Bolted to the antenna support strut of Pioneer 10, hurtling outward from the Sun at roughly 27,000 miles per hour, there is a six-by-nine-inch slab of gold-anodized aluminum engraved with the silhouettes of a naked man and woman, a map of fourteen pulsars, and a diagram of the solar system. The whole thing was designed in about three weeks.
Carl Sagan got the idea late. The launch was already scheduled. NASA, when asked, said yes.
What followed is one of the strangest commissions in the history of spaceflight: a message to any intelligence that might one day intercept the first object humans had ever flung past Jupiter, drafted in less time than most agencies take to approve a press release.
A three-week deadline to speak for the species
The plaque concept was suggested to Sagan only a few months before Pioneer 10’s March 1972 launch. He brought it to NASA. NASA approved it, and gave him three weeks to prepare a message. Sagan then worked with Cornell astronomer Frank Drake, of Drake Equation fame, and his wife at the time, the artist and writer Linda Salzman Sagan, who drew the human figures. The whole design was assembled in roughly three weeks.
Three weeks to decide what humanity looks like to a stranger. Three weeks to choose a coordinate system, a unit of measurement, a posture, a gesture, a level of nudity.
The constraints were brutal. Whatever they engraved had to be intelligible to a mind that shared none of our biology, none of our language, and none of our cultural references. It had to survive billions of years in interstellar space. And it had to fit on a plate the size of a car license plate.
The physics they chose as a common language
The upper left corner of the plaque shows two circles connected by a line: the hyperfine transition of neutral hydrogen. When a hydrogen atom flips the spin state of its electron, it emits radiation with a wavelength of 21 centimeters and a period of 0.7 nanoseconds. Hydrogen is the most abundant element in the universe. Any civilization capable of building radio telescopes will have measured this transition.
That single diagram sets the ruler. Everything else on the plaque, every distance, every duration, is expressed as a multiple of that wavelength or that period, written in binary tick marks.
The woman on the plaque is drawn eight hydrogen-wavelengths tall. Eight times 21 centimeters is 168 centimeters, about five feet five inches.
The pulsar map, and why it doubles as a timestamp
The starburst pattern in the middle of the plaque is the most technically dense piece of information on the entire object. Fourteen lines radiate from a single point, the Sun, each pointing to a pulsar. The length of each line encodes the distance. The tick marks along each line encode the pulsar’s rotation period, again in binary, again in units of the hydrogen transition.
Pulsars slow down over time at known rates. A sufficiently advanced civilization could read the periods, identify which pulsars they correspond to, and calculate roughly when the plaque was made. The map is both an address and a date stamp, accurate to within a few thousand years over a span of tens of millions.
Below the starburst sits the simplest panel: a row of circles representing the planets of our solar system, with a small arrow showing the Pioneer probe leaving Earth, the third one out. Pluto is included. The diagram was engraved before the term “dwarf planet” existed.
The figures, and the controversy they walked into
Linda Salzman Sagan drew the man and woman with deliberately ambiguous ethnic features. Both stand naked. The man’s right hand is raised, palm out, in a gesture intended as a greeting, though there is no guarantee an extraterrestrial would parse it that way. The plaque also conveys, almost as a side effect, that humans have opposable thumbs and a particular range of arm motion.
The figures generated immediate cultural friction once the plaque was made public. Newspapers in 1972 received complaints about nudity on a NASA spacecraft. Other readers objected that the man was depicted with the active, communicative gesture while the woman stood passive. There was also the question of what the figures showed and what they didn’t. The final engraving renders the man fully but omits the vertical line on the woman’s body that would have indicated the pudendal cleft. Per Carl Sagan’s own later account, the omission was deliberate and was made by the designers, not by NASA. Sagan said the decision rested on two reasons: Greek sculptures of women, which the figures were partly modelled on, did not include that line, and he suspected that a more explicit drawing would not have survived NASA’s approval process given the three-week timeline. The plaques were manufactured at Precision Engravers in San Carlos, California, and that compromise is the version that flew.
The asymmetry is real. The reasoning behind it was Sagan’s own.
How the plaque was actually made
The engraving was done by hand. Only three originals were produced in 1972 and 1973: two for the spacecraft and one kept by NASA. The engraver, Ponciano Barbosa, was still working at Precision Engravers more than four decades later, when designer Duane King tracked him down to produce authorized replicas for the mission’s 45th anniversary.
