What if aliens in the universe send a message to Earth, and we can’t understand what they’re saying? Communicating with another species is likely to be tricky, given how difficult it already is for humans from one culture and language to be understood by those from another. So how much harder might it be to bridge the gap between us and creatures whose bodies, minds and habitats are completely foreign to ours?

To ponder the question and practice decoding an extraterrestrial epistle, an artist-led team has created a mock message from the stars to test us Earthlings. On May 24 the ExoMars Trace Gas Orbiter beamed the note from Mars toward Earth. Three observatories detected the transmission 16 minutes later: the Medicina Radio Observatory in Bologna, Italy; the Allen Telescope Array in northern California; and the Robert C. Byrd Green Bank Telescope in West Virginia. The message, though written for humans by humans, was as nonanthropocentric as one could hope for, perhaps the most alien missive the world had ever received.

This interplanetary art project, called A Sign in Space, is an ongoing experiment: for all of humanity’s hopes for detecting technosignatures, do we have the chops to make sense of them? So far no one has deciphered the May 24 message, but many are on the case.

A Cosmic Letter

Only three people in the world know what A Sign in Space’s message means. First among them is Daniela de Paulis, the project’s founder and an artist in residence at the SETI Institute (SETI stands for the search for extraterrestrial intelligence) and the Green Bank Observatory. She and two other co-authors penned the faux alien missive after consulting with poets, scientists, programmers and philosophers.

Right away, de Paulis recognized the project’s out-of-this-world dilemma: How could her team shed its anthropocentricity to craft a message that seemed as realistically alien as possible? The challenge wasn’t just to think like an extraterrestrial but also to jettison Earth’s regional biases. Her team immediately ruled out language-based communication, though she won’t confirm or deny whether the message contains any text. Her team even agonized over using mathematics—although the fundamental concepts are universal, different societies may think about and represent math differently. Composing the message and choosing the right format gave de Paulis massive writer’s block. “It was really very heavy work to dismantle our Western-centric thinking,” she says.

De Paulis struggled with the message for years after she conceived the project in 2019. A breakthrough came in late 2022 when she contacted artist and computer programmer Giacomo Miceli, inadvertently recruiting the second author for the message. A month before the transmission deadline, astronomer Roy Smits joined the pair, adding a mathematical touch to make the message “more universal, so to speak,” de Paulis says—and much harder to crack because it looks nothing like what humans use in our daily conversations.

People have constructed communiqués meant for extraterrestrials in the past. In 1974 scientists blared a radio message into the universe using the Arecibo Telescope in Puerto Rico. The interstellar postcard—a 1,679 string of 1’s and 0’s that, when translated graphically, consisted of crude representations of a human, the Arecibo Telescope’s dish and the DNA double helix, among others—was more symbolic than a genuine attempt to hail beings in space. The likelihood of this “Arecibo message” ever being understood by extraterrestrials is slim: when its composer, the late astronomer Frank Drake, gave the Arecibo message to his colleagues to interpret for fun, none of them succeeded.

That project, as well as the new experiment, illustrate just what a tall order true understanding between species is. “The beauty of A Sign in Space is to make us reflect on just how it is more frustratingly difficult and ultimately a much more profound sort of contact than Hollywood would ever portray,” says Douglas Vakoch, president of the organization METI (Messaging Extraterrestrial Intelligence) International, who wasn’t involved in the project. Though receiving an actual sign from aliens would be incredibly inspirational, what happens next might be less fun than movies suggest. “In the short term, it’s going to be incredibly boring and frustrating,” Vakoch says.

Message Extraction

From the first announcement, the project drew in an army of nerds and puzzle wonks. They flocked to Discord to exchange ideas, united by the belief that the message was ripe for solving.

