Murmurs of Earth

by Carl Sagan

  In 1974 a small satellite with a heart of solid brass was launched into a very high, very circular orbit around the Earth. It has external facets which make it look something like a giant golf ball. This satellite is called LAGEOS, an acronym for Laser Geodynamic Satellite. One of its jobs is to measure continental drift on Earth, which typically occurs at the very slow rate of an inch per century. To make such precision measurements, LAGEOS must be placed in an extremely stable orbit, which is the reason for the heart of brass and the high trajectory. Compared to other satellites it is impervious to the pressure of sunlight, the drag of the atmosphere and other factors that tend to cause a rapid decay of satellite orbits. Laser transmitters on the continents of Earth will measure with extremely high accuracy their separation each year by bouncing laser signals off LAGEOS. As time goes on, their separation will change.

  The estimated lifetime of LAGEOS before it burns up in the Earth’s atmosphere is eight million years. This is sufficiently far in our future that a great deal of information may be lost between now and then—including information on the epoch and purpose of LAGEOS itself. For this reason the National Aeronautics and Space Administration asked me to design a small metal plaque to be affixed to LAGEOS as a kind of a greeting card to our remote descendants. Briefly, the card says, in effect: “A few hundred million years ago the continents were all together, as in the top drawing. At the time LAGEOS was launched the map of the Earth looks as in the middle drawing. Eight million years from now, when LAGEOS should return to Earth, we figure the continents will appear as in the bottom drawing. Yours truly.” A picture of the LAGEOS plaque appears on this page, and more information on it in Appendix A.

  The LAGEOS plaque is a time capsule containing extremely limited information intended for the year 8,000,000. It is, like all such spacecraft messages, hitchhiking: the spacecraft is designed for one purpose and the plaque attached (almost always at the last minute) for another purpose. But it is pinpointed for a time in the future far more remote than any attempted before the advent of space flight.

  The first detailed and close-up study of Jupiter, Saturn, their twenty or so moons, and the exquisite rings of Saturn is to be made by the Voyager mission. These two spacecraft, formerly called Mariner Jupiter/Saturn, were launched in the summer of 1977, arrive in the Jupiter system in 1979 and in the Saturn system in 1980/1981. One of the Voyagers may, depending on what happens near Saturn in 1981, continue on to explore the system of the planet Uranus. Like Pioneers 10 and 11, the Voyager spacecraft are so accelerated by their close passage by Jupiter, the most massive planet in the solar system, that they will be ejected out of the solar system, and will, like the Sun and the nearby stars, orbit the massive center of the Milky Way galaxy once every quarter billion years, essentially forever. Just as with Pioneers 10 and 11, it seemed a pleasant and hopeful prospect to place some message for a possible extraterrestrial civilization aboard the Voyager spacecraft, and in December 1976, while I was in Pasadena, California, for the mission operations of the Viking spacecraft on Mars, the Voyager project manager, John Casani, asked me to organize the effort to place an appropriate message aboard the two Voyager vehicles.

  The plaque aboard the LAGEOS spacecraft, designed by Carl Sagan for the inhabitants of Earth 8 million years from now.

  My first thought was to make a modest extension of the Pioneer 10 and 11 plaque, perhaps adding some information from molecular biology—for example, on the structure of our proteins and nucleic acids. I organized a small group of scientific consultants to provide advice on the message contents, including Philip Morrison, professor of physics at Massachusetts Institute of Technology; Frank Drake, professor of astronomy and director of the National Astronomy and Ionosphere Center at Cornell; A. G. W. Cameron, professor of astronomy at Harvard; Leslie Orgel of the Salk Institute for Biological Research; B. M. Oliver, vice-president for research and development at the Hewlett-Packard Corporation; and Steven Toulmin, professor of philosophy and social thought at the University of Chicago. Because some science-fiction writers with backgrounds in the sciences have been thinking about such problems longer than most of the rest of us, I also queried my friends Isaac Asimov, Arthur Clarke and Robert Heinlein. A few other scientists were asked to help but were prevented by their schedules.

