.

Jenkins and Todd also embodied this duality between skeptic and believer. Todd was convinced the Jenkins Radio Camera was capable of establishing contact with alien life, and he interpreted the signals as potentially alien in origin.

“The Jenkins machine is perhaps the hypothetical Martians’ best chance of making themselves known to Earth,” Todd said in The Washington Post.

Jenkins, in contrast, was blindsided by the signal from his Radio Camera, and worried that misinterpretations of its meaning would tarnish his scientific reputation. His anxieties offer an early premonition of the shifting fault lines that the search for aliens continues to drive among academics, the media, the government and the general public, which are far more pronounced 100 years later.

“I don’t think the results have anything to do with Mars,” Jenkins said in an article published on Aug. 28, 1924. He speculated that the sounds had a banal terrestrial origin, like radio interference. Subsequent guesses have included trolley cars or natural radio emissions from Jupiter.

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Regardless of the source, the radio signals and Mars fever of August 1924 helped set the stage for more practical and scientific efforts to search for aliens.

The current hunt for extraterrestrial life stretches far beyond Mars, but the popular expectation that we will, one day, find it has proved remarkably static and durable. Indeed, many people believe we have already found aliens, or that they have found us. And even as scientists search for aliens in real physical spaces — an ancient Martian lake bed, the geysers of an ice moon and the starlit skies of exoplanets — humanity continues to dream up a mind-bending variety of fictional aliens to populate our mental landscapes.

When Jenkins and Todd conducted their experiment, radio astronomy hadn’t been born; it would be nearly a decade before Bell Labs engineer Karl Jansky stumbled upon the vast radio universe.

Today, a host of sophisticated technologies are revealing insights about the universe that nobody could have imagined 100 years ago. Rovers trundle across Mars, telescopes resolve chemicals in the clouds of faraway exoplanets and observatories scan space for messages across millions of radio frequencies.

But with regard to alien life, all of this ingenuity and investment has delivered the same basic result as that inscrutable readout of dots and dashes, mediated by a wartime radio born too late for combat, captured in 1924.

As an object, Jenkins’ radio “can exist in multiple timelines in its own way,” Gallerneaux said. “It existed and it did a certain thing back then, but we can look back on it now and see patterns of behavior.”

This article originally appeared in The New York Times.