Category Dreams of Other Worlds

Scientific discovery rarely unfolds smoothly or predictably. Eight years before the theoretical prediction of relic radiation, Andrew McKellar measured the spectra of stars and discovered interstel­lar material that was excited to a temperature of 2.3 K.17 He had no explanation for the excitation, which is caused by the radia­tion from the big bang.18 While Gamow’s prediction of a universe bathed in cold, microwave radiation sat in the literature, several experimenters had the detection of the radiation within their grasp but either did not control systematic errors well enough or were not aware of the importance of the observation. Robert Dicke at Princeton was, and by 1964 he and his team were hot on the trail of the big bang signature. But as they were preparing a radiometer on the roof of the physics building they got a call from Bell Labs. “Boys, we’ve been scooped,” was Dicke’s memorable response.19 The Nobel Prize was awarded in 1978 to Arno Penzias and Robert Wilson of Bell Labs for their discovery.

What was the nature of the radiation that Penzias and Wilson detected? To understand this involves rewinding the history of the

universe to its very early epochs. The Hubble expansion is a lin­ear relationship between distance and recession velocity: more dis­tant galaxies are moving away from us quicker. Although at first glance this seems to imply that we have a privileged location in the universe, a hypothetical observer in another galaxy would see exactly the same relationship that Hubble saw. In a uniform three­dimensional expansion each observer thinks they are the center of the universe. Since all cannot be, none are. Nor can we see an edge to the universe, so we can’t place ourselves with respect to a boundary. The Copernican principle holds. There’s no discernable center to the universe.

Reversing the expansion projects to a time when all galaxies were on top of each other: the big bang. But a simple backward extrapolation overestimates the age of the universe because matter tugs on other matter, so the expansion rate has slowed since the earliest epochs. In an expanding universe model the major observ­able is redshift, a stretching of the radiation from distant galax­ies due to the expansion of space-time itself. Redshift is simply related to the factor by which the universe has expanded since the radiation was emitted. One plus the redshift is the expansion fac­tor. Ironically, the universe is easier to understand in early times. Before structure forms, the universe behaves just like a simple gas, where the temperature and the average density both increase going back toward the big bang. Once gas starts to collapse by grav­ity, the physics is very complex. Stars and galaxies started form­ing when the universe was about ten times smaller than it is now, about 13 billion years ago.20

Extrapolating further backward, there was a time when the uni­verse was much denser than it is now and hot enough that atoms were ionized. Electrons liberated from atomic nuclei interacted with radiation and stopped the photons from traveling freely. It was as if the universe was shrouded in an impenetrable fog. As the universe expanded and thinned out and cooled, it became trans­parent and radiation could travel without interruption. This spe­cial epoch is the earliest time we can “see” into the universe. In a big bang model, the background radiation comes from a time when the universe was a thousand times smaller than it is today, and a thousand times hotter. Infrared photons from 380,000 years after the big bang, when the temperature was about 3000 K, have been stretched a thousand-fold to become microwave photons in a vast and frigid universe with a temperature a little below 3 K.

The picture of the sky in microwaves is an extraordinary baby picture of the universe. Imagine as an adult that you were shown a picture of yourself a few hours old. Since those waves are from the universe as a whole, they permeate space and they travel in every direction through expanding space. There are trillions of relic photons from the big bang in any volume like that of one breath. However, their radiant intensity coming from any direction in space is only 0.00001 Watt or a ten-millionth of a light bulb.21 If you can find an old-fashioned image tube TV and tune it between stations so you see only static, about 1 percent of the white specks on the screen are interactions of the dots of phosphor with those microwaves.22 The big bang is all around us.

