Guide for extraterrestrials: how to interpret the messages sent in the ‘Pioneer’ and ‘Voyager’

Many know that the Voyager 2 probe, which has just returned to the present day after losing its connection to Earth, carries a message for aliens, who have received a lot of attention in recent days after statements by a confidant in Congress. of the USA that assured that the Pentagon hides “non-human remains” of extraterrestrial origin. What is not so well known is that a total of four planetary probes launched in the 1970s carry messages in case they fall into the hands of an extraterrestrial civilization in the very distant future. It was the brainchild of Eric Burgess, a British consultant who suggested it to Carl Sagan and Frank Drake of the Planetary Society. The two of them were the authors of the basic design of the first postcard sent to our neighbors, explaining who we are and what we do. The initial messages consisted of two identical plates attached to the sides of the Pioneer 10 and 11 probes. They were directed towards Jupiter, although taking advantage of a cosmic carambola, Pioneer 11 also visited Saturn. Those two ships were the first objects to reach the speed to escape the Sun and enter interplanetary space.

For us, the meaning of some elements of the plate are obvious. The two human figures, for example. Based—very loosely—on Greek sculptures and designs by Leonardo, they were heavily criticized in their day. On the one hand, the mixture of multiracial traits and, above all, the censorship that a NASA department imposed when considering the female character too explicit. Also, he told himself, an extraterrestrial would hardly be able to interpret the friendly gesture of the raised hand. But at least that allowed all five fingers to be exposed, with the opposable thumb.

The most important reference are the two circles in the upper left corner. It represents a hydrogen atom in its two states: with the electron in its upper and lower energy levels. When this jump occurs, the atom emits a characteristic radiation of 21 centimeters in wavelength, the most abundant in the universe. An alien should know her. Between the two atoms, a vertical line indicates a binary “one”. 21 centimeters will be the unit to measure the rest of the figures.

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To the right of the woman, two lines indicate her height and between them, the binary number 1000 (one horizontal dash and three vertical ones, that is, 8 in decimal). Eight times 21 centimeters correspond to 1’68 meters. The man is a little taller. Behind, schematically, the profile of the Pioneer, at the same scale. In the lower margin, a schematic of the Solar System, including Pluto, which was still a planet. The trajectory followed by the ship is indicated, highlighting the gravity assist maneuver when passing Jupiter, which is what gave it the escape velocity. Its antenna points towards the third little circle: the Earth.

The Pioneer plates (1972-1973), a kind of interstellar “message in a bottle”, were designed and popularized by American astronomer and science writer Carl Sagan and Frank Drake.

Next to each planet, a number in base 2 gives its distance from the Sun. The unit of scale here is not the radiation from hydrogen, but one-tenth the distance from Mercury. Above it appears the binary 1010, or 10. Pluto is 1111111100 times further away. If the aliens are able to crack this enigma, they will undoubtedly be very intelligent.

And where are we? The key is given by the dashed star to the left of the two figures. The longer horizontal line suggests the distance from the Sun to the center of the galaxy. The other fourteen show the directions of as many pulsars, a kind of cosmic lighthouses characterized by their regular and rapid flashes. The long binary numbers indicate the period of each (again, taking the hydrogen transition as the unit). Since the plate was flat, the third dimension is given by the length of the line, proportional to the height of the pulsar above the galactic plane. With this information, any alien could triangulate and deduce the location of the Sun among the millions of stars in the Milky Way. A trivial task, no doubt, or at least so its authors believed.

A few years after the Pioneers, the two Voyager probes carried a much more sophisticated message on board: a vinyl-like record, accompanied by a capsule to play it. Like the plate, it was covered by a thin layer of gold that was to protect it during the eons of its journey.

The disc contained photos and sounds: images of the Earth, both from orbit and landscapes, fauna and flora. Human anatomy charts, world map showing continental drift, Sydney Opera House and the Gold Gate (duly annotated in binary to indicate its longitude), Bali dancers, the UN building (by day and illuminated at night), the Taj Mahal, a supermarket, a finish line for the 100 meter dash, Jane Goodall with her chimpanzees, a page from Newton’s Principia and the score of a Beethoven Cavatina.

The ‘Voyager’ gold record (1977) has all the basic information to play it and the galactic coordinates to find Earth.

In total, 116 images. One of them (number 78), which showed a diver and a fish, could never be published due to a failure to reach an agreement with the author on the copyright issue. In its own way, that absence also provides interesting reflections on our society.

The audio section was made up of greetings in fifty languages, from ancient Sumerian (which only a couple of hundred academics speak) to Mandarin or Telugu, typical of central India. Instead, there was no Swahili; the announcer who was supposed to participate forgot the appointment and did not show up at the recording session.

Other recordings will pose performance problems for any alien: a volcano eruption, crickets and frogs, Morse beeps, the striking of two flint stones, a ship’s siren, or the soft sound of a kiss. And also the wave of an electroencephalogram in full meditation. Perhaps, it was said, a sufficiently advanced civilization will be able to interpret it and read our thoughts.

There was already a music section: three pieces by Bach (there were those who proposed including his complete work, but the idea was discarded because “it would have been showing off”). And orchestral samples from Java, pygmy coming-of-age songs, mariachis, a Louis Armstrong blues and Chuck Berry’s Johnny B. Good; the aria of Mozart’s Queen of the Night, the first movement of Beethoven’s Fifth Symphony together with Navajo songs, Peruvian flutes or a fragment of Stravinsky’s Rite of Spring. Here Comes the Sun by the Beatles should have been included, but the record company that owned the rights denied their authorization.

Instructions on how to play the record were engraved on its surface: like the Pioneers, they showed the scale based on the transitions of the hydrogen atom and the pulsar map. Also, a view of the disk in plan and profile, with the capsule installed on it. In binary, the speed (3.6 seconds per lap, that is, 16 rpm) and a sample of the signals that it had to generate, as well as the duration of each image (8 milliseconds). Finally, two rectangles presented a schematic of the electronic scan on the screen (to be provided by the aliens) and, if all went well, the first calibration image: a perfect circle.

Voyager 1 will pass close to the star Gliese 445 in 44,000 years; its twin, a couple of light years from Ross 248, in 33,000 years. If no one picks them up there, they will continue their journey. Statistics suggest that every 50,000 years they should approach one or another star before getting lost in the swarm of the Milky Way.

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