Scientists searching for life on Mars heard a signal that hinted at future discoveries

In 1924, a radio receiver built for the battlefields of World War I tested the idea that humans were not alone in the solar system, kicking off a century of searching for extraterrestrial life.

On a late summer weekend in 1924, crowds flocked to roadside telescopes to peer at what they believed to be an advanced alien civilization on the surface of Mars.

“See the wonders of Mars!” shouted an astronomer on a New York sidewalk on Saturday, August 23. “Now is your chance to see the snow caps and great canals that scientists talk about. You will never have such a chance again in your life.”

That weekend, Earth and Mars were separated by just 54 million kilometers, closer than at any point in the last century. Although this orbital alignment, called opposition, occurs every 26 months, this event was especially exciting for viewers on all continents and inspired the first large-scale efforts to detect alien life.

“At scores of observatories, observers and photographers are concentrating their attention on this mysterious red disk,” wrote journalist Silas Bent on August 17, 1924. He added that the moment might have come “to settle the contentious question of whether supermen roam the Martian crust, and whether the lines which many observers claim to have seen are really irrigation canals.”

Scientists had been preparing for years to make the most of the Martian “close-up.” To help the experiments, the U.S. Navy cleared the airwaves, instituting a nationwide period of radio silence for five minutes at the top of each hour from August 21 to 24, so that messages from the Martians could be heard. A military cryptographer stood by to “translate any unusual messages that might come over the radio from Mars.”

And suddenly during confrontations Scientists have received an amazing radio signal from the planet.

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

“What appears to be a human face is repeated on the tape at intervals of about half an hour,” one of the experiment's leaders said a few days later. “It's a quirk we can't explain,” he added.

A century has passed since the Mars mania of 1924, but the source of that strange signal remains a mystery. The original paper recording is believed to be lost, though digital copies survive, and a crudely drawn face continues to stare back at us through time.

But the story of Mars's 1924 opposition is not just about the audacity of trying to find extraterrestrial life, it's also about the murky results. Some things have changed, like our technology for exploring space. But there remains that nagging feeling that we are not alone in the universe.

“We need space company, whether it’s gods or aliens,” says Steven Dick, an astronomer and former NASA chief historian who has written about humanity’s fascination with aliens. “People go outside and look at the night sky and there are thousands of stars, and they think, ‘Surely we can’t be alone.’”

“It's a nice thought, but it's not real science,” he added.

Science has now discovered that the basic building blocks of life are widespread throughout our galaxy. Researchers have also discovered thousands of planets orbiting other stars, including worlds about the size of Earth. They know that Mars was once habitable, with flowing rivers, freshwater lakes, and clear skies. They have even detected possible biosignatures there, both past and present, though there is still no convincing evidence of aliens there or anywhere else.

In the last century, humanity has learned so much about our world and the worlds beyond. But that progress is partly due to the attitudes that defined the 1924 Mars opposition as a major milestone in our search for extraterrestrials—a moment when the physical proximity of two worlds revealed a deeper yearning for cosmic connection and a desire to actively seek that contact through scientific innovations that are still with us today.

In the vast collections of the Henry Ford Museum of American Innovation outside Detroit is a rectangular artifact destined for the trenches and battlefields of World War I. In August 1924, it became the prototype for an interplanetary communication device.

Kristen Gallerneau, a sound historian and curator of communications and information technology at the Henry Ford Museum, has many technological relics of her own. But she has a special fondness for this device, a Navy-style SE 950 radio, and its historical role as a potential alien detector. “It’s one of those things that I love,” she says. “It’s like buried history to me.”

Released on March 26, 1918, by the National Electrical Supply Company, the rugged portable radio was intended to support troops in combat, but the device was never field-tested. Instead, it found its way to the Washington, D.C., laboratory of Charles Francis Jenkins, an inventor who played a key role in the creation of television.

The radio receiver might have been used in many postwar experiments, but its golden hour came before the Mars opposition of 1924, when astronomer David Peck Todd enlisted Mr. Jenkins to solve a problem that still vexed the SETI community: If messages from intelligent aliens were traveling through space, how could we pick them up?

An astronomer and an inventor found the answer. During the standoff, an airship was launched from the US Naval Observatory in Washington to an altitude of just under three kilometers. It carried an antenna aimed at Mars, which transmitted signals from the antenna to an SE 950 radio receiver in Mr. Jenkins' lab.

The data was then fed into the inventor's “Radio Camera,” which converted the radio signals into optical flashes that left imprints on a 12-meter-long roll of photographic paper. It was this process that resulted in the repeating pattern that many viewers mistook for a face.