One of the project’s more than 4,700 subscribers on Discord is Gonzalo José Carracedo Carballal, a 34-year-old Ph.D. student in astrophysics at the Complutense University of Madrid. A radio astronomy devotee, he fills his spare time working on radio wave projects in a room littered with instruments and parts. A satellite dish peeks from his balcony. Tattooed on his right triceps is an excerpt from the etchings on the Pioneer 10 and 11 probes’ plaque—another 1970s attempt by Earth scientists to introduce our species to any space aliens that might encounter the craft.

Carracedo Carballal was part of the first group of people to extract the raw message from the ExoMars orbiter’s broadcast. The communiqué was a 4.8-gigabyte string of numbers describing the waveform of the telemetry data, interwoven with the alien message. Unlike a real extraterrestrial note, which would arrive unannounced, this signal came in at a precisely scheduled time. Comparing the arrival timing with previous transmissions the telescopes received, the amateur code breakers identified a telltale data packet in the radio signal that was more active and sizable than usual. A week’s effort of filtering the data segment, which Carracedo Carballal likens to peeling layers off an onion, eventually led to an 8.2-kilobyte bitmap image of five speckled clusters set against a blank background.

Soon after Carracedo Carballal and his colleagues found the raw message, speculations on its meaning erupted. Perhaps the message was hinting at the aliens’ appearance, morse code, cellular automata or the genetic secrets of E.T. One user enlisted ChatGPT to reverse engineer a first-contact-appropriate message as a starting point. Several users suggested that the image was a star map broadcasting the civilization’s location. Others proposed that the dots represented constellations of a much punier scale: molecules, perhaps the biosignatures of the foreign home world.

The raw message looked too random to be comprehensible. Decoding was necessary to wrangle it into a more intelligible form. But where to start was the infernal question; every attempt would be a stab in the dark. “You start to see patterns,” Carracedo Carballal says of the process. “You have to stop and think whether something is actually there, or you’re just projecting.”

The Hard Part

Whenever Ivi Hasanaj, a 32-year-old software engineer based in Germany, starts to work on decoding A Sign in Space’s message for the day, he opens up the raw image on his computer and stares. He stares and stares some more until an idea occurs to him, and he writes code to manipulate the image.

Hasanaj doesn’t think aliens—or A Sign in Space’s organizers—are the sadistic sort who would make message recipients bang their head for nothing more than private amusement. Messages are meant to be understood. Although he hadn’t thought much about the problem of extraterrestrial communication before this project, Hasanaj has solved many puzzles on the gamified coding platform Codewars, and this experience comes in handy. For one, he recognizes the difference between decryption and decoding.

Decryption is the process of making sense of a concealed message for which only the intended recipient has a key, or a translation hack, to understand it. This kind of code breaking is much more difficult than decoding: the biggest hurdle is guessing the missing key.

On the other hand, a message with the key already embedded inside lends itself to decoding. When decoding, the user shouldn’t introduce new information into the message. Any operation on the raw file, such as a rotation or an overlay, should come from instructions that the reader has managed to extract from the message. Otherwise it would be like arbitrarily rearranging the letters of a word to arrive at a new anagram.

Hasanaj isn’t sure of the true content of A Sign in Space’s message, but his own best guess is a numerical system that counts from one to five. He uncovered this from observing a recurring pattern among the brightest pixels in the image.

But he hasn’t been able to account for the remaining flecks, which constitute the majority of the signal. Perhaps other kinds of information beyond math lurk in the message. He thinks no part of the already slim communication is redundant: aliens would probably make every pixel count. Whether or not he’s on the right track, he says he’ll know the correct answer when he sees it.

The community is still trying to decode the message—pursuing 30-some ideas for how to do so—before even attempting to interpret its full meaning. For this process, participants can take a less technical, and more cultural, approach to making sense of the message, as they might do for an abstract painting. For now, the signal is still too random to be interpretable. Watching their efforts unfold, de Paulis thinks these scattershot efforts may be distracting users from exploring each idea to the full. “They can't focus on one particular decision,” she observes. “I think that's the main problem.” If the public remains stuck on the decoding process, she says her team will likely organize an online hackathon later in August.

