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A Scientist's Notebook
by Gregory Benford

A Portrait of Humanity

The Voyager spacecraft launched in 1997 recently slipped into interplanetary space beyond Pluto bearing a large phonograph record with images and sounds of Earth: a portrait of humanity.

This is the third column dealing with how a team of artist Jon Lomberg and astronomer Carolyn Porco and I designed a message to fly on NASA's Cassini spacecraft, launched in November 1997, bound for Saturn. We wanted to leave a message which would convey something of the people who sent the Cassini probe, and why.

Deep space is the best place to leave a long term message. Probably any message we make will not to be read by distant generations, but solely by the generation that launched it. To many, its true purpose is to appeal to and expand the human spirit, now.

Unlike listening for radio signals from extraterrestrials, sending messages inscribed on hard objects to distant worlds implies a vast time scale before any reward. Further, such acts demand that we explore what we should say, not how to fathom what others say.

We wished to send something similar to the Voyager spacecraft plaques, yet on a tiny surface, inscribing a photograph into the diamond wafer the size of a coin. Discussions ranged over many choices; I shall try to convey the flavor, often quoting or paraphrasing.

Based on the Pioneer and Voyager experience, Lomberg drew up a list of requirements that would both deflect the sort of criticism Pioneer's sketch of humans aroused, and minimize confusions among the eventual readers: "The photo must work in black and white and at low-resolution, showing a representative sample of humans with regard to age, sex, coloring, ethnic type, body type, dress and hairstyle." This last was to show that hair was natural and variable, yet was not clothing, which would also be deliberately diverse.

Further, the photograph "should show the entire human body, from head to toe, in several different positions" to give an idea of the range of movement. With "a minimum of overlap of detail in the poses, i.e., people not partially obscured by others," all objects would clearly stand out from background, and all individuals have equal visual importance. There would be social implications read into the photo by us and by any future readers, but at least we tried to not send signals we did not intend.

All felt that the picture must represent the planet without being too specific, certainly not a unique site or climate. The background should be information-dense, rich with details about the planet, species, and culture, though without compromising any of the above goals. Among this minutiae should stand out an object identical to something on the spacecraft to provide an unambiguous check of scale.

To stand for all humanity, we felt the photo should be open to humanity's inspection. Early on we agreed that the image should be broadly available. Still, to keep the picture from inappropriate uses, it was copyrighted.

Most of all, the photograph should convey beauty and wonder to our human eyes. We wanted no clinical examination of the human body, but an evocation of ourselves immersed in our world--and Cassini, an expression coming out of that passion.

Since we had discussed these ideas while walking in my home town, Laguna Beach, we immediately thought of an ocean setting. Lomberg lives on the big island of Hawaii, where isolated sandy beaches boast steady conditions for photography. With submerged lava rocks and waves rolling in, clouds in the sky, flapping birds and possibly a waning gibbous moon, we could convey much to a single glance from alien eyes. The beach should not be well known or easily identified; we wanted a generic beach that could be found on most continents or islands of Earth. Beaches have strong mythic and biological associations that enhance their relevance.

The photographer Lomberg knew best and wanted to work with was Simon Bell of Toronto. Bell is one of the world's best stereo photographers and kept the team from error many times. For his convenience, Lomberg and Porco considered a lake beach shot on the sandy shores of Lake Ontario. In the end this idea lost out. A lake does not impart the same feel as the ocean; waves are smaller and typically the coast is less varied.

Some facets we sought to convey more subtly: "the use and role of boats; the importance of water; the nurturing of children; information about the water-cycle and thus the approximate temperature." Cast shadows might imply the latitude or time of day, but for distant eyes that would be difficult.

We see the world in stereo, and a direct way to convey this would be to etch two stereo views of the same scene. This would also strongly hint that the curious bipeds in the photo saw with the odd symmetric spots on their upper heads. The disk's size serves to fix uniquely the distance between the "eyes" of the stereo views, so that images at all distances align properly. The camera separation for the shots was close to our own eye separation, again suggesting that's what our eyes are for.

The one object from the spacecraft we knew future viewers would have was, of course, the disk. One of the photographed adults should then hold the diamond disk, very clearly outlined against a background. To help alien perceptions, all or most of the people should be looking at it.

Porco reminded us of the Pioneer drawing, which to some implied a man was larger and thus more important than a woman. Never mind that the Pioneer team carefully used figures with the average height of men and women worldwide, they drew objections. Porco insisted that we should make a woman the focal point of the photograph, and Lomberg agreed. When finished, the photo provoked one woman to comment, "It'll tell them in the far future that Earth is a matriarchy. I love it!"

