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.
History
The original idea, that the Pioneer spacecrafts 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 (now best known for his studies of a purported portrait of a humanoid Martian face and an associated ruined city in the surrounding area), 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, 1973. Both spacecraft left the solar system in the 1980s.
| Material: | 6061 T6 gold-anodized aluminium |
| Width: | 229 mm (9 inches) |
| Height: | 152 mm (6 inches) |
| Thickness: | 1.27 mm (50/1000 inches) |
| Mean depth of engraving: |
0.381 mm (15/1000 inches) |
At the top left of the plate is a schematic representation of the hyperfine transition of hydrogen. 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-1). Both units are used as measurements in the other symbols.
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 x 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.
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 radial pattern on the left of the plaque shows 15 lines emanating from the same origin. 14 of the lines have corresponding long binary numbers which stand for the periods of pulsars. Since these periods will change over time, the epoch of the launch can be calculated from these values.
The lengths of the lines show the relative distances of the pulsars to the sun. A tick mark at the end of each line gives the Z coordinate perpendicular to the galactic plane.
If the plaque is found, only some of the pulsars may be visible from the location of its discovery. Showing the location with as many as 14 pulsars provides redundancy so that the location of the origin can be triangulated even if only some of the pulsars are recognized.
The fifteenth line extends to the right behind the human figures. This line indicates the relative distance to the center of the Galaxy.
At the bottom of the plaque is a schematic diagram of the solar system. A small picture of the spacecraft is shown, and the trajectory shows its way past Jupiter and out of the solar system. Saturn's rings could give a further hint to identifying the solar system.
The binary numbers next to the planets show the relative distance to the sun. The unit is 1/10th of Mercury's orbit.
Critics have argued that it may not be wise to show where the spacecraft originated, because malicious extraterrestrial intelligences could use the information to find and attack the Earth. Dr. Sagan opposes this view, because it is highly unlikely that the message will be found in a near epoch.
Another point of criticism is that the message is too anthropocentric and too hard to understand. Almost none of the human scientists that were shown the message was able to decode all of the message. It can be assumed that it will be even harder for extraterrestrial intelligences that do not share our common knowledge.
According to Sagan (Murmurs of Earth, 1978, New York, ISBN 0679744444), there were many negative reactions to the plaque due to the fact that the human beings were displayed naked. The Chicago Sun Times retouched its image to hide the genitals of the man and woman. The Los Angeles Times received "angry letters" from readers which accused NASA of wasting taxpayer money to send "obscenities" into space.
Feminists complained that only the hand of the man was raised and not that of the woman. In response to this criticism, a similar image included on the Voyager Golden Record showed the woman with her hand raised.
See also Pioneer 10, Pioneer 11, Pioneer program.
Symbology
Hyperfine transition of neutral hydrogen
Hyperfine transition
of hydrogen.
Figures of a woman and a man
A man and a woman.Silhouette of the spacecraft
The Pioneer spacecraft.Relative position of the Sun to the center of the Galaxy and 14 pulsars
14 pulsars with periods.Solar system
The solar system.Criticism of the plaque
External links
