Category Dreams of Other Worlds

We inhabit a physical universe filled with electromagnetic radia­tion spanning a factor of trillions in wavelength. The human eye sees only a sliver of this radiation, designated as visible light. It’s as if there was a full piano keyboard in front of us with eighty-eight keys and we were restricted to making music with two adjacent keys or notes. Space telescopes like Spitzer and the Chandra X – ray Observatory, covered in the next chapter, have opened up the palette of sensation and given us an octave or more with which to view the universe. Infrared astronomy, in particular, has been instrumental in revealing how stars and their planetary systems form. Spitzer can see through the vast clouds of dust, within which myriad stars are being born, and can penetrate the granular torus or dense disk that typically surround newborn stars. This capabil­ity has literally opened people’s eyes to the worlds that lie beyond the red end of the rainbow.

Isaac Newton first identified the colors of the visible spectrum by observing sunlight passed through a glass prism. William Her – schel later investigated temperatures associated with each color of visible light. Having in 1781 discovered Uranus, the first new planet since antiquity, Herschel was already the greatest astrono­mer of his age when he began experimenting with light. He noticed that heat passed through various colored filters used to observe the Sun and carried out experiments to understand this phenomenon. Using a thermometer with a soot-blackened bulb to better absorb heat, Herschel measured the temperature of each color band of vis­ible light and noticed that the temperature increased from the vio­let to the red end of the visible spectrum.6 Surprised to record the highest temperatures beyond the edge of the red band, Herschel realized that electromagnetic radiation existed in wavelengths we can’t see. He had detected infrared light. Such early discoveries regarding the electromagnetic spectrum paved the way for remark­able new possibilities in studying the universe.

Light is conventionally subdivided by wavelength into radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray, with radio designating cool, long wavelengths and gamma rays representing the highest energy, short wavelengths. These subdi­visions are merely convenient demarcations for differences along a continuum of electromagnetic radiation. While most forms of radiation can’t reach the ground from sources in space (figure 9.1), all forms of electromagnetic radiation, from radio to gamma rays, travel at the same speed as light in a vacuum, approximately 300,000 kilometers per second or 186,000 miles per second. We’re intimately familiar with most of these bands of radiation. Radio waves transmit music and news on your favorite radio station. Microwaves make possible communication technologies including cell phones and, of course, in microwave ovens. Ultraviolet radia­tion can quickly give you a suntan or sunburn and is the means by

which our bodies produce Vitamin D. We became familiar with UV light from the 1970s black lights. X-rays have been invaluable in medical and dental practice as well as in fluoroscopy, which offers real-time views through living tissue, while high-energy lasers are used in brain and eye surgery and other delicate medical proce­dures. Radiation at infrared wavelengths also has powerful thera­peutic effects. Low-level, “cold laser” therapy contributes to the healing of wounds as noted in a report cited by the National Cen­ter for Biotechnology Information.7 A near infrared light-emitting diode developed by NASA has been used to heal and reduce pain for chemotherapy patients who subsequently suffer from mouth lesions.8 In the past fifty years, we’ve harnessed this invisible radia­tion to vastly improve our lives.

Spirit and Opportunity are squat and sturdy, as large as golf carts and almost as tall as an adult (plate 3). Each weighs 400 pounds.18 They have six wheels, each with its own, independent motor. Four – wheel steering allows them to make tight turns and swerve or turn on a dime. The design is based on the “rocker-bogie” system of the previous Sojourner rover.19 The wheels can swivel in pairs and pivot vertically to maintain overall balance. The saddest thing that could happen to a very expensive rover millions of miles from home would be for it to tip over onto its side or back, wheels spin­ning uselessly. So Spirit and Opportunity have a suspension system that balances the load any time a wheel goes up or down. As a result, the bodies of the rovers experience half the range of motion of the wheels and legs. The rovers can tilt up to 45 degrees without overturning, but software is designed to sound the alarm any time the tilt exceeds 30 degrees. The wheels have cleats for gripping in soft sand and scrambling over rocks.

In case you had a mental image of a NASA engineer, cap turned sideways, slamming a joystick from left to right as the rover ca­reens over the Martian dunes, the truth is a bit more sedate. The rovers have a top speed over smooth ground of 2 inches per sec­ond, or 1/10 of a mile per hour. But even at that speed, there’s no danger of recklessness; hazard avoidance software is used that makes each rover stop and evaluate its progress every couple of seconds, reducing the true speed to a glacial 1/50 mph. On Earth, the rover might get overtaken by a snail.

The body of the rovers is the warm electronics box, a tough outer layer designed to protect the computer, electronics, and batteries—the rover’s brains and heart. These vital organs must be buffered from the worst extremes of the Martian climate. Tem­peratures at the landing sites can plunge from a daytime high of 70°F to a nighttime low of -150°F, a range many times larger than we’re accustomed to on Earth. Engineers use gold paint, heaters, and insulating aerogel to keep the rovers in a comfort zone. Within the warm electronic box, the “brain” of each rover is a computer that receives data from the scientific instruments and relays it to one of the Mars orbiters and then on to Earth. Spirit and Oppor­tunity are exquisite machines, but they’re far from state of the art in terms of processing power and data transmission rate. Moore’s law—the near doubling of computational power every eighteen months—marches on, but the hardware on the rovers had to be tested for the severe conditions of space and “frozen” long before launch. So each rover’s brain has only 128 Mb of RAM, and the data rate to the orbiters is 128 kb per second. That’s the equiva­lent of a very low-end netbook and only twice as fast as a dial-up modem. If you have an iPhone, it easily eclipses the computational capabilities of both rovers.

