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40 Years Ago, Earth Beamed Its First Postcard to the Stars

Forty years ago, on Nov. 16, 1974, Earth beamed its first postcard to the stars.

The message left our home planet on a warm and sticky day in Puerto Rico and has been flying through the galaxy at the speed of light ever since. In about 25,000 years, it will collide with a cluster of more than 300,000 stars.

Unlike the radio signals that had been leaking from Earth since the late 1930s, this postcard was the first deliberate transmission to an alien civilization. Meant to be decipherable by extraterrestrial beings, the message contained some key information about the species that had sent it.

“It was a message that would actually inform anyone who did receive it that we existed, and tell them a little bit about what we were like,” says my dad Frank, who had the responsibility of constructing and sending what’s now known as the Arecibo Message. “And it was also a message to ourselves in that it showed what an intelligent civilization can do to contact other civilizations.”

Dad had been given just one month to write Earth’s first radio greeting to the stars.

It was 1974, and the Arecibo Observatory’s giant radio telescope had just gotten a major upgrade. Beamed into space by the Observatory’s powerful, one million-watt transmitter, the message would cap a ceremony marking the completion of the improvements (you can listen to it being sent, below). But it was a secret – only the ceremony’s organizers knew ahead of time what would happen, and they envisioned a transmission lasting about 3 minutes.

So, it needed to be relatively simple.

Texting Aliens

Fortunately, Dad had been thinking about how to write postcards to aliens for a while. Sending a message to other worlds, while simple in principle, becomes almost impossibly complex when it’s time to actually write the letter. Aside from the question of what to say, there’s the issue of how to say it.

For starters, not just any language will work – think about how difficult it is to understand the many languages spoken on Planet Earth. The chances of an alien civilization understanding, “Hi, we live on Earth and are friendly,” are vanishingly small, just like your chances of understanding “Vie minut johtajanne luo” are practically zero unless you speak Finnish. Numbers and equations, while more concrete, are still written using arbitrary symbols. And things like distance measurements are just as arbitrary as words.

So how does one compose a missive with the best chance of being universally understood?

“From day one, I’ve always thought pictures work,” Dad says. “Sending pictures is easy. We do that all the time, with great results.”

Black and White

Dad set up a grid and drew crude shapes and symbols by shading in squares. A 3-minute transmission at 10 bits of information per second meant he had at most 1,800 squares to play with.

The Arecibo Message, with colors added to identify the various components. (norro)
The Arecibo Message, with colors added to identify the various components. (norro)
His pencil traced the shapes of the numbers one through 10, in binary code. It encoded a representation of five chemical elements essential for life on Earth (hydrogen, oxygen, nitrogen, phosphorus and carbon), which he then used to draw the sugars, bases, and backbone that form life’s genetic instructions.

Then, he drew a depiction of double helical DNA, wrapped around “3 billion” written in binary code. This is the approximate number of characters (“base-pairs”) in a human genetic sequence. Below that, he shaded a human into the message, with “14” on one side, and “4 billion” on the other. The first number represented the height of an average human, in units of 12.6 centimeters – the length of the radio waves used to send the message.

The second number? In the 1970s, that was the human population of Earth.

Next came a map of the solar system (which included Pluto, since it was still one of the nine classical planets), with the Earth offset from the others, toward the human, to signal that this was our home planet. And lastly, he sketched a representation of the Arecibo telescope itself, with its size noted in units of radio wavelengths, to indicate the level of technology used to post the letter.

Sending the message would mean translating the grid into binary code, where zeros and ones denoted which squares were shaded and which were open (black squares = 1, white = 0). To decode the message, recipients would need to figure out how to organize that string of numbers into a grid with the correct dimensions, recognize that the grid contained symbols, and then decipher the meaning of those symbols. The finished message had 1,679 bits; 1679 is the product of prime numbers 23 and 73, which offers a hint about how to lay out the grid.

Test Transmission

Dad tested his message by sending it to his friend and colleague Carl Sagan, who hadn’t been involved in writing it and had no knowledge of its content. He wanted to see if Carl could figure out what was in there.