In the photo the central, seated woman holds the disk (actually, we didn't risk using the diamond, so substituted a plexiglass stand-in with the same optical reflecting characteristics). Others look at it. Its diameter sets the scale of the people and plants within view.

We agreed that while the adults and older child should be clothed, to avoid the Pioneer criticism, the younger children might be nude, to hint at how we reproduce. Casual, loose, and solid- colored, clothing should be shot to make it as easy as possible to see that it is a covering, and not a growth of the body. Women should be wearing little make-up, if any. Some small jewelry like rings or bracelets might be all right, if it were obviously artificial. No cross or other religious symbols, though; no favoritism should be implied.

Some people we spoke with thought it dubious to not show all people nude, for clarity. But many would object to or be embarrassed by pictures of naked adults. Lomberg carried the day by saying firmly, "If we want this photo to truly be representative of all the Earth, it is no small matter to alienate a large portion of the Earthly audience."

Also, Lomberg noted, people hardly ever walk around naked. In most cultures there is some sort of dress, a fundamental social fact about us. Shadows on the ground and a sun hat could give the very important information that we cover ourselves for protection from the environment. Astute observers might even draw some conclusions about avoiding too much solar ultraviolet at the beach.

As well, sexual differentiation will be guessable purely by obvious body shape differences and the breasts of the women. (But would non-mammals guess their use?) If these hints proved insufficient, the genitals would not provide strong clues as to their function. Necessarily there would be unseen parts of the body- -soles of the feet, inside of the mouth--so we could not be utterly clinically representative.

After all, the picture was not aiming to explain human biology or reproduction fully, but to satisfy the simple question: What did the creators of this message look like? The background could explain larger aspects. A shot angled along the beach would show incoming wave trains clearly. Ironwood conifers along the shore would include another great kingdom of life; the bacteria we would have to do without.

A collection of several different boats—wooden canoe, modern sailboat, fishing boat with motor-- might suggest our range of technology and our interest in traveling and vehicles, of which Cassini is one of the ultimate expressions. But more than one would clutter the composition, too. Sail size and mast height the viewers could use to roughly estimate our wind speeds and atmospheric density.

Birds in the sky would ring in another animal life form, but how could we count on them? A trained parrot balanced on a limb? This proved difficult to bring about during the long, grueling photo sessions. And a sitting bird would not imply flight. Luck would have to give us that, then, from the myriad shots necessary to get just the right one.

The time of day was another variable, but we could not see how to use it to carry much information. The sun's angle should be low enough to cast clear shadows but not so low as to cause problems with exposure times. The fidelity of the process which would inscribe the photo also set limits. In low-resolution black and white with little dynamic range, our main goal was clarity and clear outlines of objects, though stereo images and foregrounding important objects would help in sorting it all out, we hoped.

Naturally, we thought of the most dramatic possible shot, a sunset over the ocean. But Simon Bell shook his head. "Using flash may not work. Because I use two cameras, I have to slow the shutter speed to ensure that the flash is caught by both cameras. This would then affect the look off the waves, which we'd ideally want to freeze with a fast shutter speed."

Sunset also drastically reduces potential shooting times and locations and might compromise esthetics, since a good sunset looks best when the sky and foreground are underexposed, while skin tones look best when normally exposed. Using too much fill light to compensate could look artificial, too.

Myriad such considerations entered in the final, four-day long photo session, at two different beaches. The logistics proved almost military in scope, down to camping gear, food supplies, and a portable toilet. Lomberg organized all this, selected the sites and found the multi-racial models, all residents of Kona. Simon Bell flew in from Toronto, after trying model poses in his studio, and shot over 1200 slides.

Some had full frontal nudity, others were unclothed but more discreet. Some were fully clothed, as a hedge against NASA's suddenly balking at the last minute. Porco took the final candidate slides to Washington and showed them to NASA Administrator Dan Goldin, who approved the final selection. As luck would have it, the best shots had no birds flapping in the deep blue sky.

Now came time to assemble all this into a final design.

We planned to inscribe the reverse of the diamond with a straight line across the diameter, broken in the middle to show a "1u" symbol. The "u" stood for "unit" and was repeated elsewhere to show we were thinking of lengths.

Given sufficient dynamic range, the refractive characteristics of the diamond might be measurable in the photo. This might be used by readers to reconstruct some of the color. Bell doubted that our 64 gray levels would be up to this, though.