The beating heart of the rovers is their solar panels. Mars re­ceives half the intensity of sunlight that the Earth does, and it’s a real challenge to gather enough energy to power the rover and its suit of instruments. Each rover can function on 140 Watts, the equivalent of a standard light bulb. The deck of each rover is tiled with solar panels which charge batteries within the warm electronic box. As the Martian winter approaches, there’s insuf­ficient power for driving, so each rover navigates to a north-facing slope and hunkers down for the months in which the tempera­ture remains below freezing. This imperative has always been greater for Spirit, which is much farther from the equator than Opportunity.

Of the stunning images Voyager sent back, perhaps none have more profoundly shaped our understanding of humankind’s place in space than Voyager 1’s photo of Earth from the icy reaches of the outer Solar System. The “Pale Blue Dot” image represents one of the most significant of the mission and of our time. In Febru­ary 1990, while 3.7 billion miles from Earth, Voyager 1 snapped sixty photographs looking toward the Sun, and over the next three months transmitted the images to Earth. Among the last six frames of the photo shoot, only one included humankind’s most distant view of Earth. When Sagan suggested that Voyager’s imaging team attempt the photographs, NASA administrators apparently were reluctant to authorize it, as programming the commands to take additional images was labor intensive and it was not clear whether the data would be scientifically useful. Candice Hansen, who helped design Voyager’s imaging observations, and several oth­ers joined Sagan in arguing for the photographs. Hansen recalls how intently the imaging science team wanted to obtain what was later called the Family Portrait: “We were really after the picture of the Earth, so we had to look for the point in the Earth’s orbit which would have it as far away as possible from the Sun. It turned out that we could also get Neptune, Uranus, Saturn, Jupiter, and Venus.” Hansen, like Sagan, realized that an image of Earth viewed from billions of miles away would intrinsically “strike a chord. . . that might affect people’s view of the world.”30 They couldn’t have been more prescient.

By sheer chance, the Earth appears in the photo as though caught in the band of a rainbow. This artifact in the image is caused by sunlight reflecting off the spacecraft (figure 4.3). Sagan noted that it only accentuated how diminutive our world is in the empty wastes of outer space. Jurrie Van Der Woude, public infor-

mation officer for the mission, explained the difficulties in actually acquiring Voyager’s final six photographs, including the singular image of Earth that so powerfully and visually characterized our minute place in space:

They were stored onboard Voyager on the tape recorder, for the simple reason that the Deep Space Network—those big antennas in Australia, Madrid, and Goldstone, California—were too busy with Ma­gellan and Galileo to listen to poor old Voyager. At the end of March, we played that sequence of photographs back, and the last series of photographs, five or six, were being received by the Madrid antenna when it rained. That blocked out the data, so in April we had to give it another shot. This time the antenna in use was the one at Goldstone, which turned out to have a hardware problem. As a result we still did not get those six photographs, so we had to do it again in May, when we finally got them.31

Wyn Wachhorst writes, “To stand on the moons of Saturn and see the Earth in perspective is to act out the unique identity of our species.”32 Wachhorst quite accurately points out that viewing Earth from the outer planets had radically altered our collective human consciousness. The Apollo missions afforded us the first opportunity to see the Earth from 240 million miles away. Apollo 8’s photo of the gibbous Earth emerging from the limb of our desic­cated and cratered Moon, Earthrise, along with Apollo 17’s Whole Earth photo are among the defining images of the manned lunar program and of the twentieth century. Apollo 8 astronaut James Lovell, commenting on the view of Earth as the astronauts orbited the Moon in December 1968, noted: “The [E]arth from here is a grand oasis in the big vastness of space.”33 Voyager, conversely, had captured a chance glimpse of the dot of Earth forging into the empty abyss on its course around the Sun. In 4.5 billion years, our Solar System has never traversed the same wastes of space—nor will it ever. It is a staggering reorientation made visceral through the photo of the pale blue dot. With that single image, Voyager brought into focus the fractional blue world on which our lives, our narratives, and our art have mattered.

In Alien Ocean: Anthropological Voyages in Microbial Seas, Stefan Helmreich argues that the discovery of life deep in Earth’s oceans provoked increased speculation about the possibility of life in ex­traterrestrial seas. Prolific communities of tubeworms, krill, and other hypothermophiles were discovered near deep-sea hydrother­mal vents in 1977 in the Pacific Ocean.43 These organisms live in complete darkness—no sunlight can penetrate to these depths. Sci­entists speculate whether life in primordial times thrived in the sulfur-rich heat plumes that spew nutrients from the ocean floor. Besides the fact that we believe all life on Earth originated in the sea, we have long imagined, notes Helmreich, that extant primeval life-forms might somehow survive in the deep, even today. Life’s origins may best be represented by extremophiles currently living in extreme environments. He writes, “Some marine microbiolo­gists maintain that vent hyperthermophiles are the most conserved life forms on the planet, direct lines back to the origin of life.”44 What we are learning about extremophiles or methanotrophes— bacteria that metabolize methane—may indicate something of the possibilities for life on other worlds. “Astrobiologists treat unusual environments on Earth, such as methane seeps and hydrothermal vents, as models for extraterrestrial ecologies,” writes Helmreich.45 Cassini has revealed that several of Saturn’s moons have liquid or frozen oceans and briny geysers. Enceladus, with its outgassing plumes of ice water and salt, and Titan, are of particular inter – est.46 As the planetary body in the Solar System most similar to