Sometimes the dream is a nightmare. Mars has always had an ominous mien in myth and culture. Ancient civilizations regarded the planet as a malevolent agent of war and apocalypse. Similar myths emerged around the world.1 In late Babylonian texts, Mars is identified with Nergal, the fiery god of destruction and war. To the Greeks, Mars was Ares, one of Twelve Olympians and the son of Zeus and Hera. His attendants on the battlefield were Deimos and Phobos, terror and fear, and his sister and companion was Eris, the goddess of discord.2 Ares was an important but an unlikeable character. In Roman hands he morphed into a virile and noble god, one who facilitated agriculture as well as war. The third month of our year honors him and the time when winter abated enough that Roman legions could begin their military campaigns. In legend, Mars aban­doned his children Romulus and Remus and the twins went on to found the city of Rome.3 The mystique of Mars may have been enhanced by its retrograde motion: the fact that every few years it twice reverses its direction of motion among the stars.4 All exterior planets show this behavior, but the reversal is more dramatic for Mars than for Jupiter and Saturn. It’s curious that such a modest speck of reddish light could exert such power (plate 1).

Fast forward nearly two thousand years and Mars still exerts a grip on the imagination. It’s the night before Halloween, on the eve of World War II. Families across America are settling around the radio to hear “The Mercury Theatre on the Air,” a weekly pro­gram directed by the young Orson Welles and featuring him and

a talented ensemble cast. Listeners are enjoying salsa-inflected or­chestral music from a hotel in New York City when the announcer breaks in: “Ladies and Gentlemen, we interrupt our program of dance music to bring you a special bulletin from the Interconti­nental Radio News.”5 There’s a news report about unusual activity observed on the surface of Mars, then back to the music. A few minutes later the announcer breaks in with additional information about Mars. More music. The next interruption has the announcer talking in breathless tones about a meteor that just landed in New Jersey. A little later, on the scene, there’s horror in his voice as he describes creatures emerging from the meteor, which is in fact a spaceship. The Martians begin using a heat ray to incinerate by­standers, and as the announcer describes the engulfing flames, his voice is cut off in mid-sentence. Welles deliberately scripts several long seconds of silence, or “dead air,” to increase the tension and the verisimilitude.6 In New Jersey and elsewhere around the coun­try, people panic and many load their belongings into cars to es­cape the menace.7

To the modern ear, Welles’s broadcast has the tone of cheesy, B- grade science fiction. But this was a younger, more innocent world, worried about war and ignorant about the improbability of aliens actually visiting Earth. It was nearly twenty years before America would enter the Space Age. In fact, the story of invasion from Mars transcends particulars of time and culture. When H. G. Wells’s novel The War of the Worlds was published in 1898, it was an instant classic. His words retain their evocative power: “Yet across the gulf of space, intellects vast and cool and unsympathetic, re­garded our planet with envious eyes, and slowly and surely drew their plans against us.” More than a century later, when Stephen Spielberg adapted the book for a 2005 movie, the basic plot was unchanged.8 Fear of alien invasion taps into something deep in the human psyche, as primal as dreams themselves.

Water, water everywhere, but not a drop to drink. The most stun­ning finding of the Mars rovers, proclaimed the “Breakthrough of the Year” for 2004 by Science magazine,21 was the evidence for the prolonged presence of salty, acidic, and potentially life-supporting water on the surface. This water has long since disappeared, and climate change on Mars is the leitmotif of all the research done by Spirit and Opportunity. The Viking orbiter had provided sugges­tions of water, but the twin rovers provided indisputable evidence. Below the surface, there are large deposits of ice, with the possi­bility that some of it might be in aquifers kept liquid by pressure and a modest amount of natural radioactive heating from interior

rocks.22

All life on Earth—from the tiniest bacterium to the mightiest redwood tree—needs water. The jury is still out on whether or not Mars has ever hosted life, but within weeks of arriving on the

red planet, Opportunity showed that the Meridiani Planum had once been a water-soaked plain.23 Pay dirt was a stone’s throw from the landing site in the form of a rocky outcropping made of layers about as high as a street curb. The outcrop, nicknamed “El Capitan,” contained numerous clues to a watery past. Opportunity found small hard spheres, called “blueberries” by the science team, which were sometimes loosely scattered on the surface and some­times anchored into rock (figure 3.3). The blueberries were made of hematite, an iron-rich mineral that usually forms on Earth in the presence of water: oxygen atoms from the water bind to iron atoms in the mineral. The team speculated that groundwater car­rying dissolved iron had percolated through the sandstone to form the spheres.24 Later on, Opportunity discovered the mineral called jarosite, which only forms on Earth when acidic water is present.25 Water that’s acidic or rich in dissolved iron is quite capable of

hosting microbial life, as we know from the ecosystems found in places like the runoff from the Rio Tinto mine in Spain.

