Half a century ago, humans beamed a set of ones and zeros from our own tiny blue marble to a faraway group of stars, like a message in a bottle tossed into the cosmic ocean.
The code marked humanity’s first intentional interstellar transmission—a long-distance call intended for an alien audience.
Using a massive radio telescope at the Arecibo Observatory nestled in the foothills of Puerto Rico, astronomers beamed the message in the direction of a huge group of stars called Messier 13 some 25,000 light-years away from Earth.
Broadcast on November 16, 1974, the so-called Arecibo Message was the brainchild of Frank Drake—a legendary astronomer known for the eponymous Drake Equation, which estimated the probability of life beyond Earth—with input from famous science communicator Carl Sagan.
“It was the first message sent out to space, and it was beamed out from the most powerful instrument at the time,” says Abel Méndez, a planetary astrobiologist and director of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. For Méndez and others, the transmission’s legacy lives on as they try to determine where the message is today and devise new interstellar communications.
A giant ear listening to the heavens
After three years of construction, the Arecibo Observatory opened its doors in 1963. For decades, it was the most sensitive radio telescope in the world. The gigantic bowl-shaped radio dish, which was built in a natural sinkhole and included a 900-ton steel platform suspended above it, stood out starkly among verdant Puerto Rican mountains.
In 1974, newly installed equipment made the radio telescope capable of transmitting signals with twenty times the combined power of all power plants on Earth at the time. The Arecibo Message largely served a symbolic purpose: to celebrate the telescope’s new ability to peer farther into space than ever before.
The original Arecibo Message was in binary form and not color-coded. From the top down, and reading right to left, the message had seven parts: the numbers 10 to one (magenta); atomic numbers for phosphorus, oxygen, nitrogen, carbon and hydrogen (white); the chemical formulas for the sugar and bases that make up DNA nucleotides (green); the number of nucleotides in a DNA molecule (white) and the double helix structure (light blue); the population of Earth (pink), as well as the average human height (dark blue) and a human male figure (red); a solar system map showing the sun and planets (yellow); and finally the Arecibo telescope (orange) with its dimensions (grey).
Image by Science Photo Library
A team of Puerto Rican undergraduate students were selected in 2018 to create a new message, inspired by the original, with updated information about our solar system and reduced information about humans. Like the original message, this one is also written in binary code. The students proposed Teegarden’s Star as a target for the new intergalactic telegram, but so far, there are no plans to broadcast it to deep space.
Image Courtesy University of Puerto Rico
To craft the transmission, Drake enlisted the help of Cornell University graduate students. “Drake started creating the message,” Richard Isaacman, then a Cornell graduate student and now a consultant for NASA contractors, says. “He showed me what he had so far, which was fairly close to the finished product.”
The project would announce humanity’s existence in the cosmos. So Drake used a binary format, the most basic computer code, to convey some Earth essentials: our system of counting numbers, the double helix structure of DNA, where we can be found in a blocky depiction of the solar system, as well as simple drawings of a human figure and the observatory that sent the message.
Isaacman suggested making the third planet from the sun stand out from the other worlds in the solar system to indicate to any potential alien pen pals that it was the inhabited one.
The final message was broadcast for about three minutes at a frequency of 2380 megahertz and contained 1,679 bits of data arranged in a grid measuring 73 rows by 23 columns.
No read receipts
The odds of a response were miniscule, but the transmission’s impact on astronomers was huge. “This attempt has opened our minds greatly to the possibilities” of interstellar communication, says Méndez. It raised questions like, “Can other [life forms] understand us? If we’re capable of searching for signals, are other civilizations doing the same?”
After that fateful November day in the lush mountains of Arecibo, Puerto Rico, the cosmic communiqué was never repeated. Given the cluster’s distance, you can expect a reply in about 50,000 years. Astronomers aren’t holding their breath.
More legitimate efforts to communicate with off-planet pen pals will require sending the message more than once, or to more than one spot in the sky, notes Méndez. Rather than expecting a reply, the message was sent to prove we could reach out to the universe, on the off chance that an intelligent civilization has the equipment to listen to our call.
Still, the prospect of contacting life from another planet forced astronomers to consider the challenges that such an extraordinary cultural exchange would bring.
The Arecibo Message’s target is Messier 13, a globular star cluster that lies in the constellation Hercules. It is around 150 light years across, 25,000 light years away from Earth, and 12 billion years old.
Photograph by J-C Cuillandre, Canada-France-Hawaii Telescope/Science Photo Library
The risks of phoning ET
After Arecibo transmitted the message, scientists expressed concern that it had been sent out into deep space without broad consultation.
“If one were to try and create such a message today, one would certainly want to take a much more inclusive intellectual approach instead at the time. Basically, 90 percent of that message was created by a 44-year-old white guy working on his own—Frank Drake,” Isaacman says. “I think if you were to go about it in a more culturally and intellectually honest way, you would want to have a much wider range of cultural and cognitive inputs than that.”