  Many of the consultants emphasized that receipt of the message by an extraterrestrial civilization was chancy at best, while its receipt by the inhabitants of Earth was guaranteed: the public would eventually have access to the message contents, as is in fact accomplished by this book. As Oliver put it, “There is only an infinitesimal chance that the plaque will ever be seen by a single extraterrestrial, but it will certainly be seen by billions of terrestrials. Its real function, therefore, is to appeal to and expand the human spirit, and to make contact with extraterrestrial intelligence a welcome expectation of mankind.” Heinlein proposed that Voyager be equipped with a radar corner reflector so that it could be easily found by some future generation of fast terrestrial spacecraft, which could overtake and heave to this ancient derelict. In a telephone message from Sri Lanka on January 3, 1977, Arthur Clarke recommended that the plaque contain a message to our remote descendants saying, “Please leave me alone; let me go on to the stars,” which he supported as, among other things, a statement of hope that our civilization would continue long enough for that message to be read.

  Cameron proposed that the plaque be painted with a coating of natural uranium whose decay products would give the recipients a rough estimate of the length of time that had elapsed since it was launched. Toulmin warned against the tendency in all such time-capsule messages to represent human beings as individuals without stressing the importance of community for the human species. He urged that we include some representation of human beings in communities, cooperating together. Several of the scientists suggested that since the spacecraft itself contains so much information on our technology and physical sciences, at least implicitly, the explicit message ought to be oriented in some other direction.

  Orgel thought there should be some schematic indication—perhaps wavy lines—that Earth is a water-covered planet, and some indication of the molecular basis of terrestrial biology. The laws of physics are, we already know, the same everywhere in the Galaxy, but the molecules making up living beings may be very different elsewhere than on Earth. Some information on our nucleic acids and proteins might be considered very valuable by a recipient civilization. Several consultants urged that we send information other than scientific. Philip Morrison proposed sending the famous Leonardo da Vinci drawing of a man with arms outstretched and some comparable piece of Oriental art. Oliver proposed that behind a Voyager plaque, in a can, we send a magnetic tape, compatible with the tape recorder on the spacecraft, containing the Beethoven Ninth Symphony, or, if the lifetime of the magnetic pattern on the tape would be too short, a comparable wire recording.

  In late January 1977, the American Astronomical Society and its Division for Planetary Sciences were both meeting in Honolulu. As retiring chairman of the DPS I was required to be at this meeting, and as a new member of the council of the parent society, my Cornell colleague Frank Drake was there as well. At the Kawabata Cottage of the Kahala Hilton, Drake made the critical suggestion that determined the subsequent course of the project—namely, that we send a long-playing phonograph record. Because sound information in such a record is physically etched in the record grooves, the information could last for very long times, comparable to or greater than the time for the spacecraft to venture to the stars. This avoided the problem about the lifetime of magnetic tape recordings. In addition, pictures could be encoded in the audio spectrum on such a record, so we could send in the same physical space aboard Voyager many more pictures than we could on a plaque of the Pioneer 10 or LAGEOS sort. I later discovered that 1977 was the hundredth anniversary of the invention of the phonograph record by Thomas Edison (although the original version was a tinfoil disc), so a record would provide a fitting commemoratio
n. (It also transpired, to our great regret, that the inventor of the long-playing record, Peter Goldmark, died in an automobile accident in 1977; the Voyager record can also be considered a memorial to his engineering genius.) Thus, each Voyager spacecraft has a golden phonograph record in a silvery aluminum cover affixed to the outside of its central instrument bay. Instructions for playing the record, written in scientific language, are etched on the cover. A cartridge and stylus, illustrated on the cover, are tucked into the spacecraft nearby. The record is ready to play.