Earth in atmospheric composition, Titan could reveal how life on Earth emerged, suggests astrobiologist Chris McKay.47 Since Titan and Enceladus are likely heated internally by Saturn’s gravitational squeezing, astrobiologists imagine that extremophiles might hud­dle near hydrothermal vents on the floors of their arctic seas. On Earth, Lake Vida in the Antarctic has been capped under a 50-foot thick ice sheet for 2,800 years and yet researchers found ancient microbial life thriving there.48 Helmreich comments, “For astro – biologists, life, extremophilic or no, will exist in a liquid medium. It is for this reason that extraterrestrial seas—alien oceans—are such objects of fascination.”49 In these discoveries alone, the im­plications of the Cassini mission are as deeply cultural as they are scientific.

It’s a space scientist or engineer’s worst nightmare. Your mission is working flawlessly and then, due to oversight or unforeseen events, its starts tumbling out of control. Several hundred million dollars’ worth of hardware turns a blind eye to its scientific mission. Deaf to telemetry and far beyond the reach of astronauts, it languishes uselessly in deep space.

On a June evening in 1998, mission controllers at NASA God­dard Space Center in Maryland took note as SOHO put itself into Emergency Sun Reacquisition mode. This mode is a safe “holding pattern” autonomously entered by the spacecraft any time it en­counters anomalies. From this point, the ground controller sends a special sequence of commands to recover normal science opera­tion, the first step of which involves pointing the spacecraft at the Sun so it knows where it is. Since SOHO had entered this mode five times since its December 1995 launch, the controllers weren’t too worried. But this time was different. Over the next few hours, a series of mistakes seemed to doom the spacecraft, first causing loss of attitude control, followed by an interruption in crucial te­lemetry, then loss of power, and finally loss of all thermal control. It was a bleak day, and it appeared to be the death knell for the young mission. In the control room, the tension grew in waves.20 At the first entry into Emergency Sun Reacquisition (ESR) Mode, engineers calmly issued the commands to point SOHO at the Sun by carefully orchestrating its three roll gyroscopes. Project scientist Bernhard Fleck said there was no undue concern. Even when a sec­ond ESR was triggered a few hours later, there was no panic; engi­neers had seen this before too. But as the roll thrusters were firing to point SOHO at the Sun, a third ESR was encountered. Out in deep space, a million miles from Maryland, SOHO was spinning faster and faster. Then the communication link went down, pre­sumably disrupted by the spacecraft’s wild motion. SOHO was unreachable.

The subsequent investigation showed that the spacecraft per­formed as designed; all the errors were human. In hindsight, Fleck thinks they gained a false sense of security after two and a half years of operations.21 Like pilots who had done many takeoffs and landings and who had flown on sunny days and through thunder­storms, they thought they had seen it all. They didn’t realize they were in a nosedive.

With the spacecraft seemingly lost, NASA and ESA quickly con­vened a review board to issue a diagnosis and post mortem.22 The review board concluded that seat-of-t he-pants decision making in the control room exacerbated the problem. Controllers erro­neously removed the functionality of SOHO’s normal safe mode and misdiagnosed the state of two of the three gyros. At any time during the mishap, if they had verified that Gyro A was not con­trolling the roll angle properly, they could have avoided the serious problem. The mundane and somewhat sheepish conclusion: when a very complex system is made and operated by human beings, sooner or later they’re going to do something wrong.

Ground controllers kept trying to send messages to SOHO using the Deep Space Network, but they had heavy hearts. The spacecraft was in an uncontrolled spin, possibly at a rate that could cause structural damage. Engineers believed it was spinning with its solar panels edge-on to the Sun and so not generating any power. As a result, the batteries and the onboard fuel would have frozen into a state from which they could not be recovered. But there was a window of opportunity that admitted a sliver of hope. SOHO’s steadily changing orbit with respect to the Sun was increasing the illumination on the solar panels for a few months and they would give the batteries a chance to recharge. Twelve hours a day, controllers “pinged” SOHO in the hopes of getting a response. Then, a month after contact with the spacecraft had been lost, a break. The huge 305-meter radio dish at Arecibo was able to bounce radar off SOHO and the refection was picked up by the Deep Space Network dish at Goldstone. SOHO was spinning at a modest rate of one revolution per minute. Communicating with the frozen spacecraft was not easy, but six weeks after contact had been lost a feeble signal was received. SOHO was alive.

Over the next two months, engineers clawed SOHO back from the brink. They thawed out its batteries and fuel lines and were gratified that none of the scientific instruments seemed worse for wear after having been subjected to temperature variations from +100°C to -120°C. Some of the instruments even improved their performance after experiencing this bracing range of temperatures. SOHO was back, but two of the three gyros were not respon­sive due to the series of mishaps. As luck would have it, the third gyro failed a few months later. Although the gyroscopes were not needed to gather science data, maintaining a Sun-oriented attitude used valuable fuel and lowered the margins of safety if anything else should go wrong. Undaunted, the engineers made lemonade with their lemons. They developed special software to enable the spacecraft to point using the control reaction wheels, the first time an ESA spacecraft had ever been operated without gyroscopes. For all the detailed planning, SOHO ended up living by its wits in a series of knife-edge decisions.

