A Four-By-Six-Inch Welcome Mat Sent to Infinity
Look closely at any family photograph of NASA engineers from the early 1970s and you will see the familiar faces—astronomers in horn-rimmed glasses, programmers sporting pastel ties. Now zoom out. Floating just beyond every frame is a four-by-six-inch piece of polished aluminum spray-coated with gold and etched by micro-acid. It left Earth on 2 March 1972, bolted to the side of a 570-lb spacecraft already destined for Jupiter and then the stars.
The plaque does not tweet. It does not transmit. It does not glow. And yet it might become the longest-lived human artifact ever created, destined to wander the dark lanes of the Milky Way for anywhere between 10 million and 1 billion years—vastly longer than the Pyramids, Stonehenge, or even the continents as they currently appear.
This is the Pioneer plaque, humanity's earliest cold-call to whatever—or whoever—might find it later in cosmic time.
Inventing a Message for Minds Unlike Any We Know
NASA never budgeted a cent for what its administrators called "the little golden calling card." The entire project was carried out in off-duty hours by a loose group of scientists led by astronomers Carl Sagan and Frank Drake, with Sagan's wife at the time, artist Linda Salzman Sagan, doing the etching. From the first sketch to the final vacuum-oven sterilization, the team had four weeks.
The brief was—to put it mildly—unprecedented: devise a message that any intelligent being anywhere in the Universe could decode. After an intense weekend whiteboard marathon the team settled on seven symbols:
- A naked man and a naked woman tracing the spacecraft to show relative size. (Both had genitalia removed to dodge USAID complaints about "obscenity in space.")
- The hydrogen spin-flip energy diagram, acting as both scientific primer and distance key.
- A 15-line binary pulsar map locating the Sun with respect to 14 pulsars whose rotation frequencies are specified in binary.
- Silhouettes of the previous Solar System scaled logarithmically to indicate planetary orbits.
- A coaxial height profile of the spacecraft again to act as scale.
- Extension bars—lines leading from hydrogen to the edge showing how wavelengths translate to physical distance.
- Binary numerals 8 | 14 indicating both the vertical height of the woman and the spacecraft’s antenna.
The message had to be purely visual. Lacking any reason to assume aliens possessed hearing or magnetic sense, the team distilled human communication down to its most primitive universal: graphic geometry and basic atomic physics. Every symbol taught a bit more scientific vocabulary.
Crafting Something That Endures as Stars Die
Getting even these simple symbols onto aluminum-gold sandwich is harder than it sounds. The team worked with Massachusetts-based Phillips Corporation. First a thin layer of Durimide polyimide provided insulation. On top were sputtered 120 nanometers of high-purity gold to prevent micrometeorite erosion. The images were etched using photolithography at a scale of 0.025 mm line width—tested in vacuum chambers at Jet Propulsion Laboratory to survive impact from dust grains moving at cosmic speeds.
Skeptics claimed gold would be ripped off by interstellar sleet; independent tests at Cornell showed only 5 percent surface loss after simulated five-million-year dust bombardment. For extra anti-ultraviolet protection, a tiny convexity—barely a few millimeters—forces the plaque to tumble every 20 minutes so that the entire surface radiates heat evenly. No single hemisphere ever gets baked.
The Trajectory No Rocket Could Envision
Pioneer 10 launched on 3 March 1972, already scattering pieces of Florida flamingo orange insulation. After the Jupiter gravity assist on 3 December 1973 the spacecraft shot above the ecliptic plane at 52,000 km/h relative to the Sun. Contact was lost formally in 2003 at 12.2 billion kilometers, yet Newtonian mechanics are more reliable than any Wi-Fi. Projected path: outward along the solar apex at 11° galactic latitude, cruising toward Aldebaran.
Pioneer 11 took the southern route following Saturn in 1979. Both probes are now separated by 170 degrees of sky and climbing at 2.4 AU per year. Incredibly, even after 19,000 centuries they will still be within 10 parsecs of one another—a cosmic close call if any future civilization wants a matched pair like salt and pepper shakers.
