Carl Sagan «Pioneer Plaque» 1972.
Plaque in position on the Pioneer space vehicle.
On board each of the unmanned spacecraft Pioneer 10 and Pioneer 11 is a plaque with a pictorial message from mankind. The plaque shows the figures of a man and a woman along with several symbols that are designed to provide information about the origin of the spacecraft. It serves as a kind of interstellar "message in a bottle". However, it is very unlikely that it will ever be found. The mean time for the spacecraft to come within 30 astronomical units of a star is longer than the current age of the galaxy.
Material: 6061 T6 gold-anodized aluminium
Width: 229 mm (9 inches)
Height: 152 mm (6 inches)
Thickness: 1.27 mm (0.05 inches)
Mean depth of engraving: 0.381 mm (0.015 inches)
Hyperfine transition of neutral hydrogen.
At the top left of the plate is a schematic representation of the hyperfine transition of hydrogen, which is the most abundant element in the universe. Below this symbol is a small vertical line to represent the binary digit 1. This spin-flip transition of a hydrogen atom from electron state spin up to electron state spin down can specify a unit of length (wavelength, 21 cm) as well as a unit of time (frequency, 1420 MHz). Both units are used as measurements in the other symbols. Note that since the plaque is 22.9 cm wide, the actual unit of length could have been depicted.
Figures of a man and a woman.
On the right side of the plaque, a man and a woman are shown in front of the spacecraft. Between the brackets that indicate the height of the woman, the binary representation of the number 8 can be seen. In units of the wavelength of the hyperfine transition of hydrogen this means 8 × 21 cm = 168 cm.
The right hand of the man is raised as a sign of good will. Although it is unlikely that this gesture is truly universal, it offers a way to show the opposable thumb and that the limbs can be moved.
One can see that the woman's genitals are not really depicted; only the mons veneris is shown. It has been claimed that Sagan, having little time to complete the plaque, suspected that NASA would have rejected a more intricate drawing and therefore made a compromise just to be safe. However, according to Mark Wolverton's more detailed account, the original design included a "short line indicating the woman's vulva". It was erased as condition for approval by John Naugle, former head of NASA's Office of Space Science and the agency's former Chief Scientist.
Silhouette of the Pioneer spacecraft relative to the size of the humans.
Behind the figures of the human beings, the silhouette of the Pioneer spacecraft can be seen. It is displayed in the same scale so that the size of the human beings can be deduced from measuring the spacecraft.
The Pioneer spacecraft were the first man-made objects to leave the solar system. The plaque is attached to the antenna support struts in a position that shields it from erosion by stellar dust. NASA expects the plaque (and the craft itself) to survive longer than the earth and its sun.
The original idea, that the Pioneer spacecraft should carry a message from mankind, was first mentioned by Eric Burgess when he visited the Jet Propulsion Laboratory, Pasadena during the Mariner 9 mission. Together with Richard Hoagland he approached Dr. Carl Sagan who had lectured about communication with extraterrestrial intelligences at a conference in Crimea.
Dr. Sagan was enthusiastic about the idea of sending a message with the Pioneer spacecraft. NASA agreed to the plan and gave him three weeks to prepare a message. Together with Dr. Frank Drake he designed the plaque and the artwork was prepared by his wife Linda Salzman Sagan. In recent years, Hoagland has attempted to take some credit for the actual design. This claim was strongly denied by both Sagan and Drake, who limit his input only to the idea that there should be some kind of message on the spacecraft.
The first plaque was launched with Pioneer 10 on March 2, 1972, and the second followed with Pioneer 11 on April 5, 1972. Both spacecraft left the solar system in the 1980s.