The Earth and its atmosphere emit infrared radiation in all direc – tions,9 swamping any signals from space. It’s analogous to trying to see stars in the noontime sky. For a faint, cool source to stand
out against a warmer backdrop, an infrared telescope must lower thermal backgrounds. Which is to say, the longer the wavelength of light being observed, the colder a telescope and its detector need to be to see an infrared source from space. By the 1960s, infrared astronomy took off with the development of a new type of solid-state detector that had greater sensitivity than old-style radiometers.10 Another obstacle to detecting infrared radiation from cosmic sources is the fact that those waves are absorbed by water vapor in the air we breathe. Astronomers initially chose high mountaintops for their observations, to be above as much of the infrared-absorbing atmosphere as possible. For example, some of the best infrared observations are made 4,200 meters high atop the dormant volcano Mauna Kea in Hawaii, and new telescopes are being constructed in the arid Atacama Desert in Chile, includ­ing a major new millimeter array on the Chajnantor plateau at an altitude of 5,000 meters. An extreme version of this strategy was the Kuiper Airborne Observatory, which operated from 1974 to 1995. This 36-inch telescope in a converted Air Force C141 jet made observations for a few hours at a time at an altitude of 45,000 feet. The successor to this facility is a 2.5-meter telescope in a converted Boeing 747-SP, the Stratospheric Observatory for Infrared Astronomy.11 High-altitude balloons and rockets carrying small telescopes have been used to reach even higher altitudes of over 100,000 feet.

It proved essential to cool infrared telescope detectors to liquid nitrogen or even liquid helium temperatures so that radiation from the detector wouldn’t wash out signals from the sky. On ground – based telescopes observing the near infrared, two to six times the wavelength of visible light, liquid nitrogen is used to cool the de­tector to 77 Kelvin or -177°C. Though seemingly exotic, liquid nitrogen is basically liquefied air and costs no more than milk. For observing at the mid-infrared, 20-200 times the wavelength of visible light, liquid helium is used to cool the detector to 4.2 Kelvin or -269°C, a hair’s breadth from absolute cold. But the Earth environment emits so much radiation at these wavelengths that astronomical signals are swamped by background radiation and deep mid-infrared observations can only be made from space.

Space infrared astronomy was kicked into gear with the very successful NASA Infrared Astronomical Satellite (IRAS) mission,

which in 1983 surveyed the entire sky in the infrared for the first time. In less than a year, IRAS detected about 350,000 infrared sources. Around the same time, ESA launched the Infrared Space Observatory, which had higher sensitivity and much broader wave­length coverage.12 In 1997, an infrared camera was added to the instrument suite of the Hubble Space Telescope. This camera has been very successful but it has a small field of view and shares time with four other instruments, so infrared astronomers had always planned for their own facility.

Spitzer, from its earliest inception, was especially designed for infrared astronomy and is sensitive enough to detect infrared sig­natures of stars and galaxies billions of light-years away. The space telescope has been instrumental in unveiling small, dim objects like dwarf stars and exoplanets and can even determine the tem­perature of their slender atmospheres. Originally proposed in the late 1970s as NASA’s Space Infrared Telescope Facility, the Spitzer Space Telescope suffered from uncertainty, a delay after the loss of the space shuttle Challenger, near-cancellation, congressional limbo, budget cuts, and “descoping.” Nevertheless, in 2003 the telescope was finally launched, after being renamed subsequent to a public opinion poll conducted by NASA. The last of NASA’s four Great Observatories, the $800 million telescope was named after Lyman Spitzer, an early advocate of the importance of or­bital telescopes.13 After launch, the spacecraft took about 40 days to cool to its operating temperature of 5 Kelvin. Once cooled, it took just an ounce of liquid helium per day to maintain its detec­tors at their operating temperature. A solar panel facing the Sun serves to gather power and protect the telescope from radiation. On the anti-solar side, a series of concentric shells and a black shield radiate heat into space. Spitzer’s most precious resource was its liquid helium, used to cool the telescope and its instruments to the phenomenal temperature of just 1.2 Kelvin, within an iota of the temperature where atoms and molecules have no motion. This extra cold relative to the liquid helium operating temperature comes from venting the helium into the vacuum of space, much as your skin would cool if a liquid evaporated from it. Background radiation is reduced by a factor of a million relative to a similar­sized telescope on the Earth’s surface. The telescope’s cryostat held 350 liters at launch, as much as the gas tank of a large minivan. Helium evaporates and is boiled away by tiny heat inputs from the instruments and from the telescope structure, so the act of observ­ing steadily depletes the cryogen.

