Jake RosenthalJan 20, 2016

The Pioneer Plaque: Science as a Universal Language

In 1972, an attempt to contact extraterrestrial life was cast into space with the launch of the Pioneer 10 spacecraft. This space vehicle was designed to explore the environment of Jupiter, along with asteroids, solar winds, and cosmic rays. Among a succession of firsts achieved by the spacecraft, Pioneer 10 would attain enough velocity to escape the solar system. This tacked on yet another first: the possibility of the interception of a human machine by an extraterrestrial civilization, providing us the opportunity to make contact with life from another world.

The suggestion of a message on Pioneer 10 was brought to Dr. Carl Sagan mere months before launch—a staggeringly brief period in the timescale of the design and test of spacecraft. Sagan passed along the idea to NASA, and to his surprise, the suggestion was embraced and approved by every level of the hierarchy. At that, Sagan joined Professor Frank Drake of Cornell University and, Sagan’s then-wife, artist Linda Salzman Sagan, to craft this extraterrestrial message. How would this great undertaking be fulfilled? What would we say? What in our roughly five-thousand-year recorded history needs to be said to tell the universe who we are? And how would we say it?

Humans speak nearly seven thousand languages, some with multiple dialects. The countless other species on Earth communicate with innumerably more, nearly all of which we have, thus far, failed to understand. By extrapolation, it is presumable that an alien language is different than any language we have developed. Human languages are products of human minds, and thereby, can be understood by human minds, by means of human senses—sight, sound, touch. How could we begin to imagine an extraterrestrial language if we cannot imagine with what senses the beings communicate? They may not have vocal chords with which they produce sounds or ears with which they capture them. So we must rely on universally-understood concepts, and devise a communication method neither specific to location nor species nor world. Perhaps, the only similarity between our species is the universe in which we both live. Thus, the language we are most likely to share is the study of the universe itself: science. The result of this conclusion was the Pioneer Plaque.

The illustrations on the Pioneer Plaque
The illustrations on the Pioneer Plaque

The Pioneer Plaque is a physical, symbolic message affixed to the exterior of the Pioneer 10 spacecraft. At the core of this message is a fundamental concept that establishes a standard of distance and time, which, thereafter, is employed by the other components of the plaque. The design team postulated that hydrogen, being the most abundant element in the cosmos, would be one of the first elements to be studied by a civilization. With this in mind, they inscribed two hydrogen atoms at the top left of the plaque, each in a different energy state. When atoms of hydrogen change from one energy state to another—a process called the hyperfine transition—electromagnetic radiation is released. It is this wave that harbors the standard of measure used throughout the illustrations on the plaque. The wavelength (approximately 21 centimeters) serves as a spatial measurement, and the period (approximately .7 nanoseconds) serves as a measurement of time. The final detail of this schematic is a small tick between the atoms of hydrogen, assigning these values of distance and time to the binary number 1.

The most prominent figures on the plaque are those of two adult humans: a man and woman. The man bends his arm and displays an open palm—an international greeting, but one that, admittedly, may be meaningless to an extraterrestrial civilization. The woman hangs her arms by her sides and stands with her weight shifted rearward as to dispel any misunderstandings regarding a fixed body and limb position; we are mobile and flexible. Beside the illustrations of the humans is the binary number 8, inscribed between two ticks, indicating the height the woman. The civilization could then conclude that the woman is 8 units tall, the unit being the wavelength (21 centimeters) described by the hyperfine transition key; thus, the woman is 8 times 21 centimeters, or about 5.5 feet tall.