Above the "1u" line we depicted the first ten digits in binary code, then used binary everywhere else. In a sense the reverse side sets the terms of discussion: the photo says "Here is who we are." while the units tell them how we shall describe our world on the front side. Only the names of supporting laboratories and organizations at the very bottom carries any Kilroy aspect.

From top to bottom the scale goes from large to smaller. This echoes the view across a plane, with the bigger scale of the horizon higher in the field of view. So also on the front side, with the Big Dipper, M71 and the Hercules cluster at the bottom and the Earth at the top.

Above the stellar pictures is an accurate, scaled map of the solar system, showing planets, symbols for them, and the Cassini- Huygens trajectory through them, establishing our home. Above this is a gallery of previous space craft such as Viking, Pioneer, and Voyager. (This actually violated the larger-to-smaller scheme, alas, but seemed necessary to tie the idea of such vessels to the planets they explored, shown in a matching gallery of planet photos directly above each spacecraft. Only Earth has no craft, suggesting that we live there.)

Above this gallery is a highly detailed Saturn with its planetary symbol. An accurate trajectory marks the Cassini orbiter separation from the Huygens probe. To the left is a six-axis view of the Orbiter, to the right of Huygens. Above this row are Earth photographs, four of ninety-degree rotations and two of the poles. Tom Van Sandt of the Geosphere Corporation generously gave us cloud- free, consistent lighting maps. From these we hoped continental drift dating could be done.

Many compromises lie behind these views. Could eyes in the far future translate the slanted perspective of the solar system diagram into a three-dimensional reality? We could but hope.

These were the plans as of January, 1997. Throughout 1994-7 the issue of how to write on diamond was a continuing technical puzzle. The final method adopted was etching by an oxygen and sand plasma. Oxygen etches all carbon-based materials, but optimizing this process demands much experience.

My doctorate was in solid state physics, so I was the natural person to deal with such issues. Quickly I learned how little I knew of technological advances in the last two decades; I was woefully out of date. We swiftly fell back on real experts, and got excellent technical support from many.

Public exposure had already begun well before this work. One day in early February, 1995, my telephone rang, announcing a leak. The British popular magazine New Scientist wanted to run a piece on the plans. Apparently they had sniffed out rumors from the European Space Agency. I guardedly confirmed what they already knew and corrected some errors. Immediately after hanging up I e-mailed Porco, Lomberg, and JPL. Porco seemed panicked, but I saw little harm. After all, the local newspaper (the Orange County Register) had also carried an extensive piece later in February 1995, based upon a reporter sitting in on our discussions at UCI. It provoked no follow-up journalism, and neither did the New Scientist piece.

Porco asked me to write New Scientist to correct their omission of her name, a request which seemed at odds with her anxieties about keeping a low profile. Still, I thought little of it. New Scientist published my letter, and a further note from Porco as well, establishing credit.

Coincidentally, a paper I had co-authored on wormholes was getting enormous press coverage, appearing in over a hundred newspapers; it was a wild idea and counted among its authors sf writers Robert Forward, Geoff Landis and John Cramer. The diamond marker drew surprisingly little interest. Wild ideas play well in the press, but we expected as launch date approached the disk would get some mention.

Porco was much exercised about the New Scientist story. I reasoned that perhaps she was echoing NASA's extreme concern that nothing about a marker be made public before it was a done deal. The Pioneer plaque had provoked criticism, ranging from those perturbed by depicting nude humans to feminists who disliked its showing a woman shorter than a man, and in a different posture (less upright). In retrospect, the photograph eventually shot to go on the marker inevitably would have piqued some, since it showed a rather politically correct grouping of all races, with a woman as the centerpiece.

Porco and Lomberg worked through the principal remaining tasks: sharpening the concepts, detailed drawing of the disk etch pattern, and walking the diamond disks through the etching process. These first two fell to Lomberg, consuming many months of tedious labor. Porco handled most of the etching.

Meanwhile, NASA was pondering our efforts. As with Voyager, our design team operated on its own, with minimal engagement of the busy engineers. However, Charles Kohlhase, Manager for Science and Mission Design of the Cassini Program at JPL, decided that any marker or disk should carry no commercial insignia and issued a general directive stating so.

At about this time we heard that the JPL Cassini group had begun to create their own marker. Previous missions all the way back to the Mars Viking lander, and perhaps even earlier, had carried the names of principal engineers, etched onto metal strips. Why not expand this idea and include the public?

