I have a tattoo on my leg that is often mistaken for a firework or a sparkler. It’s a long stem leading up from just behind my ankle bone to two-thirds of the way up my calf. Fourteen rays shoot off from the central point of the stem’s top—lines of different lengths, some interrupted into dashes, some paralleled by a second line for part of their length. The only people who know what it means are those who are already familiar with the symbol, at least when they encounter it on my leg. But it was originally designed for viewers who would know even less what to make of it, if they even had the senses to process it.

The symbol is called the pulsar map, a representation of our solar system’s place in the galaxy, cross-referenced against the galactic center and 14 pulsars, each represented by one ray of the seeming starburst of the design. A pulsar is the the remnant of a massive supernova, now a neutron star, rotating at an incredibly high speed. It shoots a powerful beam of radiation that, thanks to its spin, pulses like a metronome, or a lighthouse signal, each to its own rhythm. Here, their distance from Earth is shown in the length of their ray, the frequency of their pulse is shown by a dashed line, and their orientation in the galactic plane — the galaxy being disc-shaped — is indicated by a little tick mark somewhere along the ray.

The idea is that if an intelligent alien comes across this map, floating somewhere out in space, they could figure all of that out.

The pulsar map is best known as a component of the cover of the Voyager Golden Record, the 12-inch discs each attached to the pair of Voyager probes flung to the far reaches of the solar system in the 1970s. The probes were designed to visit Jupiter and Saturn, but NASA knew they’d have enough momentum to keep trucking on through — and out of — the solar system. And so, in a gesture of great romanticism, they commissioned Carl Sagan to adorn the probes with some sort of return address and, more than that, a message to whoever might find them.

Photo by NASA/Hulton Archive/Getty Images

This wasn’t the first project of its kind, but it was the most ambitious. Previously, Sagan and Frank Drake had designed plaques for the Pioneer probes — they also feature the pulsar map; a line drawing of a man and woman, the man’s hand raised in a wave; and a schematic diagram of the solar system, with a little Pioneer drawn on its way out. But the Voyager record holds much more. Once you decode the cover schematics, you have not just an origin for the strange spacecraft you’ve found, but also instructions for playing the record.

Many love songs have been written to the Golden Record — there’s the Radiolab episode with Sagan’s widow, Ann Druyan, telling the story of how the couple fell in love during its creation, and Anthony Michael Morena’s lyric book, The Voyager Record, which is beautiful and rigorously researched. I’m obviously of this romanticizing persuasion—I do have a piece of the record’s cover art tattooed onto my leg. But do we love the Golden Record because we hope aliens will one day find it? Or is it the pure hopefulness of the gesture that we love? That NASA once took time and money to create this idealistic gift? And is it idealistic for the scant hope that someone will find the record, let alone understand how to play it? Or, though I’m not the first person to ask this: Is the message of the Golden Record meant just for us?

There are two ways to take that last question. The romantic way: The process of devising the record, of deciding what would go on it, and how we, as humanity, wanted to represent ourselves, was the most meaningful act. In that view, the Golden Record becomes an aspirational self-identification, a declaration to ourselves: We are a global people; we are hundreds of languages and a child’s laughter; we are music and whale song, heartbeats and the brainwaves of a woman falling in love.

But are we the likeliest people to find the Golden Record? The Voyager probes have by now passed the murkily defined boundary of the solar system. However you calculate it, they’re surely now in interstellar space. They’re the only objects from Earth out there. But maybe not forever. The only technological civilization we’re sure exists is our own, so the likeliest interstellar travelers to come across the Voyager probes could very well be far-future humans. Even if the probe doesn’t metastasize its own intelligence like V’ger in Star Trek: The Motion Picture, it could, given several thousand years, become alien to us — because we could become alien to ourselves.

Ten thousand years ago, humans were physiologically just as we are now, but they were culturally incomprehensible. They left us cave paintings that we recognize as made by human hands, but that’s as far as our understanding goes. Were they messages, art, religious ritual, or bored doodles? Any meaning they may have held is utterly lost.

Ten thousand years isn’t an arbitrary measure of time here — I bring it up because it’s exactly the gulf across which we are trying to figure out communication, for the warnings to be designed for the future nuclear waste disposal site at Yucca Mountain in New Mexico, the contents of which will be dangerously radioactive for a hundred centuries. How do we make a warning that will stay intelligible for as long?

A common way to emphasize the scope challenge is to take a walk through the history of the English language: Middle English, spoken 600 years ago, is barely comprehensible to a contemporary English speaker; Old English, from a thousand years ago, isn’t comprehensible at all. It’s a matter of entropy, in a way, information subject as anything else is to the Second Law of Thermodynamics — order decaying into randomness, meaning abrading over time. And that’s with a relatively contiguous culture. Imagine a disaster, or a social break: Humanity survives, perhaps fully rebuilds, and encounters a mystery in the desert. You need these future humans to not only understand the warning, but also believe it — after all, all the promised curses in the world didn’t stop 19th-century archaeologists from broaching the sealed doors of the pharaohs’ graves.

Seventeen years ago, the Department of Energy convened a commission of anthropologists, linguists, semioticians, and other experts to figure out how to make a universal message. Every option they proposed feels like a conceptual art project, but maybe that’s not so surprising. When you discount any carrier of meaning that’s tied to our current culture — a sign that says “keep out” or the broken circle sign for radioactivity — what you’re left with is the visceral, nonverbal evocation of feelings that are, we hope, universal for humanity. In this case, the panel hoped for the evocation of fear, awe, or disgust. “What is here is dangerous and repulsive to us. This message is a warning about danger,” as well as “This place is not a place of honor…no highly esteemed deed is commemorated here…nothing valued is here.”

The panelists ended up with a project in many mediums, hoping to cover their bases with redundancy: Rosetta stone–style plaques in half a dozen contemporary languages, imposing granite columns surrounding the site, warnings in words and image and mood. Three rooms will hold identical information about the project — two hidden, buried and walled with granite, and one at the center of the array of columns. To let in natural light, it will have no roof, I think because we have no idea if, in 10,000 years, humans will still have electric power.

Discarded ideas brainstormed by the commission include a field of massive stone spikes, set at random angles like thorns, to convey terror and inhospitability, and a generational game of telephone, breaking the 10,000 years into 300 generations and tasking every third generation with adapting their great-grandparents’ message into new, contemporary language, so that it might not be irredeemably alien to their own great-grandchildren.

Also dismissed: seeding a 10,000-year folklore, a mythic “false trail” that would use superstition rather than scientific knowledge to urge people to shun the site. It would be overseen by an “atomic priesthood” in the know, the keepers of the radioactive truth. (The proven ineffectiveness of warnings at the pharaohs’ graves made this one even easier to dismiss.)

Words, maps, scientific notation, landscaping, abstract sculpture. In their report, “Communication Measures to Bridge Ten Millennia,” the panel wrote, “Every form of physical energy propagation can be used as a channel for conveying messages.…It is important, furthermore, to appreciate that human senses register only a small portion of ambient stimuli.” Even on Earth, there are organisms that have different senses than ours — whales with their sonar, birds that follow magnetic fields, plants that process touch to wind their tendrils. Dogs hear sounds we don’t hear; bees see light that for us is invisible. Not every animal sees. Even some humans communicate not with sound, but with gestures.

I’m not sure even the creators of the Golden Record themselves thought that its message would be decipherable. Look at its simpler cousin, the Pioneer plaque—you’re a human, this was made by other humans, but what parts of it do you understand?