“And more importantly,” Dad adds, “Make sure he would not find things in it that were equally plausible decryptions but were wrong, which would be misleading and give inaccurate depictions of our civilization.”

Perhaps not surprisingly, Carl got almost everything right, and quickly. But the chemistry eluded him, Dad recalls, adding that biochemists he sent it to later got that part almost immediately. “People recognize things that are in the area in which they have expertise,” he says.

To Hercules

And then it was time to choose a destination.

Sitting in a sinkhole, the Arecibo telescope is somewhat limited in its steering ability. So the postcard needed to be addressed to somewhere roughly over Arecibo at 1pm on November 16, 1974, the time of the ceremony.

The heart of M13, the Great Cluster in Hercules. (ESA/Hubble and NASA)
The heart of M13, the Great Cluster in Hercules. (ESA/Hubble and NASA)

Scouring the star charts, Dad identified a worthy target: M13, the Great Cluster in Hercules. With more than 300,000 stars – and probably at least that many planets! – M13 was perfect, and its heart would fit entirely in the telescope’s beam. An Arecibo-type receiver on any of those worlds should have no trouble detecting the message. (Some people, Dad notes, think the cluster will have moved in 20,000 years, and that the message will miss it. That’s not true, he says. “It will have moved a little bit, but only a fraction of the width of the beam of transmission,” he says.)


At 1pm, just as planned, the Arecibo transmitter came to life. For a few moments, a smooth tone filled the crags and valleys of the surrounding jungle terrain.

And then the transmitter began to sing a series of alternating tones. “It sounded like a bird warbling,” Dad recalls. Over nearly three minutes, the 1,679 bits of information hurtled into space, carrying this message from Earth – the first deliberate radio transmission from the humans on our little blue planet – to whatever beings might live in that great cluster in Hercules.

“When we sent the last character, and it stopped and we went back to that steady tone, everybody was crying,” Dad says. “We were hearing what it would be like to actually contact another world. That was what that sound was. It had the aura of human beings doing something marvelous that involved the whole cosmos.”

But there was another surprise to come. Unintentionally, Dad had coded another dimension into the message. As the transmitter began to send those alternating tones, one of the engineers in the control room recognized a bit of Morse code. Hiding in the first notes of the warble was the simplest greeting of all:


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Why There’s No Place Like Home

Dad pulls a scroll of paper from one of the dozens of crumpling boxes stacked in a chilly warehouse near Santa Cruz, Calif. He gently unrolls it, and a familiar reddish ink pattern appears on the delicate grid.

“Ah,” he says. “This is Ozma.”

His fingertip traces the inky magenta line, and he squints at the faded, penciled-in numbers inscribed near the line’s peaks and valleys. “Is that your handwriting?” I ask. It doesn’t look anything like his. “Nope,” he answers. “It must be the telescope operator’s.”

The scroll my father, Frank Drake, is holding is more than a half-century old. It’s part of the data he collected during an experiment known as Project Ozma. Named after a character in L. Frank Baum’s Oz series, the project was the first scientific search for extraterrestrial intelligent life. From April to July, 1960, astronomers in Green Bank, West Virginia monitored two nearby, sun-like stars for artificial radio signals—signs that an interstellar intelligence inhabited Earth’s starry skies, that humans were not adrift in an incessantly quiet cosmic ocean.

The entire endeavor cost $2,000.

Frank Drake retrieves a scroll with data on it from Project Ozma. (Nadia Drake)
Frank Drake retrieves a scroll with data on it from Project Ozma. (Nadia Drake)

Dad was in charge; at just 29 years old, he had been planning and building the necessary equipment for the last year and half. He’d determined that the Green Bank telescope should be able to detect radio transmissions coming from up to 10 light-years away, if they were at least as strong as Earth’s. So he selected two nearby stars, Tau Ceti and Epsilon Eridani, to aim the telescope at. He built antennas and receivers and amplifiers, and picked a band of radio frequencies to monitor. He came up with a plan to follow if a signal were detected.