A Global Quest

Humanity’s best shot at understanding an extraterrestrial message is to throw a consortium of diverse expertise at it, Vakoch says. A Sign in Space is a shining example of what that may look like. So far the project’s eclectic group of volunteers have made impressive headway.

But in the event of a real extraterrestrial signal reaching Earth, the public isn’t likely to be invited to help with the decoding process. In 1989 the International Academy of Astronautics established a postdetection protocol that largely emphasizes secrecy. The guidelines have had little updating since. “An international committee of scientists and other experts should be established to serve as a focal point for continuing analysis... and also to provide advice on the release of information to the public,” the protocol decrees. “Parties to this declaration should not make any public announcement of this information” until the signal’s extraterrestrial origin is verified.

“The world has changed a lot since the 1980s,” says Franck Marchis, a senior planetary astronomer at the SETI Institute and an outreach and education coordinator for A Sign in Space. For one, there are many more radio aficionados like Carracedo Carballal who have rigged their own telescopes and trained them toward the skies. There’s also social media, which spreads news like wildfire. “The public will know no matter what,” Marchis says.

A Sign in Space is a dress rehearsal for scientific organizations to iron out the technical challenges of message sharing and telescope mobilization to confirm signal detection. More idealistically, it’s an experiment for sharing an extraterrestrial signal with members of the public and getting them involved. In that sense, A Sign in Space is the ultimate citizen science project, one on a planetary scale. De Paulis calls the participants on Discord her “co-creators.”

Marchis says he would love to make extraterrestrial communication and translation a more democratic affair. “I’d make the data available right away to the entire community of the world,” Marchis says, rather than having it “on the internal network of some random scientists.” That’s what drew him to A Sign in Space in the first place. “I’m hoping that this is going to be the way we’re going to move forward in the future,” he says.

Many members of the public would be more than happy to get involved in the real deal, but they aren't holding their breath. “So many cool theories [on] this server,” Hasanaj mused on Discord. The SETI Institute “should ask us to build the next message.”

Science Meets Art

In construing the meaning of an extraterrestrial dispatch, those who give it a go often try to anticipate what the message might be trying to say. The go-to answer is often science and math, given that these concepts hold up anywhere in the universe. The movie Contact posits that space aliens will hail us with numbers, throwing us a sequence of primes that look unnatural enough to make humans sit up and take notice.

But science and math won’t tell the recipients anything about the senders themselves. “If all I find is that the extraterrestrials know quadratic equations, I’m going to be very disappointed,” Vakoch says.

It’s one thing to flag a different species’ attention but another to converse meaningfully across the vast reaches of space. “I think an alien would send information that gives us an idea of who they are and the level of complexity that they have reached,” Marchis says—something that may even give recipients a glimpse of the alien society and its evolution.

This is where art comes in. Art is a creator’s self-expression and a cross-cultural conversation with its beholder. Perhaps the true meaning of an alien’s message is the composer’s original intent plus what the recipients make of it. Parsing such a message requires not only technical skill but also an artistic, philosophical flex. Thus, communicating with aliens is both a science and an art.

A Sign in Space recognizes the near futility of extraterrestrial communication and turns it into an endeavor that’s much more open-ended. “If we ever receive a message from an extraterrestrial civilization, I can imagine that there will never be an agreement over the cultural interpretation,” de Paulis says. “I think there would necessarily be some miscommunication.”

Understandably, the communication barrier can occasionally lead to griping. “It feels like interpreting clouds,” wrote one user on Discord. “Am I going crazy?” Humans sometimes forget that everyday communication with one another is also a miracle in itself. In response to a string of posts in French, one user, who failed to recognize the irony, replied, “Please speak English.” Moderators jumped in to say that all languages were welcome, which was followed by the French nonspeaker’s swift apology.

Editor’s Note (8/7/23): This article was edited after posting to correct the description of how Giacomo Miceli was recruited to A Sign in Space and the size of the communiqué’s string of numbers.