According to Dr. Gallerno, people were “looking for themselves in output that was never intended to be visually represented in an understandable way.” “It’s static. But people still see something in it and perceive it as some kind of intelligent static.”

This anthropomorphization of radio signals may seem like wild imagination. But it makes sense in light of the claims made during that period by many reputable experts who believed they had already found evidence of intelligent beings on Mars.

In 1920, Guglielmo Marconi, a pioneer of wireless radio communication, stated: “During my experiments with wireless telegraphy I encountered the most astonishing phenomena,” referring to signals that he supposed were “sent from inhabitants of other planets to those of the Earth.”

These claims helped to introduce imaginary Martians into the burgeoning genre of science fiction, while radio became a channel for communicating with these beings.

“Our ideas about aliens ultimately stem from how we think about our own world,” says Rebecca Charbonneau, a historian of science at the American Institute of Physics. If radios can transmit information across the planet, she adds, “it’s not that far-fetched to think that we could use the same technology on other planets.”

The people of that era were living through the aftermath of devastating conflict, destructive technology, and the disappearance of wildlife. This provided fertile ground for imagining a civilization on a neighboring planet, older and wiser than our own, that might offer solace and guidance if only we could engage in conversation with it.

“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, our feverish struggle for life, our vanity, our suicidal world war, our little gardens and our great deserts,” wrote Silas Bent in anticipation of the 1924 opposition to Mars.

While some people yearned for interplanetary confirmation, others worried about the wisdom of communicating with their alien neighbors. A 1919 editorial titled “Let the Stars Be Alone” warned that humans might be “unprepared” to meet “higher intelligence.”

Imagine people “happily saying to Mars, ‘Two plus two is four,’ and Mars responding, ‘No, you’re wrong,’” the article said. “What would you do about that?”

The standoff provided an opportunity to test these competing ideas. From a hilltop in England, the team recorded “strange noises” that “could not be identified as coming from any Earth station.” In Vancouver, British Columbia, another signal “caused radio experts to seriously consider the theory that Mars was trying to ‘tune in.’”

Not everyone peering through the telescopes was impressed. “Either I’m drunk or Mars is drunk,” one observer remarked, referring to the planet’s twitching image in the eyepiece. “If that’s all you can show, welcome to Mars,” said another.

In the end, the standoff produced no convincing evidence of Martian life, vindicating scientific skeptics who had spent years pointing out the lack of water or breathable air on the red planet. Such truth-seekers were often ridiculed.

“Some great talkers come to the conclusion that Mars must be uninhabitable,” wrote the French astronomer Camille Flammarion, a firm believer in the existence of intelligent Martians, in March 1924. “These are not the thoughts of philosophers, but of fish,” he continued, comparing skeptics to fish who believe that life outside of water is impossible.

Mr. Jenkins and Mr. Todd also embodied this duality between sceptic and believer. Mr. Todd was convinced that Jenkins' radio camera was capable of making contact with alien life, and interpreted the signals as potentially alien in origin.

“Jenkins' spacecraft may be the best chance the hypothetical Martians have to make their mark on Earth,” Mr. Todd told The Washington Post.

Mr. Jenkins, by contrast, was stunned by the signal from his radio camera, and worried that misinterpreting its meaning would tarnish his scientific reputation. His worries are an early premonition of the shifting fault lines that the search for aliens continues to drive among scientists, the news media, government and the public, and that are much more pronounced 100 years later.

“I do not think that these results have anything to do with Mars,” Mr. Jenkins said in a paper published Aug. 28, 1924. He suggested that the sounds were of mundane terrestrial origin, such as radio interference. Subsequent suggestions included trolley buses or natural radio emissions from Jupiter.

Whatever their source, the radio signals and the Martian fever of August 1924 marked the beginning of more practical and scientific efforts to search for aliens.

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

When Mr. Jenkins and Mr. Todd conducted their experiment, radio astronomy had not yet been born; it would be nearly a decade before Bell Labs engineer Karl Jansky stumbled upon a vast radio universe.

Today, a host of sophisticated technologies are revealing information about the universe that no one could have imagined 100 years ago. Rovers plow the surface of Mars, telescopes study the chemicals in the clouds of distant exoplanets, and observatories scan the cosmos for messages on millions of radio frequencies.

But when it comes to alien life, all this ingenuity and investment has led to the same basic result as the incomprehensible reading of dots and dashes mediated by a military radio born too late for combat and captured in 1924.

As an object, Mr. Jenkins' radio “can exist in multiple timelines,” says Dr. Gallerno. “It existed and did certain things in those times, but we can look back at it now and see certain patterns of behavior.”