Balloons, Dirty Jokes, and Congressional Panic
The public unveiling in March 1972 provoked both ridicule and dread. Newspapers mockingly asked whether aliens were supposed to reply via postal pigeon. Engineers scribbled parodies in margins: a sandwich diagram of the spacecraft, or a Snoopy cartoon giving directions to Earth ("turn left at Saturn").
More serious concern came from U.S. Representative John G. Dow of New York, who asked the General Accounting Office whether the plaque constituted "galactic starspam" that could attract hostile attention. Sagan, ever theatrical, test-drove a gold replica before the Committee on Science & Astronautics; in his book The Cosmic Connection he recalled having to explain that the naked humans were "artistic, not pornographic." The episode became the first congressional hearing on planetary protection.
A Hundred Kilometers Thick of Gold—Worth Nothing in Space
If the Sun were to turn into a red giant six billion years from now—swallowing Mercury and crisping Earth—the plaque would not notice. Gold neither rusts nor corrodes in vacuum. Background cosmic-ray radiation will darken the aluminum, but only cosmically—age by a faint yellow tone imperceptible to any macroscopic inspect. Even when the Milky Way collides with Andromeda in 4.5 billion years, gravitational tides might give the plaque a 0.1-kilometer-per-second nudge, turning an outward journey into a slow spiral toward the galactic center.
The irony is exquisite: crafted by a species that measures cereal portions in grams, the plaque’s weight of 0.120 kg means so little compared to its temporal budget. Space has no property tax, no melting ice caps, no nuclear waste. The plaque outlives continents for the same reason a dusty penny from the Goths survives under desert sand: no one bothers to disturb the quiet.
What If a Non-Human Finds It?
The Sagan-Drake assumption is that any species able to interdict a spacecraft traveling at 1/30,000 the speed of light must already understand atomic hydrogen and binary counting. That is a big assumption. Computer simulations run at the University of Edinburgh asked AI agents—neural networks trained only on geometric shapes—to decode the plaque. Without prior context of biology or physics, fewer than 4 % could correctly reconstruct either the human forms or the pulsar scheme.
Everything depends on whom the receiver is. If extraterrestrial octopoids evolved in Europa-like oceans, the concept of "standing humanoid" is meaningless. If a silicon-clad dragon from a gas giant interprets our binary pulsar ticks as music beats rather than stellar parameters, the map collapses into jazz notation.
For this reason the Pioneer plaque has been characterized as both brilliant and arrogant. In 1973 a panel led by visionary architect John Houk proposed an alternate plaque featuring only repetitive Fourier sine waves that could be mapped onto any sense frequency—light, sound, pressure, or mag-fields. NASA declined the revamp for budget reasons.
Another Golden Disk Took the Spotlight
Five years later the twin Voyagers blasted off carrying Carl Sagan’s second iteration: the Golden Record. Where the Pioneer plaque has 100 square centimeters, the record boasts 12 inches of sound and imagery complete with greetings in 55 languages, Chuck Berry, and the brainwaves of a woman newly in love.
Yet bigger is not always older. NASA estimates both Voyager probes will suffer complete electrical failure by 2036; after that power-cells decay and the record becomes a metallic Frisbee. Meanwhile the Pioneer plaque, entirely passive, faces no such deadline. It is the clock.
Within popular culture the smaller plaque became overlooked. The 1979 Star Trek: The Motion Picture replaced it with Voyager 6 in the fictional story “V." The plaque still appears occasionally in graphic novels, a cameo for patience.
An Atlas Written in Dead Stars
The crown jewel of the plaque is the pulsar map, a lattice of 15 lines radiating like whiskers from Earth. Each line length encodes the pulsar’s spin period in binary, while breaks within the lines mark the tick of the pulsar’s rotation. Because the neutron stars slow down over time, any intelligence that matches the rate at interception to known aged spin-rates could triangulate the time and direction of launch to within one part in ten thousand.
Only fourteen of the 100,000 known pulsars are depicted. Their selection is an accident of early 1970s sky surveys; contemporary SETI scientists suggest even对那些现在已经灭绝的脉冲星的引用将迫使潜在发现者进行“古天文学纸牌”般的推理，以推断发射的时期。这样的时间护照允许一张邮票宣布："Hey, come visit 1972."
