© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

24.3  Extraterrestrial Starprobes and Artifacts

Surprisingly enough, the Arecibo radio pictogram was not mankind’s first intentional space message for ETs. Pioneer 10, a spacecraft, was first.

Pioneer 10 was launched toward Jupiter on 3 March 1972, loaded with scientific equipment designed to measure the radiation environment surrounding the giant planet. Traveling at 11,000 meter/second, the interplanetary probe encountered Jupiter on 4 December 1973 and swung around its massive bulk at close range. Assisted by a kind of "slingshot effect," the spacecraft rapidly accelerated up to 23,000 meter/second. In 1976 it reached the orbit of Saturn, and three years later the orbit of Uranus, where its radio signals finally became too weak for detection from Earth. In 1983 Pioneer 10 will cross the orbit of Pluto and head out into deep space at an interstellar cruising speed of 0.0043%c (13,000 meter/second).³¹³⁶ It will become the first manmade object to leave the solar system, our first interstellar spacecraft.*

Attached to the exterior of the vehicle is a 6" x 9" gold-anodized aluminum plate engraved as shown in Figure 24.10. The message announces our existence to the cosmos. Any alien species which picks it up and deciphers its meaning can tell who built it, when and where it was built, how tall we are, our basic physiology, and our approximate technology at the time of launch.¹⁶⁸

Figure 24.10 Messages from Interstellar Probes: The Pioneer 10 Plaque

Below is a drawing of the engraved gold-anodized aluminum plate which is now hurtling out into inter stellar space at about 0.0043%c, in the general direction of Aldebaran in the constellation Taurus.

The message begins at the top with a schematic representation of the "hyperfine transition" of neutral atomic hydrogen: In going from a state in which the spin of the electron and proton are aligned, to a state in which they are opposed, radio waves at 1.42 GHz are emitted. Since hydrogen is the most abundant element in the universe, and the "hyperfine transition" the most common change of state for hydrogen, it is expected that alien radioastronomers will early detect this radiation and thus understand the significance of the symbols engraved on the plaque. Since a frequency of 1.42 GHz is a wavelength of 21 centimeters, this is adopted as the unit of length by the binary digit designation "1" under the line connecting the hydrogen atom symbol. At the extreme right are depictions of human beings. Next to them are tote marks indicating the binary number eight. Eight times 21 centimeters is 1.68 meters, the average human height. The outline of the Pioneer craft behind them confirms this estimate. Where does the Pioneer craft come from, and when was it launched Curious ETs can answer these questions by carefully examining the plaque. At left of center is some object centered among 15 other objects. Each is labeled with a very long string of binary digits; the only thing that can be known to this accuracy is the period of a pulsar. Since pulsars slow down at known rates, scientists estimate that even 10⁶-10⁸ years after launch, the launch date of Pioneer can be pinpointed by ETs to the nearest century or millennium. The solid line to each pulsar represents its relative distance from Pioneer’s launch point. Using computer analysis, our solar system may be located to within 60 light-years from anywhere in our Galaxy. Our position is specified to 1 of 1000 possible Stars.

As a final aid in locating Sol, the Solar System is sketched along the bottom of the plaque. The path of the Pioneer spacecraft is also shown, emanating from the third planet, then whipping past the fifth and on out into inter stellar space. The distance of each world from the sun is given in binary digits. Finally, the radio dish points back at the third planet as it makes its exit from the system. Clearly, the intelligent beings are there.

A vastly more sophisticated message was affixed to each of the follow-up missions to the jovian worlds in the late 1970’s, called Voyagers 1 and 2.³¹³¹ Instead of a simple plaque, a phonograph record was the chosen medium. The Voyager phonograph record contents are too lengthy to reproduce here but are listed in Table 24.4.

The record is a 12" copper disk to be played at 16 2/3 revolutions/minute using a ceramic cartridge and stylus enclosed for the purpose. Instructions for playback are written in pictorial sign language on the outside of the aluminum can holding the record. Remarks Carl Sagan optimistically: "If they’re able to tool around in interstellar space picking up stray, derelict spacecraft, they ought to be able to figure out our instructions.**

* According to computer projections, Pioneer 10 is creeping out into a relatively empty region of space. Estimates indicate that it should pass fairly close to the star Aldebaran (aTauri), which is 68 light-years from Earth, in the year 1,601,983 A.D.

** Computer projections by Michael B. Helton at JPL show that the Voyagers, like the Pioneers before them, will not closely encounter any alien solar systems. Voyager 1 will pass Pluto’s orbit late in 1987 and head out toward the constellation Ophiuchus (Declination 10.1º, Right Ascension 17h, 20m). Voyager 2, assuming it goes to Uranus but not Neptune, will exit the solar system in mid-1989 on the way to Capricornus (Declination -14.9°, Right Ascension 21h, 1m). In about 40,000 years both craft should coast to within 1.7 light-years (Voyager 1) or 1.1 light-years (Voyager 2) of AC+79 3888, a fourth magnitude star. Voyager 2 should pass a similar distance from another star (AC -24 2833-183) 100,000 years later in Sagittarius, and about 375,000 years after that, Voyager 1 will pass within 1.5 light-years of AM +21 652 in the constellation of Taurus.³²⁰⁷

Last updated on 6 December 2008