The goals of cooling the telescope and preserving the liquid he­lium as long as possible dictated the telescope’s orbit and design. Careful design minimized these heat inputs, which are typically measured in milliwatts. As a reference, your fingertip radiates 25 milliwatts. The Spitzer facility is 4.5 meters tall and 2.1 meters in diameter and weighs about as much as a minivan. Previous space observatories had used either a low Earth orbit to be serviceable by the Space Shuttle (such as the Hubble Space Telescope) or a high Earth orbit with a period of one to two days (like the Chan­dra X-Ray Observatory). Spitzer is in an unusual Earth-trailing solar orbit. The big benefit is in escaping from the Earth’s heat and being situated in a good thermal environment where the tele­scope can cool in the vacuum of space. The orbit also avoids the Earth’s radiation belts, and there’s excellent efficiency of observing because the Earth and Moon rarely intervene. But one disadvan­tage is that Spitzer’s radio signals are getting weaker as it moves away from Earth. Spitzer slips away from Earth at about 10 mil­lion miles per year and is now farther away than the Sun. Only the huge 70-meter dishes of the Deep Space Network are sensitive enough to gather its precious data. Mission planners estimate that they will lose touch with Spitzer in early 2014.

If you were a field geologist, your most valuable asset would be your eyes. Geologists are trained to recognize rocks and minerals and crystals, using archetypal images in textbooks and samples in the lab. But hand-picked samples, viewed in isolation, can never prepare a geologist for the complexity and apparent chaos of a real landscape (figure 3.1). Rocks are sometimes layered and sometimes jumbled, their color and texture can change according to lighting conditions and perspective, and each rock’s story only makes sense in the light of the surrounding terrain. Experienced geologists must take all this in through their eyes. With little atmosphere on Mars to carry sound or smell, sight is the critical sense.

The rovers’ eyes sit at the top of a mast, roughly five feet off the ground. Twin CCD cameras are used to form stereo images. The cameras can rotate 360 degrees to make a complete panorama, and pivot 18 degrees to scan the landscape or the sky. With 16 megapixels, they are similar to high-end digital cameras you could buy, and each one weighs nine ounces and could fit in the palm of your hand. But unlike a commercial device, the rover cameras have a large set of color filters designed to help diagnose the composi­tion of rocks and minerals, and a set of solar filters for looking at the Sun. Like some new cars, the rovers also have “hazard avoid­ance” cameras, one pair on the front and one pair on the back,

each looking ten feet out to help avoid any unexpected collisions or obstacles.

Spirit and Opportunity may be one-armed geologists, but those arms are highly capable, with an elbow, a wrist, and four modes of motion. In the mechanical “fist” of each arm is a pint-sized im­ager that acts like the hand-held magnifying lens carried by many geologists. Just as no geologists would do any fieldwork without their trusty hammer, so each rover arm is equipped with a Rock Abrasion Tool (or RAT). The RAT is a muscular, diamond-studded grinder; in two hours it can carve out a hole 2 inches across and 1/5 inch deep into even the hardest volcanic rock.20 Rock interiors can be quite different from the exteriors, which have been subject to weathering and radiation and may be coated in dust. After the RAT has finished its work, the microscopic imager can peer into the hole and two other science instruments can be pivoted into po­sition to study the rock. One, called a Mossbauer spectrometer, is specifically designed to study iron-bearing minerals with high pre­cision. It takes about twelve hours to do a single measurement. The other is called an Alpha Particle X-ray Spectrometer. It has an on­board source of alpha particles—high-energy helium nuclei—and it can bounce either those or X-rays off the rock sample. The re­sults give the elemental composition, which is important in decid­ing how different chemicals came together to form minerals within the rock. These measurements take about ten hours per sample.

The rovers’ suite of sophisticated instruments is completed by the Miniature Thermal Emission Spectrometer. All objects emit heat, and the spectrum of their heat can be used to deduce their composition. This instrument is particularly designed to look for minerals that can only be made in the presence of or by the action of water, such as carbonates and clays. It weighs five pounds and it sits in the rover’s body, but it has a periscope so it can look out alongside the rover’s eyes, and it can also gaze upward to gather measurements on the temperature, water vapor content, and pres­ence of dust in the atmosphere.

Finally, like many good science fair projects, the Mars Explora­tion Rovers make use of magnets.

Magnetic dust grains are freeze-dried remnants of the planet’s wetter past, where some types of molecules align with the Martian magnetic field when they are in solution, and then preserve that ori­entation when the mineral solidifies. Magnetic minerals give addi­tional clues to the geological history. One pair of magnets sits at the end of the robotic arms, where it can gather magnetized particles ground out by the RAT. Another pair of magnets is at the front of the rover, tilted such that non-magnetic particles will fall off. Two of the spectrometers then analyze any particles that stick there.

Attached to each Voyager spacecraft is a gold-plated, copper pho­nograph record conveying greetings from Earth to civilizations potentially inhabiting nearby exoplanets in our galaxy (plate 6). Though not the first spacecraft to carry salutations from Earth, Voyager is the first to send our voices, music, and photographs. Pioneer 10 and 11 carry a plaque that includes a map of nearby pulsars indicating the Sun’s location in the Milky Way, a schematic of our Solar System, their flight path from the third planet out, and an outline of the Pioneer spacecraft with the outlines of a man and woman standing in the foreground to demonstrate the humans’ shape and comparable size. The male figure has his right hand raised in a sign of greeting. By contrast, Voyager carries much more detailed salutations to potential species that might happen upon the spacecraft.

