The Pioneer and Voyager spacecraft famously contain messages to anyone who might someday find them. Both Pioneers carry a plaque, while the Voyagers carry a phonograph record. An enormous amount of effort went into creating these objects, but could an alien observer truly understand the messages we have sent to the stars? While we cannot take anything for granted when it comes to how these messages might or might not be interpreted, let’s assume that the beings who might find the spacecraft can at least see or hear with eyes or ears similar to our own. Each message was designed with not only the information it was to carry in mind, but also the means to establish understanding through common denominators found throughout the universe. The Pioneer plaque Pioneer 10 and 11 each carry a 6 x 9-inch (15 x 23 centimeters), gold-anodized aluminum plaque. The plaque is affixed to support struts close to the spacecraft’s bus (main body). Carl Sagan and Frank Drake played key roles in designing the plaque and Linda Salzman Sagan, Sagan’s wife at the time, was the artist who actually drew the images engraved on the plaque.

NASA Ames Resarch Center (NASA-ARC)

The most striking feature of the plaque are the figures of the man and the woman overlying the silhouette of the Pioneer spacecraft itself. While this does clearly convey our physical size and shape, as well as that sexual dimorphism is present in humans, the facial features of the couple have little detail and the sort of sensory organs are being depicted (the couple’s ears are barely shown at all) might be unclear. The man and woman both have their mouths closed, and viewers might not understand that these are even mouths at all. Given how the image is drawn, an observer could also be forgiven for not understanding that both the male and female have hair on their heads.



The couple both have a bland expression (which may have been an attempt to avoid anything that could be interpreted as hostile) and the man is seen raising his right hand with the palm facing the viewer. While this gesture clearly conveys a greeting when viewed by another human, an extraterrestrial may have no way of interpreting this gesture. (Could you interpret a gesture made by an antelope … or a praying mantis?) It does show, however, that humans have opposable thumbs, as well as the general range of motion of the upper limbs.



With regards to the scientific data presented, the top left of the plaque shows the hyperfine transition of neutral hydrogen as a means of conveying to the reader baseline units of time (0.7 nanoseconds, the frequency of the transition) and distance (21 cm, the wavelength of the light released by the transition). If one is able to deduce that the image is that of hydrogen, the time and distance should be understandable.



The plaque also contains a map of our Sun relative to 14 pulsars as well as the center of our galaxy, conveying both the distances to the pulsars and their frequency in binary notation. As this image conveys copious objective data, a spacefaring species might well be able to easily interpret it.



Finally, the plaque contains a map of the solar system. The solar system map is likely among the more easily interpreted parts of the plaque, with Pioneer shown to have originated from the third planet. The plaque was created at a time when Pluto was still considered the ninth planet (before the discovery of other trans-Neptunian dwarf planets such as Eris and Sedna, among others), but it would still direct the reader’s attention to Earth if they were able to figure out that our solar system was the one depicted.