  I was delighted with the suggestion of sending a record for a different reason: we could send music. Our previous messages had contained information about what we perceive and how we think. But there is much more to human beings than perceiving and thinking. We are feeling creatures. However, our emotional life is more difficult to communicate, particularly to beings of very different biological make-up. Music, it seemed to me, was at least a creditable attempt to convey human emotions. Perhaps a sufficiently advanced civilization would have made an inventory of the music of species on many planets and, by comparing our music with such a library, might be able to deduce a great deal about us. I was impressed by a paper by Sebastian von Hoerner of the National Radio Astronomy Observatory in Greenbank, West Virginia, which proposed that the physics of sound permitted only a very limited number of musical forms. Perhaps there is a “universal” music. In addition, I was cheered by an earlier remark of the biologist Lewis Thomas, president of the Sloan-Kettering Institute in New York City. When asked what message he would send to other civilizations in space, Thomas replied with words to this effect: “I would send the complete works of Johann Sebastian Bach.” “But that,” he added as an aside, “would be boasting.”

  The connection between mathematics and music has been marked at least since the time of Pythagoras. Harmony has a distinct mathematical character, and it is a commonplace that mathematicians and theoretical physicists are often also talented in musical composition and performance. Einstein’s passion for the violin is no isolated example. But so far as we can tell, mathematical relationships should be valid for all planets, biologies, cultures and philosophies. We can imagine a planet with uranium hexafluoride in the atmosphere or a life form that lives mostly off interstellar dust, even if these are extremely unlikely contingencies. But we cannot imagine a civilization for which one and one does not equal two or for which there is an integer interposed between eight and nine. For this reason, simple mathematical relationships may be even better means of communication between diverse species than references to physics and astronomy. The early part of the pictorial information on the Voyager record is rich in arithmetic, which also provides a kind of dictionary for simple mathematical information contained in later pictures, such as the size of a human being. Because of the relation between music and mathematics, and the anticipated universality of mathematics, it may be that much more than our emotions are conveyed by the musical offerings on the Voyager record.

  Some months after the Voyager records were launched into space, a science-fiction movie called Close Encounters of the Third Kind was released, portraying physical rather than radio contact between an advanced extraterrestrial civilization and us. Unlike the Voyager case, the extraterrestrials are imagined to visit the Earth, rather than a representative of Earth traversing interstellar space. Despite a credulous acceptance of several stories about unidentified flying objects, the movie had at least one virtue: the initial messages were naive, but at least mathematical (showing the geographical coordinates of a future meeting) and musical. Indeed, the climactic scene in the motion picture portrays a kind of fugue between terrestrial and extraterrestrial electronic organs.

  I made contact with Tom Shepard, vice-president, Red Seal Division, RCA Records, and established Red Seal’s willingness to help us with the early stages of the technical end of the record design. The pressing of an ordinary vinyl twelve-inch long-playing record is made from a mold, which in turn is made from a copper or nickel positive master called a “mother.” Since the technology for such an engraving was in hand, it seemed ideal to send a mother to the stars. Its resistance to erosion in space would be considerably greater than an ordinary vinyl record’s. Because nickel is ferromagnetic, a nickel mother might interfere with the delicate magnetic field detection experiments of Voyager, so a copper mother was settled upon. By this time, in February and March 1977, because we were thinking of a record to be played at the conventional 33⅓ revolutions per minute, we contemplated something like twenty-seven minutes of playing time on a side, or fifty-four minutes altogether. One side would contain music, and the other the non-musical information—for example, pictures.