Opportunity also found inch-high rock layers that overlapped and cut into each other. Geologists call such formations cross-beds, and their sizes and shapes indicated that they had been formed by flowing water. Some layers showed weathering by wind so the water must have been present intermittently. The minerals in the cross-beds were rich in sulfur, chlorine, and bromine, which had apparently settled to the bottom of a salty lake or shallow sea. Similar briny deposits are found in desert regions of the Earth. Op­portunity also found small vugs, from the Cornish word for cave, and these inch-long or smaller cavities were probably left behind when concentrations of minerals were dispersed by groundwater. Mars minerals tell the tale of a watery past.

Meanwhile, Spirit wasn’t spinning its wheels (yet). It had landed in a volcanic, rock-strewn plain with no obvious signs of sedimen­tation, but it soon roamed into its own discoveries. A volcanic rock called “Humphrey” had crevices filled with crystallized minerals that had most likely been dissolved in water. On another rocky target called “Clovis,” Spirit found traces of the mineral goethite, which only forms in a terrestrial environment in the presence of water, and telltale enhancements of sulfur, chlorine, and bromine. Spirit also measured a soil sample with a very high concentration of salt, another indirect indication of water.26 Science always deals with finite or incomplete information so it’s important to rule out plausible alternative hypotheses. The alternative explanation for cross-bedding and other sculpting of the surface is wind erosion, but on Earth the signatures of wind and water erosion are quite distinct. Mars was volcanically active in the past, and volcanism can produce spheres from molten drops and cavities, and occa­sionally minerals like sulphates and jarosite. However, the web of chemical evidence from the rovers, plus the features that can only be explained by the action of water, present a compelling case for an ancient Mars with water on its surface.27

The finding of past water on Mars raises more questions than it answers. Mars has an obliquity—or tilt of its axis as it orbits the Sun—that varies much more than the Earth’s. Orbital tilt causes seasons on any planet. Whereas our tilt is stabilized at close to 23.5 degrees by the Moon, the tilt of Mars is known to have varied from 10 to 60 degrees over the past 100,000 years, and dramatic climate variations were probably occurring in the distant past as well. The idea of a “warmer, wetter” Mars several billion years ago is appealing but is not well supported by climate models and evi­dence from Martian meteorites.28 The problem is that the planet’s modest gravity is incapable of retaining a thick atmosphere, and the early Sun was fainter than it is today. Some 65-70 degrees of greenhouse warming were needed to bring the surface up to the melting point of water, and while Mars did have early volcanism that generated carbon dioxide, which is a heat-trapping green­house gas, the early atmosphere was unlikely to have been thick enough to get the surface temperature above freezing. Mars cli­mate change continues to be enigmatic and difficult to pin down.

Thirty years after their launch and billions of miles from Earth, the Voyager spacecraft continue to transmit data on their way into interstellar space. NASA will track Voyager and listen for its transmissions until the spacecraft fall silent, so that we might learn something about what writer Stephen J. Pyne calls the “soft ge­ography” of the outer Solar System and what lies beyond. Their secondary mission to carry messages of greeting beyond our Sun may, to some, seem futile. Pyne and others have noted the very low likelihood that even if another species came across the spacecraft, they could figure out how to play the phonograph record or even recognize it as a message. Today’s teens, if presented with a copy of Voyager’s record, might find the task difficult, if not impossible. “By the time Voyager reached Jupiter and Saturn,” writes Pyne, “vinyl phonograph records were overtaken by magnetic tapes; by the time it reached Uranus and Neptune, tapes were fast fad­ing before CDs; by the time it reached the heliosheath, CDs were passe compared with digital drives and iPods. The phonograph was hopelessly archaic just as the golden record reached the edge of the solar system—in technology years, barely beyond cuneiform tablets.” As Pyne sees it, the Voyager spacecraft are in many ways ill-equipped for their journey into the unknown: “They were leav­ing the solar system with computer power inadequate to run a cell phone, and electrical power insufficient to animate a clock radio. Yet they had much yet to survey; the dynamics of the solar wind. . . reversals in the Sun’s magnetic field, interstellar particles, radio emissions from various sources within and beyond the he­liosphere, and of course the interstellar medium, if all went well.” However, in spite of Voyager’s technological limits, Pyne describes the spacecraft as the stuff of legend, whose tales will be told in future ages: “For now, it continued to send back reports from new settings. It was doing what no other spacecraft could. Its narrative simply defied closure from Earth.”45

