Pioneer plaque

During preparations for Pioneer 10, a proposal was made to attach a greeting that could remain with the spacecraft after its planetary mission. Astronomer Carl Sagan and physicist Frank Drake developed the plaque's design, and artist Linda Salzman Sagan prepared its artwork. Similar plaques were installed on Pioneer 10 and Pioneer 11. Their purpose was not to transmit a radio signal but to carry a durable, visual message in case another intelligence ever found either spacecraft.

The plaque combines several diagrams rather than a written message in a particular human language. A schematic of the hydrogen atom provides a reference based on a physical transition and its associated wavelength. A map uses lines from the Sun to selected pulsars—rapidly rotating neutron stars with measurable periods—to indicate the Sun's position in the Galaxy. Another schematic shows the Solar System and the spacecraft's path from it. A male and a female human figure appear beside an outline of the spacecraft, giving a scale comparison and indicating the beings who made it. The diagrams rely on scientific conventions that the designers hoped an unfamiliar observer could infer; their interpretation is not guaranteed.

Pioneer 10 launched on 2 March 1972 and Pioneer 11 on 6 April 1973. Both explored Jupiter, while Pioneer 11 also made a close encounter with Saturn. The plaque was fixed to the spacecraft rather than designed for Earthward transmission, and the probes continued outward after completing their planetary missions. NASA describes the possibility of another civilization finding them as a distant-future prospect. The plaques are therefore both artifacts of early outer-planet exploration and examples of how people have imagined communicating across vastly different cultures and timescales.

The plaque's images are often described as a message to extraterrestrial life, but they cannot ensure shared assumptions about symbols, perspective, or the human body. The pulsar map also depends on astronomical observations being understood in the intended way. The designers sought to anchor the diagrams in physical quantities and astronomical references rather than rely on spoken language, but there is no evidence that the plaque has been encountered or decoded by anyone beyond Earth.