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Pioneer plaque

On board the unmanned spacecraft Pioneer 10 and Pioneer 11 is a plaque with a pictoral 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 spacecrafts. 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.

The plaque on board the Pioneer spacecrafts
Enlarge
The plaque on board the Pioneer spacecrafts

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.

Contents

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.

Physical properties

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)

Symbology

Hyperfine transition of neutral hydrogen

Hyperfine transition of hydrogen
Hyperfine transition
of hydrogen.

At the top left of the plate is a schematic representation of the hyperfine transition of hydrogen, which is a very 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.

Figures of a woman and a man

A man and a woman
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.

Silhouette of the spacecraft

The Pioneer spacecraft
The Pioneer spacecraft

The Pioneer spacecraft.

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.

Relative position of the Sun to the center of the Galaxy and 14 pulsars

14 pulsars with periods
14 pulsars with periods.

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.

Solar system

The solar system
The solar system

The solar system.

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.

Criticism

Critics have argued that the message is too anthropocentric and too hard to understand. Although the message was designed to encode the most information possible in minimal space, rather than to be easily readable, almost none of the human scientists that were shown the message were able to decode all of it. It can be assumed that it will be even harder for extraterrestrial intelligences that do not share our common knowledge. If it ever would be found, it is expected that the finders will spend generations deciphering it, much like deciphering the Egyptian hieroglyphs took centuries.

Another point of criticism is 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.

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 that accused NASA of wasting taxpayer money to send "obscenities" into space.

Furthermore, 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. (Alan Fletcher, "The art of looking sideways")

The fact that the man is the one doing the greeting on behalf of the woman and the rest of humanity was criticised as sexist by feminist groups. A similar image subsequently encoded on the Voyager Golden Record showed the woman giving the greeting.

See also Pioneer 10, Pioneer 11, Pioneer program.

External links

Last updated: 05-07-2005 03:35:06
Last updated: 05-13-2005 07:56:04