Back in March 1972, NASA launched Pioneer 10, the first space probe to complete a mission to the planet Jupiter and the first spacecraft to achieve escape velocity from our solar system. Carried on the space probe’s antenna support struts, in a position that would shield it from erosion by stellar dust, was a message to the universe; the Pioneer Plaque, carrying information about the human race and where we can be found, should advanced intelligent alien life ever detect and recover Pioneer 10.
I was born the same year that Pioneer 10 launched out on its interstellar mission, and last year I started looking into whether copies of the plaque are available. I discovered that the original plaque was manufactured by a small precision engraving company based in San Carlos, California. A bit more research and I found out that the company is still operating to this day and they still hold the original blueprint for the Pioneer Plaque! I got in touch with them and some guy called Poncino got back in touch to tell me the plaque is made of 7″x10″ brass plate, engraved and mounted onto a 9″x12″ solid walnut board. The original is gold-anodized aluminium, so by using a brass plate for the replicas, the plaque is the same colour as the original.
So, as my birthday was coming up, I figured a replica Pioneer Plaque would make an amazing gift. My girlfriend got on the case and after a month-long shipping period between California and England, the package arrived and I’m now the proud owner of one of these great plaques.
This plaque is manufactured to a high quality. The brass plate is well finished on the edges and the etching is accurate, with no spillover or anomalies. It is glued down onto the solid walnut board and there are hanging slots in the back of the plaque, along with some description, as follows:
The Pioneer 10 spacecraft, destined to be the first man-made object to escape our solar system, carries this plaque. It is designed to show scientifically educated inhabitants of some other star system – who might intercept it millions of years from now – when Pioneer was launched, from where, and by what kind of beings. The design is engraved into a gold-anodized plate, 152 millimeters by 229 millimeters (6 by 9 inches), attached to the spacecraft’s antenna support struts in a position to help shield it from erosion by interstellar dust. The radiating lines at left represent the positions of 14 pulsars – cosmic sources of radio energy – arranged to indicate our Sun as the home star of the launching civilization. The “1-” symbols at the ends of the lines are binary numbers that represent the frequencies of these pulsars at the time of launch of Pioneer F relative to that of the hydrogen atom shown at the upper left with a “1” unity symbol. The hydrogen atom is thus used as a “universal clock”, and the regular decrease in the frequencies of the pulsars will enable another civilization to determine the time that was elapsed since Pioneer F was launched. The hydrogen atom is also used as a “universal yardstick” for sizing the human figures and outline of the spacecraft shown on the right. The hydrogen wavelength – about eight inches – multiplied by the binary number representing “8” shown next to the woman gives her height – 64 inches. The figures represent the type of creature that created Pioneer. The man’s hand is raised in a gesture of good will. Across the bottom are the planets, ranging outward from the Sun, with the spacecraft’s trajectory arcing away from Earth, passing Mars, and swinging by Jupiter.
The ‘Pioneer F’ mentioned in the text was the original designation for Pioneer 10.
How Did It All Begin?
The idea of the Pioneer space probe carrying a message from humankind was conceived by an English lecturer and journalist, Eric Burgess, who was a reporter on the Pioneer program of space mission since they began in 1957. He approached the science communicator and author, Carl Sagan, who had presented talks on communication with extraterrestrial intelligences. NASA agreed to sending a message out on Pioneer 10, and with three weeks to the launch, Sagan and American astrophysicist Frank Drake started putting together the pieces of information to go onto the plaque, with Sagan’s wife., Linda – an artist and writer – designing the final composition.
Digging Into The Detail
There are five symbol sets on the Pioneer Plaque, each one designed to allow advanced extraterrestrial life to locate and identify our species and the planet that we live on. Each of the symbol sets is quite heavily science-based. Although I studied organic chemistry at Hull University for three years back in the mid-90s, it still took me some time to get my head around it all. The passage above explains most of it adequately, but the way that hydrogen measurements are used to explain the rest of the plaque needs a bit more explanation.
Top Left: The Hyperfine Transition of Neutral Nitrogen
This is the one part of the plaque that pulls everything else together, providing time and distance measurements and creating meaning to the map.
The diagram shows two atoms of hydrogen, the most abundant visible element in the universe and one that any intelligent extraterrestrial civilization with an astronomical and physics-based understanding will be able to recognise.
Hyperfine transitions are just an explanation of how neutrons, protons and electrons interact with each other in the ground state. These subatomic particles spin at different speeds, the electron and neutron are half the spin speed of the proton, so half the time they are spin-parallel and the other half spin-antiparallel. The plaque depicts this as shown in the close-up photo below.
As the electron and neutron flip, they interfere with radiation patterns and ‘chirp’ at a particular wavelength and speed. The wavelength is 21cm and a frequency (speed) of 1420MHz, which is 1,420,000,000 cycles per second.
There is perhaps an average of one hydrogen atom per cubic centimeter of interstellar space, so these individual atoms chirping away at 1420 MHz make a powerful chorus, which is readily detected by radio telescopes on Earth. A sentient extraterrestrial species should have access to the same fundamental understanding.
A Very Human Blunder
After Pioneer 10 had launched, the scientific robustness of the plaque’s imagery came into question. Most of the information can be decoded using the hydrogen lengths and time, but a basic identifier at the heart of human evolution could be a complete puzzle to extraterrestrial life. The problem? An arrow…
An arrow depicts the path of Pioneer 10 from Earth, past Mars and sling-shotting around Jupiter to propel it into the outer reaches of our solar system and beyond our heliosphere, the immense magnetic bubble that contains our solar system, solar wind, and the entire solar magnetic field. The arrow is one of the easiest parts of the symbol sets for a human to decipher – our species grew up hunting other animals with arrows that we launched from our hands. It’s a ubiquitous symbol of direction. But would an extraterrestrial being have the same cultural toolset to be able to decipher the meaning?
With Pioneer pressing on through our solar system, nothing could be done. The revelation came too late.
An Exercise In Futility Or The Most Incredible Meshing Of Art And Science?
The plaque itself is symbolic; the odds of an alien species ever intercepting the probe is almost non-existent. Completely negligible. However, it may be the most enduring legacy of humanity and will undoubtedly outlive our species and even our planet. Even if extraterrestrial life exists – which is highly likely – and it can travel from star system to start system, what’s the likelihood of it coming into contact with a piece of space junk about the size of a small shed? But when you consider our other legacies: the pyramids, the Great Wall of China, Stonehenge, the Panama canal, or eve the Internet and computer data, that may last a few hundreds of thousands of years at the absolute most, it is both incredible that we could do so much with such primitive technology and understanding, and humbling that the best we can do with our most advanced technology is send a tiny message that will be utterly lost in the vastness of space. Could this one act be the most optimistic, joyous and yet pitifully pointless performance our insignificant planet will ever produce? It is truly beautiful.