Voyager’s ability to communicate with Earth is certainly lim­ited by its plutonium supply, but like the species that launched it, the spacecraft and its record demonstrate their resilience precisely when faced with seemingly insurmountable limitations. Timothy Ferris, who coordinated the music selections, speculates that even if Voyager’s record is someday retrieved but proves indecipherable, it nevertheless conveys a clear message: “However primitive we seem, however crude this spacecraft, we knew enough to envision ourselves citizens of the cosmos. . . . [W]e too once lived in this house of stars, and we thought of you.”46 Despite the possibility of becoming extinct, and precisely because we might, we sling these auspicious spacecraft into the unfathomable depths out of an innate optimism that runs deep in our species. The odds against another civilization retrieving and playing Voyager’s record are astronomical, and yet we sent them in the recognition that un­derstanding the universe and our place in it has mattered deeply from our earliest beginnings. Voyager’s interstellar mission inad­vertently and silently speaks of two intrinsic human traits: we are relatively physically fragile and, like other species, prone to extinc­tion, and yet we possess an inexplicable capacity to hope even in the most dire circumstances. This instinctual, undaunted ability to hope against all odds must have evolved early on in Homo sapiens as a survival mechanism. So far, it has worked; we are the only extant hominid.

And, such unyielding expectation despite seemingly insurmount­able circumstances has produced some of humankind’s greatest accomplishments. It was that kind of resilience that compelled Beethoven, though completely deaf and fatally ill, to neverthe­less compose some of his most acclaimed works. During Apollo 13, when it seemed the mission and possibly the crew were lost, NASA’s engineers and astronauts refused to give up and brought the crew home via gravity assist. It was with similar abandon and hope that we sent Voyager’s greetings to possible other galactic civilizations. Sagan eloquently illustrates this point: “Billions of years from now our Sun, then a distended red giant star, will have reduced Earth to a charred cinder. But the Voyager record will still be largely intact, in some other remote region of the Milky Way galaxy, preserving a murmur of an ancient civilization that once flourished—perhaps before moving on to greater deeds and other worlds—on the distant planet Earth.”47

The story of life in the universe is a story of stars. As the first clouds of gas formed stars in the infant universe, more than 13 billion years ago, the universe contained only hydrogen, helium, and a few other trace light elements. The nuclei of these light elements were forged in the intense heat a few minutes after the big bang, when the entire universe was as hot as the core of the Sun is now. As the universe rapidly expanded, radiation eased its grip and a scant half million years after the big bang, it had cooled enough for electrons to mate with nuclei and for hydrogen and helium atoms to form. Chemistry was now possible, but a universe made of the two simplest elements is singularly dull—hydrogen atoms can only join to form a hydrogen molecule, while helium is inert.

As the first stars congealed out of the expanding gas, there were no planets because there was nothing to make them out of. There was no life because there was no carbon and no nitrogen and no oxygen.1 Our existence on a rocky planet depends on generation after generation of stars fusing heavy elements in their cores and ejecting them into space to become the raw material for solar sys – tems.2 The fireworks couldn’t start until gravity had used its long reach to gather matter into concentrations dense enough to coun­ter the omnipresent cosmic expansion. This took several hundred million years. But then the pockets of spherical collapse ignited le­gions of stars that could slam atomic nuclei together hard enough for them to fuse and populate the periodic table for the first time.

