Message from Mankind

Scheduled to begin this week, the journey will be the most spectacular ever undertaken from earth: an odyssey of two years and half a billion miles--including a hazardous stretch through the asteroid belt--to fly to within 87,000 miles of the planet Jupiter. If all goes well, the unmanned ship--Pioneer 10--will radio back the first closeup pictures of the giant planet, probe its intense magnetic fields and radiation belts and perhaps peek at one of the twelve Jovian moons. Then with the planet's powerful gravity acting as a slingshot, Pioneer will be hurled beyond Jupiter to begin the first voyage of a man-made spacecraft out of the solar system.

To Cornell Astronomers Carl Sagan and Frank Drake, Pioneer's flight into interstellar space is not only a scientific adventure but a rare opportunity. Thus they persuaded NASA to attach a unique plaque to Pioneer's antenna supports. Its purpose: to indicate where the far-ranging robot came from and who its builders were should Pioneer ever be intercepted by extraterrestrial beings.

Chance Encounter. That possibility is admittedly small. Traveling at a velocity of seven miles a second, Pioneer could not reach the nearest star in less than 80,000 years and might never fly close to a star orbited by inhabited planets. But the longer the 6 in.-by-9 in. aluminum plaque survives, the better chance there is of such an encounter. To assure its preservation, the plaque has been anodized with erosion-resistant gold. What is more, the symbols etched into it have been designed to be meaningful even to beings totally unfamiliar with human logical processes.

As their central illustration, Sagan and Drake--helped by Sagan's wife, Linda, an artist--chose figures of two representative earthlings (see A in diagram). Their height is indicated by the scale drawing of Pioneer in the background (B). The message contains a more subtle dimensional clue (C) that an extraterrestrial physicist should quickly recognize: an atom of hydrogen, the most abundant element in the universe, which is shown undergoing a change of energy state (indicated by the different orientations of the orbiting electrons on the circles). During this process, the atom gives off a pulse of radiation with a wave length of 21 cm., which is also the message's basic unit of measure. For example, to the woman's right is the binary symbol for eight (D). Multiplied by 21 cm., the figure yields her height, 168 cm., or about 51 ft., which can easily be verified by comparing her size to that of the spacecraft.

Million Years. The message's most ingenious feature, however, is the large starburst pattern (E). Fourteen of the lines symbolize specific pulsars, each recognizable by the precise frequency (also noted in binary terms) at which they give off radio signals. The 15th line (F), extending behind the humans, indicates the distance of their star to the center of the galaxy. That information should tell extraterrestrial scientists even a million years from now when and from where the spacecraft was launched. For specific details, they can look at a representation of the solar system (G). It shows that Pioneer left from the third planet from the sun (lower left), swept past the fifth (Jupiter) and then veered off into interstellar space.

"We do not know if the message will ever be found or decoded," the Sagans and Drake write in Science. "But its inclusion on the Pioneer spacecraft seems to us a hopeful symbol of a vigorous civilization on earth."

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