Symbolism

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.

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 (1000, with a small defect in the first zero). 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 this gesture may not be understood, it offers a way to show the opposable thumb and how the limbs can be moved.

Originally Sagan drew the humans holding hands, but soon realized that an extraterrestrial might perceive the figure as a single creature rather than two organisms. The figures appear to be white and Occidental, but the generic depiction of humankind was intended to be as racially ambiguous as possible.

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.

But Sagan himself wrote that "The decision to omit a very short line in this diagram was made partly because conventional representation in Greek statuary omits it. But there was another reason: Our desire to see the message successfully launched on Pioneer 10. In retrospect, we may have judged NASA's scientific-political hierarchy as more puritanical than it is. In the many discussions that I held with such officials up to the Administrator of the National Aeronautics and Space Administration and the President's Science Adviser, not one Victorian demurrer was ever voiced; and a great deal of helpful encouragement was given."

He also commented that "The idea of government censorship of the Pioneer 10 plaque is now so well documented and firmly entrenched that no statement from the designers of the plaque to the contrary can play any role in influencing the prevailing opinion. But we can at least try."

Relative position of the Sun to the center of the Galaxy and 14 pulsars with their periods denoted

The radial pattern on the left of the plaque shows 15 lines emanating from the same origin. Fourteen of the lines have corresponding long binary numbers, which stand for the periods of pulsars, using the hydrogen spin-flip transition frequency as the unit. 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 data for one of the pulsars is misleading. When the plaque was designed, the frequency of pulsar "1240" (now known as J1243-6423) was known to only three significant decimal digits: 0.388 seconds. The map lists the period of this pulsar in binary to much greater precision: 100000110110010110001001111000. Rounding this off at about 10 significant bits (100000110100000000000000000000) would have provided a hint of this uncertainty. This pulsar is represented by the long line pointing down and to the right.

The fifteenth line on the plaque extends to the far right, behind the human figures. This line indicates the sun's relative distance to the center of the galaxy.

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. Both Pioneers 10 and 11 have identical plaques; however, after launch, Pioneer 11 was redirected towards Saturn and from there it exited the solar system. In this regard the Pioneer 11 plaque is somewhat inaccurate. The Saturn flyby of Pioneer 11 would also greatly influence its future direction and destination as compared to Pioneer 10 but this fact is not depicted in the plaques.

Saturn's rings could give a further hint to identifying the solar system. Rings around the planets Jupiter, Uranus and Neptune were unknown when the plaque was designed. Pluto was considered to be a planet when the plaque was designed; in 2006 the IAU reclassified Pluto as a dwarf planet and then in 2008 as a plutoid.
The binary numbers next to the planets show the relative distance to the sun. The unit is 1/10 of Mercury's orbit.

Silhouette of the spacecraft

Behind the figures of the human beings, the silhouette of the Pioneer spacecraft is shown in the same scale so that the size of the human beings can be deduced by measuring the spacecraft.