  But what music? Twenty-seven minutes is barely enough for two movements of a single symphony. How could we send something representative of the music of the planet Earth with its full range of emotion tone and cultural diversity in twenty-seven minutes? I asked for help from many sources. Jonathan Cott, an editor of Rolling Stone, and Ann Druyan, a writer, suggested I contact Robert E. Brown, the executive director for the Center for World Music in Berkeley, and Alan Lomax, director of the Cantometrics Project of Columbia University in New York City. Brown’s recommendations are reprinted in Appendix C, and his comments represent the first coherent statement we received on possible organizing principles for the diversity of human music to be included. Another early set of recommendations—this by Jon Lomberg of the Canadian Broadcasting Corporation—appears in table form in Appendix D. Murry Sidlin, then the resident conductor of the National Symphony Orchestra in Washington and now the musical director of the New Haven Symphony Orchestra and Tulsa Philharmonic, made a number of proposals both for Western classical music and for music of other cultures, including the happy notion of following the last 4½ minutes of Stravinsky’s Rite of Spring with the Prelude and Fugue in C, No. 1, from Book 2 of Bach’s Well-Tempered Clavier. He noted that the emotional contrast would be striking.

  Brown’s recommendation was for thirty-eight minutes of music, and he clearly would have preferred more. Sidlin stressed the importance of including complete musical selections rather than fragments; and this, especially for Western classical music, would greatly increase the musical time required. Lomberg, independently of Lewis Thomas, felt that a number of pieces by the same composer or a number of pieces in the same form, such as the fugue, would illuminate our music and our intent.

  Alan Lomax has devoted his life to recording the ethnic music of the world and to saving it from obscurity and neglect. His Cantometrics Project has developed a computerized classification of virtually all recorded musical styles. We finally made contact with him after his return from an extensive trip abroad. Most of the music on the Voyager record that is not in the Eastern or Western classical traditions was recommended to us by Lomax. He was a persistent and vigorous advocate for including ethnic music at the expense of Western classical music, and the pieces he brought to our attention were so compelling and beautiful that we acceded to his suggestions more often than I would have thought possible. There was, for example, no room for Debussy among our selections, because Azerbaijanis play bagpipes and Peruvians play panpipes and such exquisite pieces were recorded by ethnomusicologists known to Lomax.

  Like Robert Brown, Alan Lomax had a proposed master list of music to include, which we only partially accommodated. After many decades of work, Lomax believes that different stages in the social, economic and technological development of civilization are characteristically reflected by certain styles of music—for example, hunter music, gatherer music, agricultural music, and so on. When Lomax first played Valya Balkanska’s soaring Bulgarian shepherdess’ aria for Ann, she was moved to spontaneous dance. “Do you hear that, honey?” he drawled, grinning and leaning forward. “That’s Europe. That’s the first people who had enough to eat.” If Lomax’s ideas are correct, it might have been possible to communicate something of the evolution of human civilizations through musical motifs alone. But time and other
pressures prevented us from giving a full critical hearing to his proposals. (Just as there are today many workers in wildlife conservation dedicated to noting and preserving endangered species, so Lomax has dedicated his life to preserving endangered folk and ethnic music. His Cantometrics Project is clearly operating on a shoestring budget and deserves much wider attention and support. We are particularly grateful to him for his help in broadening our transcultural musical perspectives, as well as in substantially enhancing the beauty of the Voyager record’s musical offerings.)

  By this time I had asked my friends Timothy Ferris and Ann Druyan to help with the record project. Both had strong musical backgrounds and were enthusiastic about the idea of sending music to the stars. Ferris took charge of many of the production aspects of the project, particularly on the musical end, and Druyan provided vital contributions to all nonpictorial aspects of the record contents. Fortunately, John Casani of the Jet Propulsion Laboratory, NASA, had provided me with some money which permitted the project to partly reimburse these talented people for their time. With these funds I was also able to bring Jon Lomberg into the project. These individuals contributed a great deal of time for which they did not charge the project; and, with a few minor exceptions, all others contributed their time and talent gratis. I detailed Lomberg to work closely with Frank Drake in the selection and design of the pictorial portion of the message. Druyan organized an audio essay, “The Sounds of Earth,” an evolutionary sequence on the development of our planet, life, human beings, and the technical civilization responsible for the Voyager mission.