Pioneer 10/11 Plaque

By Patrick Mondout/NASA

A plaque was placed on both Pioneer 10 and Pioneer 11 with the hope that some alien civilization will encounter the craft at some point and learn something of mankind. On the plaque a man and woman stand before an outline of the spacecraft. The man's hand is raised in a gesture of good will. The physical makeup of the man and woman were determined from results of a computerized analysis of the average person in our civilization.

The key to translating the plaque lies in understanding the breakdown of the most common element in the universe - hydrogen. This element is illustrated in the left-hand corner of the plaque in schematic form showing the hyperfine transition of neutral atomic hydrogen. Anyone from a scientifically educated civilization having enough knowledge of hydrogen would be able to translate the message. The plaque was designed by Dr. Carl Sagan and Dr. Frank Drake and drawn by Linda Salzman Sagan.

		A diagram describing the images on the plaque. The usual suspects criticized the use of nude humans as immoral (let's hope the aliens are more enlightened).
		NASA image

Official NASA Statement

The Pioneer 10 spacecraft, destined to be the first man-made object to escape our solar system, carries this plaque. It is designed to show scientifically educated inhabitants of some other star system-who might intercept it millions of years from now-when Pioneer was launched, from where, and by what kind of beings. The design is engraved into a gold-anodized aluminum plate, 152 by 229 millimeters (6 by 9 inches), attached to the spacecraft's antenna support struts in a position to help shield it from erosion by interstellar dust.

At the far right, the bracketing bars (1) show the height of the woman compared to the spacecraft. The figure indicated by (2) represents a reverse in the direction of spin of the electron in a hydrogen atom. This transition puts out a characteristic radio wave 21 cm long, so we are indicating that 21 cm is our base length. The horizontal and vertical ticks (3) are a representation of the number 8 in binary form. Therefore, the woman is 8 x 21 cm = 168 cm, or about 5'5" tall. The human figures represent the type of creature that created Pioneer. The man's hand is raised in a gesture of good will.

The radial pattern (4) will help other scientists locate our solar system in the galaxy. The solid bars indicate distance, with the horizontal bar (5), denoting the distance from the Sun to the galactic center. The shorter solid bars represent directions and distances to various pulsars from our Sun, and the ticks following them are the periods of the pulsars in binary form. Pulsars are known to be slowing down and if the rate of slowing is constant, an other-world scientist should be able to roughly deduce the time Pioneer was launched. Thus, we have placed ourselves approximately in both space and time. The drawing at the bottom (6) indicates our solar system. The ticks accompanying each planet are the relative distance in binary form of that planet to the Sun. Pioneer's trajectory is shown as starting from the third planet, Earth.

Sources: NASA and selected books below.