The idea of attaching greetings from Earth to the Voyager spacecraft apparently was suggested by John Casani, who served as project manager for Voyager from 1975 to 1977. In October 1974, Casani had scribbled on a routine JPL concern and action report: “No plan for sending a message to our extrasolar system neighbors,” as well as the phrase, “Send a message!”34 Casani asked Carl Sagan to coordinate putting together a message. Sagan was a natural choice to head the effort; he and Cornell astrono­mer Frank Drake had organized development of the Pioneer 10 and 11 plaques. Sagan understood the powerful public impact of a greeting to possible galactic civilizations, eagerly accepted Casani’s mandate, and recruited a group of scientists, profes­sors, and business leaders for the NASA Voyager Record Com – mittee.35 Sagan additionally consulted with science fiction writers Arthur C. Clarke, Robert Heinlein, and Isaac Asimov and gath­ered a core group of collaborators including Drake, who in 1961 developed an equation for calculating the number of civilizations that might populate the Milky Way, writer Ann Druyan, science writer and professor Timothy Ferris, astronomy-inspired art­ist Jon Lomberg, and artist Linda Salzman Sagan, who drew the images for the Pioneer plaque. This core group selected the mes­sages, sounds, music, photos, and diagrams now hurtling into the interstellar abyss.

Inscribed in the grooves of the Golden Record is an essay of sounds of Earth; spoken and written greetings; humpback whale song; 115 photographs and diagrams related to nature, science, and human activities; and ninety minutes of music. Murmurs of Earth, an account of the compilation of the interstellar record, reveals the intense deliberation that went into selecting its con­tents and determining the medium that would best preserve this special envoy from Earth. It was Drake who recommended using the equivalent of a phonograph record that could record sound as well as photographs that would render as television images. Since corrosion does not occur in the vacuum of space, it was calcu­lated that, excepting a direct collision with micrometeoroids or other space debris in our Solar System, the records might remain intact for a billion years. “We felt like we were on the commit­tee for Noah’s Ark, that we were deciding which pieces of music and which sounds of Earth would be given eternal life, really a thousand million years. We took it as a kind of sacred and joyful task,” recalls Druyan, who gathered the audio clips for the record’s twelve-minute sound essay.36

The sound essay begins with a musical rendering of Kepler’s Harmonica Mundi, a mathematical treatise transposed into sound at Bell Telephone Laboratories. “Each frequency represents a planet; the highest pitch represents the motion of Mercury around the Sun as seen from Earth; the lowest frequency represents Ju­piter’s orbital motion. . . . The particular segment that appears on the record corresponds to very roughly a century of planetary motion,” explains Druyan. Following this are sounds of the pri­mordial Earth: volcanoes, earthquakes, thunder, and mud pots. To illustrate the evolution of life, ocean surf, rain, and wind are fol­lowed by crickets and frogs, then vocalizations by birds, hyena and elephants, and a chimpanzee. Human footsteps, heartbeats, speech, and laughter come next and fade to the sound of fire and of flint being struck by rock to indicate the evolution of tool use. These are followed by a tame dog’s bark, and the clamor produced by sheep herding, blacksmithing, sawing, and agriculture. Next is Morse code tapping out the phrase Ad astra per aspera, which translates as “to the stars through difficulties,” a suggestion by Carl Sagan. To trace the evolution of travel technologies in the twenti­eth century, the clatter of horse-cart and noise of an automobile segue to an F-111 flyby and the cacophony of a Saturn V liftoff. Concluding the sound-essay are juxtaposed sound files of electro­magnetic waves of human brain activity, actually those of Druyan, in case an advanced civilization could read human thoughts, and the radio output of a pulsar, a collapsed star in rapid rotation. As Druyan points out: “My recorded life signs sound a little like recorded radio static from the depths of space. The electrical sig­natures of a human being and a star seemed, in such recordings, not so different, and symbolized our relatedness and indebtedness to the cosmos.”37

Frank Drake and artist Jon Lomberg were tasked with putting together the Golden Record’s photo essay and selecting images that might make sense to a nonhuman species. Lomberg has sent more of his own art into space than perhaps anyone, having de­signed the sundial on the Spirit and Opportunity rovers and cre­ated the Visions of Mars DVD attached to NASA’s Phoenix Lander as a message to future generations who explore the red planet. For Voyager’s record, Drake and Lomberg compiled 115 photos and diagrams depicting insects, wildlife, ballet dancers, bushman hunt­ers, various landscapes, architecture, an X-ray image of a hand, a radio telescope, the Earth in space, an astronaut space walking on orbit, and even a sunset, chosen in part to illustrate Earth’s beauty and because “the reddening of the light contains informa­tion about our atmosphere.”38

The elegantly etched aluminum cover of Voyager’s record indi­cates how the record is to be played and is Lomberg’s work as well. On the right of the cover are illustrations of the appropriate verti­cal to horizontal ratio for television images of the photographs and what the first image, a simple circle, should look like. On the left are top-down and side view graphics showing proper place­ment of the enclosed stylus and the correct rpm speed in binary. The Golden Record is not a conventional 33 1/3 rpm long play­ing record, as is often claimed. Wanting to include as much data as possible, the committee realized they could embed more music and images if they slowed the playtime to 16 2/3 revolutions per minute. Near the bottom right of the record cover is a diagram to indicate that the transition period of a hydrogen atom between its two lowest states, 0.7 billionths of a second, should be taken as equivalent to 1 in binary code. This is intended to give an accurate speed for spinning the record and for interpreting the pulsar map at the bottom left that depicts our Sun relative to 14 pulsars whose precise periods are notated in binary code.