Others warned against actively shouting out towards the cosmos, suggesting we might pose a risk to humanity by attracting the attention of less-than-friendly aliens. Works of science fiction like Cixin Liu’s literary trilogy-turned-Netflix-show 3 Body Problem also consider the possibility that broadcasting our location to alien civilization puts a target on our back. In it, characters discuss the Dark Forest theory—a speculative hypothesis where alien civilizations are like prey hiding in an ever-threatening forest. They resist the urge to blab to others out of fear of hostile interstellar neighbors.
(What if aliens exist—but they’re just hiding from us?)
Groups like the SETI Institute have since proposed international protocols for transmitting such messages. “Intentionally signaling other civilizations in the Milky Way Galaxy raises concerns from all the people of Earth, about both the message and the consequences of contact,” a group of influential scientists said in a 2015 statement. “A worldwide scientific, political and humanitarian discussion must occur before any message is sent.”
Méndez points out that though some experts think it may be foolhardy to alert eavesdropping aliens of our presence, a single radio transmission will also be competing with all the TV and radio signals we’re constantly emitting from Earth.
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The last Arecibo message
In the five decades since Arecibo first beamed the message into space, our understanding of how to find life beyond Earth has greatly changed.
Astronomers discovered the first planet beyond our solar system in 1992, and since then, they’ve found over 5,000 more exoplanets. Rocky water worlds abound: Up to 29 could be in their star’s habitable zone, meaning the region around stars where liquid water—and hence, life —could exist on the surface of planets, according to Habitable Worlds Catalog.
In this new era in the hunt for alien life, Arecibo Observatory researchers launched a competition in 2018 to compose an updated message. This time, a new generation of scientists had the tantalizing yet daunting task of summing up humanity to an extraterrestrial audience.
A team of then undergraduate students from the University of Puerto Rico at Mayaguez won the contest and took cues from the original message, using the same binary digit system and a similar schematic of the solar system as they drafted a new one. “We were inspired by the original,” says team member Kelby Palencia-Torres of Toa Alta.
To expand on the previous communication, the team also included a map that pinpoints the location of Earth within the Milky Way galaxy and highlights some of the interesting cosmic objects in our solar system, such as Saturn’s rings and our lunar companion. (Of course, they updated the solar system to exclude Pluto from the planets depicted.) The proposed transmission also features physical constants like Planck’s constant and the speed of light, as well as basic mathematical operators.
The original message included information about DNA and amino acids, which some argue could be sensitive information to disclose to potentially predatory aliens. This time around, the team kept information about humans at a minimum, only including a visual representation of humans with average height and the world’s population.
The Music of the Last Arecibo MessageAs part of the 50th anniversary celebrations, scientists decided to include a musical component as part of the new message. They worked with a Puerto Rican composer named Ángel Vázquez to create a piece titled Meraki.
Andrew Hernández, Ángel Vázquez, and the Caribbean Film Orchestra
“It was very interesting what has to be accomplished so that a message not only reaches the [chosen] destination… but also how to make the message sufficiently simple, communicate exactly what we want and how to make sure that it is not misinterpreted,” says team member Cesar Quiñones Martínez of San Sebastian.
Lizmarie Mateo Roubert from Ponce, Puerto Rico, chose the message’s destination: Teegarden’s Star, a tiny, old star only 12.5 light-years away from our sun that has two potentially life-friendly worlds. “It’s relatively close compared to other systems,” Mateo Roubert says. If aliens there decoded the message and responded promptly, we’d only wait 25 years for their reply.
Fall of an icon
The Last Arecibo Message—or “the message that was never sent,” as the team calls it—won’t be broadcast in the foreseeable future.
The Arecibo Observatory collapsed in 2020 due to decay and damage from Hurricane Maria and halted transmission plans. The National Science Foundation, which supported the site, deemed the observatory too precarious to repair. The site may never collect radio data from its giant dish, but there are plans to keep the location as a STEM-focused educational center.
(Frank Drake’s daughter reflects on the loss of the iconic Arecibo telescope.)
Scientists around the world, and especially Puerto Rican astronomers, mourned the loss of the astronomical workhorse. “When the observatory fell, one of the pillars of Puerto Rico’s science fell,” Palencia-Torres says. Like thousands of other local schoolchildren, the team members visited the observatory on field trips, which stirred their interest in science.
Arecibo was one of the only Earth-bound instruments capable of not just listening to the whispers of faraway stars’ radio signals, but sending these signals out with enough power to reach the far reaches of the cosmos. NASA’s international array of giant radio antennas may be the group’s best bet. So far, there are no set plans to beam the new message or future signals, but the team is summarizing their work in a paper posted on arXiv.org this week.
To the Last Arecibo Message team, there’s comfort in the fact that the original communication is still en route to its target, proving that the observatory’s cosmic legacy will live on long after its physical demise.
“We’re still trying to communicate with faraway beings,” Palencia-Torres adds. “We’re trying to answer the age-old question, ‘Are we alone?’”
Considering the apparent motion of celestial objects over time and the concentrated swath of sky where the original message was sent, Méndez and his colleagues estimate that “a minimum of four stars will receive the signal within the first 500 years of the message’s transmission,” he says. Gaia DR3 1328057940089589376—a star 395 light-years away—will be the first star to receive the message.
That means our “you up” message to intelligent life elsewhere in the cosmos has about 345 years to go to reach our would-be cosmic neighbors.