With little time to spare, this Kilroy Was Here gesture could attract attention, public involvement, more hits at the Cassini web site. The Planetary Society joined in. Anyone who wanted their name to fly to Saturn had only to mail in a signed postcard. Signatures were cut out and scanned by the Planetary Society, then digitized and loaded onto a compact disk. After a national campaign roping in congressmen and canvassers, the grand result was 616,403 signatures on the carrier—named, in high bureaucratic style-deaf fashion, the Digitized Versatile Disk.

My congressman, Christopher Cox, sent all his constituents a letter promising to funnel their names through his office and onto the Cassini spacecraft: "Your name will live on in space long after your grandchildren, and theirs, and theirs." They obtained some celebrity signatures from Star Trek actors and congressmen, baby footprints, and pet paw prints.

The European collaborators got wind of all this and started their own signature collection. They took the signature disk a step further and planned to sell a duplicate disk after the launch, reasoning that people who were to be immortalized on the interplanetary scale would, of course, want a copy. Like JPL, they set up a world wide web site to send names and messages. They got such memorable phrases as "Hello green worms," "HELP" and "Don't cry because you cannot see the sun, because the tears will stop you seeing the stars."

The Europeans never managed to get their hundred thousand signatures transmitted to JPL in time, so those are not on the Orbiter. Therefore the European Space Agency attached their own disk to the Huygens lander, while JPL's names fly on the Orbiter. The JPL team was uneasy about lack of screening of the ESA names and the European's plans to sell their disk commercially.

All this activity to collect a meaningless string of names and salutations emulates the portion of the Voyager record of least value, the list of Congressional committee members that NASA forced the Voyager team to include.

Cassini's compact disk surely will not survive for more than a century or so, nor could it be easily read in any distant future. Even very clever humans or aliens could not figure out the encoding software from first principles, and should they, they would get only a list of indecipherable, disorganized names, and a few cryptic, disconnected messages in this sea of words.

One could imagine a far future discoverer wondering what to think of a species that created a message without attempting to make it "comprehensible, self-extracting, anti-coded, triply redundant, and graduated in content," as Lomberg summed up the Voyager and diamond disk approach. As a projection of pure vanity it resembles the International Star Registry, which sells people certificates stating that stars have been named for them. Such meaningless exercises in ego tell more about our species than we might like revealed.

This Kilroy disk emerged only after the diamond marker idea became known. It had every sign of a hastily designed public relations stunt. Including long lists of names is a cliche of time capsules. Apparently the largest collection was the 22 million assembled and buried at the order of President Ford for the bicentennial celebration in 1976.

As Kohlhase put it to me, knowing that I looked askance at the signature disk, he and others devoted eighteen months of hard work to produce a "heart-based signature disk," in contrast to the "mind- based diamond."

Of course, both gestures spring from a common impulse: to give people a sense of connection with something larger than themselves. To value this is to rank the expressive quality of deep time messages over their communicating ability.

My trouble with all such name-gathering was that the end result more nearly resembled the graffiti which disfigure many ancient monuments. After all, the scribblers upon the Parthenon no doubt felt some burst of elation, too, but the end result besmirched the work which is the point of it all.

Lomberg regretted that the signature disk would get commingled in the public mind with the actual message marker, vastly increasing the ratio of noise to signal, as engineers put it. Indeed, the Planetary Society has now made this a feature of their membership drives; in 1997 they attached a microchip to the Stardust mission to rendezvous with a comet. "And you'll be a part of it all," an advertisement promised.

We can expect that such masses of names will become a standard fixture of a publicity-conscious space program. Indeed, shouting at the stars will become a commonplace. In 1998 the Sci-Fi Channel tried to arrange transmission of signature messages by radio beamed skyward. An entrepreneur tried to sell space on metal plates to be launched to the stars. None seems to have even thought about how utterly distinct life forms could say something understandable to each other.

So matters rushed on, as the launch deadline neared: October, 1997. Cassini did lift off in November after several delays. In those last months much more happened, as I shall treat in a forthcoming book, Deep Time. The saga of sending messages into the high vault of vacuum is a continuing tale of human frailty and ego.

But it means something that we modern humans try. Our signals across the stretching spans of centuries may convey little, but they do mean this: something deeply human wishes to connect with those who come after us. We yearn, across both space and time, for the eternal.

Comments and objections to this column are welcome. Please send them to Gregory Benford, Physics Department, Univ. Calif., Irvine, CA 92717. email:

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