The committee was adamant about sending music as a form of art, particularly since music expresses a potentially universal, mathematical language. But with only a ninety-minute segment dedicated to music, agonizing decisions had to be made in repre­senting musical genres of the world. Hurtling into the depths of space are selections, among others, of Javanese gamelan, an ini­tiation song from Zaire, Japanese shakuhachi, a raga from India, Melanesian panpipes, panpipes and drum from Peru, a Bulgarian shepherdess song, a Navajo Night Chant, tribal music from New Guinea, Louis Armstrong performing jazz, Chuck Berry playing rock and roll, and classical selections by Mozart, Bach, Stravin­sky, and Beethoven. Also included is the Cavatina movement of Beethoven’s String Quartet No. 13 in B Flat, Opus 130, along with an image of sheet music from this selection. It was a piece that Beethoven so cherished he once told a colleague he could cry when thinking of it.39 In researching Beethoven’s Cavatina, Druyan found on the score of an adjacent opus that the composer had written: “What will they think of my music on Uranus? How will they know me?” Beethoven apparently, comments Druyan, “toyed with the thought that his music might leave [our] planet.”40 His intuitive query seems indicative of an artist who saw far beyond his time. For that, and for his deafness, he was often misunder­stood or considered eccentric. While reworking the finale rejected by his publisher for the String Quartet No. 13, Beethoven appar­ently strolled through fields waving his arms, shouting and likely singing, certainly in an attempt to feel since he could not hear, the music playing in his mind and that he found so compelling. So, it seems a perfectly harmonious outcome that Beethoven’s music indeed traveled to Uranus and at this moment, aboard Voyager, is barreling into the pristine interstellar void.

In the introduction to the stunning coffee table volume Saturn: A New View, Kim Stanley Robinson comments on the amazing photographs Cassini has archived in its ongoing exploration of Saturn. Noting that “the gorgeous concentricities of Saturn’s rings look like gravitation itself made visible,” Robinson is wistful that astronauts have not yet journeyed to Enceladus or Titan. “Even­tually, we might even go to Saturn ourselves,” writes Robinson, “It would be a kind of pilgrimage: it would be a sublime experi­ence.”50 However, roboticist Rodney Brooks would likely argue that we have already journeyed to Saturn and landed on one of its moons. NASA’s planetary missions are extensions of ourselves. These little machines, with the ability to travel billions of miles across the chasm of interplanetary space, enhance our vision—like a pair of contacts or glasses—and extend our sense of touch, our ability to sample the atmosphere of another world. Analogous to cochlear implants, pacemakers, or titanium prosthetic legs that allow paraplegic athletes to run faster than Olympians, Cassini has taken us to the far shores of the outer Solar System and con­tinues to record, in fine detail, the state of affairs at Saturn and its moons. Cassini, like our other planetary science missions, serves as a highly technical extension of humankind. These robotic ex­plorers not only extend our fingertips into the frigid outer Solar System, but Brooks argues that our machines are “us,” and that biotechnology of the future will reconfigure what we think of as human. “Our machines will become much more like us, and we will become much more like our machines,” predicts Brooks. “The distinction between us and robots is going to disappear.”51

Futurist Ray Kurzweil couldn’t agree more. Kurzweil predicts that in the next thirty years we will use biochemistry, biotechnol­ogy, and nanotechnology to reconfigure the human body, in part, by readily incorporating technology into our bodies to enhance longevity and our intellectual capacity. Kurzweil points to the evo­lution of sight to illustrate how technology has exponentially en­hanced our biological capabilities:

There are many ramifications of the increasing order and complex­ity that have resulted from biological evolution and its continuation through technology. Consider the boundaries of observation. Early biological life could observe local events several millimeters away, using chemical gradients. When sighted animals evolved, they were able to observe events that were miles away. With the invention of the telescope, humans could see other galaxies millions of light-years away. Conversely, using microscopes, they could see cellular-sized structures. Today humans armed with contemporary technology can see to the edge of the observable universe, a distance of more than thirteen billion light-years, and down to quantum-scale subatomic particles.52

Kurzweil compares this exponential advance in visual observa­tion to the evolution of information technology. He notes that mi­croorganisms can respond to and communicate events in their im­mediate environment, but with the evolution of humans, language, and the technology of writing, we have recorded information that persists for thousands of years. The simple technology of writing, whether in cuneiform or in modern languages, has exponentially expanded our scientific knowledge and reach. Our robotic part­ners in space are no less an extension of ourselves than a telescope or the technology of writing and have powerfully shaped what we know about our planet and the Solar System, and the billions of worlds we have yet to explore.

Even now we are joint explorers with our smart machines. An­thropologist Stefan Helmreich comments, “What it means to do oceanography and ethnography is changing. In an age of remotely operated robots, Internet ocean observatories, multi-sited field­work, and online ethnography, presence in ‘the field’ is increas­ingly simultaneously partial, fractionated, and prosthetic; it is not just distributed across spaces—multi-sited—but cobbled together from different genres of experience, apprehension, and data col – lection.”53 This collaborative scientific exploration, already being undertaken between humans and machines, affords us a kind of distributed intelligence across the Solar System.