“For all we knew at the time, almost every star had strong radio signals coming from it,” he says. “We might look at only a few stars and succeed.”

Finally, before dawn on a chilly West Virginia morning, Dad climbed up the observatory’s 85-foot telescope, fiddled with a finicky signal amplifier, and kicked off an experiment that would ignite decades of scientific discourse about extraterrestrial civilizations. Over the next four months, dozens of scrolls like the one we were staring at would come rolling out of the pen-and-ink data recorder, each bearing a bright red record of radio static from the universe.

Of course, in the end, Tau Ceti and Epsilon Eridani showed no signs of hosting intelligent life. “That was a disappointment,” Dad says. “But as time went on, we began to realize that’s the way the universe is, and it’s not our fault.”

The search is far from over. Increasingly, we’re finding that the ingredients necessary for life on Earth are abundant in the cosmos. Water, organic molecules, and even amino acids—so basic to life as we know it—have been found in space.

And the Milky Way, our home galaxy, is stuffed with planets. Even Project Ozma’s target stars have them. “Planets are plentiful,” astrophysicist Neil DeGrasse Tyson confidently stated last night in the first episode of Cosmos: A Spacetime Odyssey, which shows again tonight on the National Geographic Channel. “They outnumber the stars.”

It’s kind of crazy to think that when Dad was collecting the Ozma data, we knew nothing about the abundance of exoplanets—in fact, it would be another three decades before the first exoplanets were reported. Pulsars were still waiting in the wings, and the moon bore no human footprints. It was a different era in astronomy, and though Project Ozma garnered a ton of media attention, thinking about life outside the solar system was still on the fringes of traditional science. But momentum was gathering.

A newspaper story that ran shortly after Ozma. (Photograph by Nadia Drake)
A newspaper story that ran shortly after Project Ozma. (Photograph by Nadia Drake)

The next year, in 1961, dad would organize a conference at Green Bank devoted to thinking about intelligent life in the universe. It was the day before that meeting that the Drake Equation, which estimates the number of detectable intelligent civilizations in the Milky Way galaxy, would be born.

But that’s a story for another time.

We’d been rummaging through piles of my father’s papers for about an hour before the first signs of Ozma casually surfaced. Before that, we’d found a map he’d made of the galactic center. Another box held data he’d used to determine the temperature on the surface of Venus—an experiment that brought him into contact with a Ph.D. student at the University of Chicago named Carl Sagan. Another box held the results of an experiment he and Sagan would conduct at the Arecibo Observatory in the late 1970s, where they surveyed nearby galaxies for intensely bright radio transmissions. And another box has memos from the Voyager record project.

In short, these sagging boxes are filled with the evidence of a life spent exploring the cosmos. It’s this adventurous ideal that led Dad to name the first SETI search after Princess Ozma. “Oz is a land, a strange land, populated by strange and exotic creatures. Which described the sort of place I was about to search for,” he says to me, later. “If we find life out there, it’s going to be much more unearth-like than Oz.”

Nadia and Frank Drake. (Photograph courtesy Nadia Drake)
Nadia and Frank Drake.

And it’s these threads of thought that led me to the name of this blog: No Place Like Home. There are infinite worlds out there, and none of them will be exactly like ours. For millennia, humans have stared at the stars and mapped the movements of heavenly bodies, seeking to learn the mathematical language and physical laws that tell the stories of the spheres. In the last half-century, we’ve managed to launch our robotic creations from Earth’s watery shores and land them on other worlds. Maybe someday, we’ll be going along for the ride as well.

For now, though, we have the science of astronomy and the spaceships of our imagination to show us what else is out there. I’m so excited to be joining National Geographic as a space blogger for Phenomena—just as Cosmos kicks off—and am thrilled to be bringing you tales from beyond our home planet.

When two hours have gone by, it’s time to go home. We carry our folding chairs and lanterns from the warehouse and step into the sunlight. Dad pauses. “After looking at all that stuff,” he says, “For a moment I didn’t know where I was. It feels weird being in California.”