As Smithsonian Magazine reported in 2017, the replica project found a buyer base of space enthusiasts willing to pay $399 for a hand-engraved copy, and the Kickstarter cleared its $70,000 production goal. The plaque, in other words, has become a design object on Earth even as the originals slip further into the dark.
Where the plaques are now
NASA lost contact with Pioneer 11 in 1995. Pioneer 10’s last faint signal reached Earth in January 2003, when the probe was about 7.6 billion miles away and its plutonium power source had finally decayed below the threshold needed to run the transmitter. Both probes are still out there, still carrying their plaques, still moving.
Pioneer 10 is heading roughly in the direction of Aldebaran, the red eye of Taurus, about 65 light-years away. At its current speed, it will take more than two million years to get there. Pioneer 11 is aimed toward the constellation Aquila and faces a similar journey, with a near pass of the star Lambda Aquilae projected at around four million years from now.
The probability that either plaque will ever be found by another intelligence is essentially zero. The galaxy is mostly empty. The probes are small. The plaques face inward, bolted against the antenna struts to shield them from interstellar dust erosion.
What the Voyager records added five years later
By the time Voyager 1 and Voyager 2 launched in 1977, Sagan had been given more time and a much larger canvas. The gold-plated phonograph records bolted to those spacecraft carry 115 encoded images, greetings in 55 languages, natural sounds from Earth, and roughly 90 minutes of music ranging from Beethoven and Stravinsky to Chuck Berry’s Johnny B. Goode. The cover of each record repeats the hydrogen diagram and the pulsar map from the Pioneer plaque, a deliberate continuity. As NASA’s Golden Record contents page describes, the records include instructions for how to play them, including the playback speed of 16⅔ revolutions per minute, with a calibration circle so the recipient can confirm the decoded image has the right aspect ratio before moving on to the rest.
Both Voyagers are still transmitting, more than four decades on. The Pioneers are silent. The plaques are mute by design.
The unsolved mystery the Pioneers left behind
For decades, tracking data from Pioneer 10 and 11 showed a tiny, unexplained acceleration pulling the probes back toward the Sun, a deviation from predicted trajectories of about 8.74 x 10⁻¹⁰ meters per second squared. As summarised in the Pioneer anomaly literature, the effect puzzled physicists for nearly thirty years and prompted serious proposals about new physics before a 2012 reanalysis attributed the entire signal to anisotropic thermal radiation emitted by the probes’ own onboard systems. The anomaly was, in the end, the spacecraft warming themselves unevenly.
The plaques know nothing of this. They are gold, etched, silent. They were never meant to report back.
What a three-week message says about the people who made it
Sagan’s instinct was that something should ride along, even if no one ever read it. The decision to include the plaque was, at the time, a relatively cheap addition: a few hundred dollars of materials, a few weeks of design, a small mass penalty for a spacecraft built around a plutonium battery and a high-gain antenna. The scientific case was thin. The symbolic case was everything.
This kind of optional, almost private gesture surfaces repeatedly in spaceflight history. Inverse has tracked the ongoing ethical debate over deliberately transmitting messages to other stars, a practice called METI, and the arguments over Pioneer-style passive plaques look almost quaint by comparison. The Pioneer plaque sits in the same category: a personal mark inscribed on a public mission, slipped aboard before anyone could think too hard about whether it should be there.
The drawing is still moving
Right now, as you read this, the woman on the Pioneer 10 plaque is roughly 13 billion miles from Earth, traveling outward at about 27,000 miles per hour relative to the Sun. She has not aged. The gold has not tarnished, because there is almost nothing out there to tarnish it. The hydrogen diagram in the upper left still encodes the same wavelength it did in March 1972, when Richard Nixon was president and the first commercial pocket calculators were going on sale.
If anything ever does find the plaque, it will likely be long after the Sun has expanded into a red giant and swallowed the Earth. The drawing of the two humans, waving or not waving, will outlast every person who has ever lived, every building ever built, and probably the planet they were drawn on.
Three weeks of work. A few hundred dollars of gold. A handful of binary tick marks. And a single line, deliberately left off the body of a woman who will keep moving outward for the next two million years.