At the heart of the plaque is an array of lines and dashes—a cosmic address on the interstellar letter. In the center is our home star; the radial spokes signify the relative distances and directions to pulsars—rapidly rotating neutron stars that emit electromagnetic radiation at regular intervals. Accompanying each line is the period of the respective pulsar—once again, in binary. Not only does this map communicate position, but time as well—an epoch in the lifetime of the universe during which the message was sent. The rate of electromagnetic bursts from pulsars changes over time; thus, the period of the pulsars denoted on the plaque serves as a timestamp. It is presumed that a civilization that has developed radio astronomy will have the capability to comprehend the nature of pulsars. Given the information presented in the pulsar map, it is feasible that such a civilization could date back the message and triangulate our position. As further confirmation of our locale, our solar system’s planets (nine at the time) are depicted in the bottom margin of the plaque with their respective distances to the sun in binary. Supposedly, in the history of the Milky Way, only one star has ever fit the characteristics displayed on the plaque.

Pioneer Plaque
Pioneer Plaque The Pioneer Plaque fixed to the Pioneer 10 spacecraft.Image: NASA

The last signal from the Pioneer 10 spacecraft was received on January 22, 2003; NASA reported that the power source had depleted. Although the spacecraft can no longer speak to us, it presses onward—it now speaks for us. As interstellar courier, it bears the accumulated voice of every human, transcribed in, perhaps, the only common language in all the cosmos. We are but cosmic toddlers just learning how to take our first steps into space, and just learning how to speak to the universe.

Since Pioneer 10 was directed neither to an exoplanet nor a star, contact is extremely unlikely. But if, by the merest happenstance, the spacecraft is intercepted by an alien species, there is at least a chance that the species can interpret our message. In all likelihood however, Pioneer 10 and its plaque will be lost in the immense tranquility of empty space. But in no case was our attempt for naught. Pioneer 10 remains more than just a ghost of a ship, and the plaque is more than a shout into the void. The message we sent to the universe still echoes in our ears. Born from such a mission—one that spans space, time, and perhaps, civilizations—is a new mindset, an otherworldly perspective.

From the vantage of a distant world, our sun will be just another star, and our planet hidden in the radiance of the stellar glow. On such a world—one so distant and different from our own—we have not the slightest indication of what life will be like, how it began, how it evolved. If beings were to emerge, we know not their anatomy nor biology nor psychology, their physical traits, their sensory capabilities, their intellectual sophistication, their disposition; more or less, we are blind to every aspect of their species. They could be different in every way—in ways we have yet to understand or could even imagine. We make numerous assumptions about what life is and what life is not—educated guesses based off a sample size of one. But if, in some form or another, advanced consciousness arises elsewhere in the cosmos, it is possible that those beings will wonder, as we did: What are the lights in the sky? Where did the planets come from? What else is out there? Who else is out there? They may compile a system of knowledge of the cosmos and the laws that govern it; we call this “science.” About this hypothetical species, we know but one thing: the science they develop—the natural laws they discover—if they were to do so, would be exactly the same as our own.

Although not every human conducts science, it is conducted for every human. Science speaks to all of us in a way nothing ever has. It sparks new ideas and alternate perspectives. It brings each of us together and all of us forward. It is, at the very least, an international language, because there is an implied assertion with every question: there is something we do not know; and with our missions, we learn together. We probe the unknown looking for answers, venturing to understand the universe as it is—not the way we want it or believe it to be. Every step of the way, we strive not to fit the universe to the limits of our minds, but stretch our minds to the limitlessness of the universe.  


For every great scientific discovery and technological advancement, there was a time before, when the universe was a little less known. The significance and brilliance of our technologies and the science that drives them is too often overlooked. We forget the time before—a time without cell phones and personal computers, automobiles and airplanes—during which we wondered what it would be like to communicate at the speed of light and fly around to the other side of the planet in a matter of hours. Right now, at this time, we wonder what it would be like to find life elsewhere in the cosmos and to make first contact. This is the time before that great discovery, and there will be a time after. Maybe in the near future, or maybe a more distant one, it will be commonplace to carry on conversations with extraterrestrials; and again, we will forget how, right now, we are ceaselessly wondering, in endless search for an answer.


A Message from Earth, by Carl Sagan, Linda Salzman Sagan, and Frank Drake

The Cosmic Connection, by Carl Sagan


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