Helmreich, Brooks, and Kurzweil suggest that we think of our machines as symbionts, without whose help we could not explore Earth’s ocean depths, much less the depths of lakes and oceans on icy moons orbiting Jupiter or Saturn. Our collaboration with smart machines incites Helmreich to consider one other order of unsuspected collaboration—t hat between humans and microor­ganisms. He suggests that alien microorganisms, if such exist in the frozen ocean on Enceladus or in Titan’s hydrocarbon lakes, may be more akin to life on Earth than we imagine. As microbiologist Jo Handelsman points out, “We have ten times more bacterial cells in our bodies than human cells, so we’re 90 percent bacteria.”54 Of the microbes coexisting in our bodies, scientists explain that we have “evolved with them in a symbiotic relationship, which raises the question of who is occupying whom.”55

In fact, instead of thinking of microorganisms as alien to us, doctors have begun to recruit them in fighting cancer. Research­ers at the University of Pennsylvania are relying on our symbiotic relationship with viruses and other microorganisms to attack and kill cancer cells. They’re using viruses to insert DNA into patients’ T-cells that in turn causes the T-cells to selectively attack and kill cancer cells. As Stefan Helmreich makes clear:

Microbes are not simple echoes of a left-behind origin for humans, orphaned from all evolutionary association. Microbes are historical and contemporary partners, part of our bodies “microbiomes.” “The” human genome is full of their stories. . . . The bacteria that inhabit our bodies do not simply mirror the bacteria that inhabit the sea—as might brine in our blood. This is not human nature reflecting ocean nature. It is an entanglement of natures, an intimacy with the alien. Such dynamics shift the grounds upon which anthropos might be figured, perhaps transforming humanity into Homo alienus.”56

Evidence of this is the fact that people in different regions of the world have different genetic makeup partly due to local microor­ganisms. People of Japanese descent have “acquired a gene for a seaweed-digesting enzyme from a marine bacteria. The gene, not found in the guts of North Americans, may aid in the digestion of sushi wrappers.”57

As noted in the chapter on the Viking mission, Lynn Margu – lis’s contribution to Gaia Theory was to highlight the extent to which our existence is intimately bound up with the Earth’s micro­organisms. Having proposed the theory of symbiogenesis, which claims that the mechanism for evolution is the symbiotic sharing of genetic material, Margulis demonstrated that bacteria invad­ing single-celled organisms became their mitochondria and chlo – roplasts. We do not know whether extremophiles exist on Titan, Enceladus, or other worlds such as Europa, one of Jupiter’s moons. What drives our continued exploration of those distant shores is that our beginnings may be entangled with theirs.

The Greek mathematician Pythagoras imagined a universe de­scribed by numbers. When he talked about the “harmonies of the spheres,” he meant music that enlightened individuals might hear resulting from the translucent shells that carried the celestial objects. Kepler continued this line of thought and applied it to the elliptical orbits of the planets. These ideas sound archaic but they’re not misguided. The universe contains many periodic and oscillatory phenomena, and the formalism to understand them in­volves studying the resulting harmonic frequencies.23 Situations as different as planet, moon, and ring systems and their orbits and interactions, the spiral arms of the Milky Way, and the interac­tions between matter and radiation in the early universe are well described in terms of coupled frequencies and harmonics. We’ve seen beautiful examples of this in the complex gravitational dance of Saturn’s rings and moons, discussed in the Cassini chapter.

A hundred years ago, nobody imagined that the Sun could be studied in terms of harmonics. Apart from the sunspot “blem­ishes,” the surface seemed smooth and featureless. Solar properties vary smoothly through the region we see as the “surface.” The edge marks the distance out from the center at which the density of gas reduces to the point where light no longer interacts with particles and travels freely. Inside this region, which is called the photo­sphere, light is trapped and so the Sun’s interior is hidden from view. The first inkling that the interior was pulsating came when George Ellery Hale built his heliostat on Mount Wilson in the early twentieth century. High-magnification photographs showed a sur­face mottled with fine structure, and time sequences revealed that the Sun’s surface was a seething sea on which the pairs of sunspots floated like large lily pads. The field of helioseismology matured as the century progressed, and solar scientists identified thousands of different oscillatory modes—the Sun “rings” like a bell. The Sun is also like an echo chamber (plate 12). Sound travels through the plasma and sets up standing waves, like the vibrations of the head of a drum or the air inside an organ or woodwind instrument.24

Just as seismologists can infer the internal structure of the Earth from the way sound waves and earthquake tremors pass through the planet, helioseismologists can study the Sun by seeing how in­terior sound waves manifest at the surface. This work has led to measurements of the density, temperature, and chemical abundance of the interior, as well as inference of the age of the Solar System and the constancy of the gravitational constant.25 The workhorse instrument on SOHO is the Michelson Doppler Imager since it shows the oscillations of the entire Sun. This instrument discov­ered a layer about a third of the way to the Sun’s center where the orderly interior, within which energy flows radially, transitions to the turbulent outer region, where energy moves in convective loops. This is the place where the solar magnetic field is created. Just as large-scale flows like the Gulf Stream and the jet stream are important for the Earth’s climate, SOHO data have shown that such flows are important for solar weather.

SOHO’s data is of such high quality that 3D maps of the Sun were derived for the first time. The maps answered questions that puzzled Galileo: how deep do sunspots extend and how can they survive for weeks at a time? The answers: they are fairly shallow but they are rooted in places where the plasma converges and strongly flows downward. SOHO scientists have managed the amazing trick of holographically reconstructing features on the far side of the Sun.26 All these images are available daily on the web. In fact, a plethora of solar data is available online, since a small armada of satellites is monitoring our life-giving star all the time.