IN A HIGH VACUUM Pioneer 10 gleamed under the harsh lights of an artificial Sun in the space simulator at TRW Systems, California, its final tests underway prior to shipment to Kennedy Space Center. A group of science correspondents from the national press were at TRW Systems for a briefing on Pioneer and had been invited to see the spacecraft under test.
Looking at Pioneer through the portholes of the simulator, one of the correspondents, Eric Burgess, then with The Christian Science Monitor, visualized the passage of Pioneer 10 beyond the Solar System as mankind's first emissary to the stars. This spacecraft should carry a special message from mankind, he thought, a message that would tell any finder of the spacecraft a million or even a billion years hence that planet Earth had evolved an intelligent species that could think beyond its own time and beyond its own Solar System.
He mentioned this to Richard Hoagland, a freelance writer, and Don Bane, then with the Los Angeles Herald-Examiner, and they enthusiastically agreed. The result was that Burgess and Hoagland approached Dr. Carl Sagan, Director of the Laboratory of Planetary Studies, Cornell University, who was then visiting the Jet Propulsion Laboratory, Pasadena, in connection with Mariner 9. Dr. Sagan had a short while earlier been involved in a conference in the Crimea devoted to the problems of communicating with extraterrestrial intelligences, and together with Dr. Frank Drake, Director of the National Astronomy and Ionosphere Center, Cornell, had designed one type of message that might be used to communicate with an alien intelligence.
Dr. Sagan also was enthusiastic about the idea of a message on Pioneer. He and Dr. Drake designed a plaque, and Linda Salzman Sagan prepared artwork which was presented to the National Aeronautics and Space Administration which accepted it for this first spacecraft from the Solar System into the Galaxy.
The plaque design was etched into a gold anodized aluminum plate, 15.25 by 22.8 cm  (6 by 9 inches), and 0.127 cm (0.050 inches) thick. This plate was attached to the spacecraft's antenna support struts in a position to help shield it from erosion by interstellar dust (Figure Ep-1 ).
When Pioneer 10 flew by Jupiter it acquired sufficient kinetic energy to carry it completely out of the Solar System. About 40,000 years hence it will have coasted to the distance of the nearest star, heading in the direction of the constellation of Taurus, the Bull. Somewhere between one and ten billion years from now it may pass through the planetary system of a remote stellar neighbor, one of whose planets may have evolved intelligent life.
If that life possesses sufficient intelligence to detect the Pioneer spacecraft needing a higher technology than mankind possesses today-it may also have the curiosity and the technical ability to pick up the spacecraft and take it into a laboratory to inspect it. Then the plaque with its message from Earth people should be found and hopefully deciphered.
The plaque tells of Man, where and when the species lived, and its biological form. At top left of the plaque (Figure Ep-2) is a schematic of the hyperfine transition of neutral atomic hydrogen-a universal 'yardstick'-providing a basic unit of both time and physical length throughout the physical universe. As a further size check, the binary equivalent of the decimal number 8 is shown between tote marks indicating the height of the two human figures to be compared with the scale of the spacecraft itself which is also shown in line silhouette on the plaque.
The hydrogen wavelength about 20.32 cm (8 inches) - multiplied by the binary number representing 8 alongside the woman, gives her height, namely 62.56 cm (64 inches).
The radial pattern to the left of the center of the plaque represents the position of the Sun relative to 14 pulsars and to the center of the Galaxy. The latter direction is indicated by the long horizontal line with no binary digits on it. The binary digits on the other lines denote time. This can be deduced because they represent precision to...
....10 decimal digits, which is unlikely for distances to stellar objects but quite feasible for measurements of time. And from the unit of time established from the hydrogen atom, the extraterrestrial intelligence should be able to deduce that all the times are about one tenth of a second . . . pulsars!
Since the periods of pulsars run down at well established rates they act as galactic clocks. An advanced civilization would be able to search its galactic records and identify the star system from which the spacecraft originated, even if Pioneer is not intercepted for several billions of years.
Below the orientation diagram, as a further aid to identification should the spacecraft be intercepted while our Solar System is still in the galactic records, there is a diagram showing relative distances of the solar planets and identifying the ringed planet Saturn and the planet from which Pioneer originated. After accelerating past the largest planet as shown by a track, the spacecraft is depicted with its antenna pointing back to its origin on the third planet.
 Finally the plaque depicts man and woman in what to humans is a characteristic gesture of friendliness but also shows how limbs can be moved and displays the important four fingers and opposing thumb. The figures and physiognomy were carefully chosen and drawn for ethnic neutrality, and no attempt is made to explain to an alien intelligence what may be mysterious differences between two physical types-man and woman.
A similar plaque is carried by Pioneer 11.
As an epilog to the Pioneer mission to Jupiter, the plaque is more than a cold message to an alien life form in the most distant future. It signifies an attribute of mankind that in an era when troubles of war, pollution, clashing ideologies, and serious social and supply problems plague them, men can still think beyond themselves and have the vision to send a message through space and time to intelligence on a star system that perhaps has not yet condensed from a galactic nebula.
The plaque represents at least one intellectual cave painting, a mark of Man, that might survive not only all the caves of Earth, but also the Solar System itself. It is an interstellar stela that shows mankind possesses a spiritual insight beyond the material problems of the age of human emergence.