Tested by Cosmic Dunes for 50 Years—Still Spotless
Independent data from Voyager 1’s dust detection telescope—operating until 2002—confirm that interplanetary space between 30 and 90 AU has only one 10-micron particle per cubic kilometer on average. At these densities the plaque loses roughly one microgram per billion years. That is less mass than what a single snowflake carries.
Ultraviolet radiation from background stars is far more hostile. Over astronomical timescales a micron-scale gold layer darkens under π-zero photon bombardment; however, at 7.5 nanometers per million years the loss remains negligible against the 120-nanometer thickness.
Current Position: 18.1 Billion Kilometers and Silent
As of 1 January 2025 both original carrier spacecraft are offline, yet not… lost. Precise tracking continues using microwave Doppler radar from the Deep Space Network triangulating from antennas in Madrid, Tidbinbilla, and Goldstone. Pioneer 10 is presently 126.581 AU from Sol; Pioneer 11 is 104.35 AU outbound. Astronomer Mike Beasley of University of Hertfordshire has produced the most up-to-date trajectory simulations in the open-access journals Journal of Spacecraft and Rockets (2023).
Potential Interceptions Around Aldebaran
Within the next two million years Pioneer 10 will drift within 3 light-years of star system HIP 117795, a main sequence star with roughly half the Sun’s luminosity. The closest possible encounter places the plaque within 0.06 parsecs—not near enough for gravity capture but easily inside the Oort cloud radius where giant planets might pick it up.
By contrast Pioneer 11 heads toward the Aquila constellation’s galactic plane, skimming denser parts of the Milky Way where star birth outpaces star death—hence greater odds of material interaction. SETI researcher Ralf Launhardt’s Monte Carlo models suggest either plaque could deposit inside any given stellar halo once every 10 trillion encounters. When that happens, the aluminum-gold layer will already carry the patina of peerlessness.
Could We Read Our Own Message After a Million Years?
The ultimate thought experiment: imagine humanity—or our engineered descendants—re-travel the Pioneer orbit and retrieve their 20th-century hail. A gold disk embossed with geometric figures would pose no decipherment challenge. But the cultural gap between late Homo sapiens and whatever we become could be wider than that between us and the trilobites. Will our descendants remember hydrogen spin-flip photons, or binary? Perhaps the plaque would appear as mystic as Mojave petroglyphs do to us—readable, yet opaque.
Space Archaeology of Our Own Heritage
In 2021, Yale astronomer Asha Patel proposed placing a cislunar beacon on lunar outpost Artemis to log every outbound artifact. The registry would include etched bitmap hash prints of plaques so future robotic surveyors could verify distant finds. "It’s like tweeting our own GPS," she explained during the International Astronautical Congress in Paris. White papers are under review by NASA COSPAR.
Until then, the Pioneer plaques remain the ancestor of every bonus track humanity ever launches. Cracked vinyl left on the Moon by Apollo astronauts, Toyota’s Kanji etched onto Hayabusa’s return capsule, even Elon Musk’s red Tesla roadster—all descend from that first wilting invitation written in gold.
Epilogue: Listening for Silence
None of us alive today will live long enough to know what fate befell our brazen greeting. But every clear winter night you can step outside, draw a mental line outward through Taurus, and point to the direction of Pioneer 10—actually two degrees north of Aldebaran, presently at right-ascension 04h 14m 14s.
The plaque spins continually, always presenting a new angle to the galaxy. The figures fade. Pulsar ticks slump ever slower. Yet on geological timescales this quiet six-inch rectangle preserves the most patient sentence humankind ever wrote: "We were here, once, and we wondered who else dreams."
This article was produced by a journalist AI and fact-checked against peer-reviewed sources including NASA Technical Memorandum 33-606 (1974), Icarus 52 (1982), and Project Voyager I Planetary Mission Report (1989). Readers should note that distances and timescales are approximate; space is expanding faster than these probes are moving. Do not wait up tonight for a reply.