Every carbon atom in our bodies was once in a star in a remote region of space more than 4.5 billion years ago. Some atoms have cycled through multiple generations of stars; their myriad stories played out over eons until they were co-opted and incorporated into our fleeting human story. We are made of stardust.

Understanding the way in which the products of stellar fusion enriched the nebula that formed the Sun and planets requires finding primordial material in the Solar System. The most pris­tine samples available are certain types of meteorites and comets. There may be as many as a trillion comets and they spend most of their time far from the Sun and Earth in the deep freeze of space. Material from the outer Solar System has been radioactively dated back to 4.567 billion years, which is taken to be the formation epoch. The spherical comet cloud extends to 100,000 Earth-Sun distances and it’s a tenuous relic of the time when the Sun switched on for the first time. In the outer part of their orbits, comets are dark and dead, but they become lively and visible when they ap­proach the Sun. This diaphanous shroud of frozen worlds holds important clues to our origins.

The Aurora Borealis and Aurora Australis occur when electromag­netic particles from the solar wind collide with or excite atoms in the Earth’s magnetosphere (figure 7.4). We now understand the

explicit connection between auroras and magnetic storms, and recently have confirmed the “three-century old theory that auro­ras in the northern and southern hemispheres are nearly mirror images—conjugates—of each other.”38 Very few people in human history have inhabited the high (or low) latitudes where these bril­liant light displays are usually visible. For thousands of years the ethereal, vertical curtains of light, draped from 60 to 200 miles above the Earth’s polar regions, have inspired wonder, as well as poetic and musical responses. The Vikings first recorded the Au­rora Borealis in AD 1250. About seven hundred years later, in 1897, Norwegian explorer Fridtjof Nansen wrote of the north­ern lights: “It was an endless phantasmagoria of sparkling color, surpassing anything that one can dream. Sometimes the spectacle reached such a climax that one’s breath was taken away; one felt that now something extraordinary must happen—at the very least the sky must fall.”39

The twentieth-century composer Edgard Varese worked with “found sound,” incorporating sounds with a non-musical origin

into his music, and with electronic instruments such as the Ther­emin. He once composed a piece based on having seen the Aurora Borealis. His wife Louise recalled in her memoir of the composer, “Nature in its most magnificent and terribly impersonal aspects moved him passionately.” Titles for many of his compositions were drawn from astronomy or science. Of the aurora, Louise writes that Varese claimed he “not only saw but heard” the majestic lu­minescent curtains dancing across the night sky and later notated “the sounds that had accompanied the movements of the light.”40 Electromagnetic waves or natural radio waves can only be detected with a radio receiver.41 If we take Varese at his word, perhaps he experienced some form of synesthesia, so that in fact he had heard the northern lights. In her memoir, Louise Varese speculated that the score of the aurora her husband mentioned was either Les Cy­cles du Nord or Mehr Licht, two of several compositions that were later lost or destroyed.

More recently, Terry Riley and the Kronos Quartet’s chamber music composition Sun Rings, inspired by the Sun’s dynamic mag­netic field, was written to be performed against a backdrop of IMAX-sized images from SOHO and the TRACE (Transition Re­gion and Coronal Explorer) satellite. Riley’s score is accompanied by magnificent sunspots tracking across the face of the Sun as well as finely detailed footage of magnetic field lines breaking through, looping above, and re-submerging into the Sun’s surface. Such con­temporary compositions speak to our deep, primal entanglement with the Sun, which is no less important to our lives now than it was in the ancient past.

From prehistory to the modern era, humans intuitively under­stood the Sun as integral to their very existence. Paleolithic and Neolithic communities scattered across the globe knew that the Sun powerfully shaped their lives. Evidence of their sense of the Sun’s significance is found at the Mnajdra temple on Malta, at Newgrange in Ireland, at Stonehenge on Salisbury Plain, and at many other megalithic structures. Such monuments speak of an ancient past in which peoples from disparate times and places were attentive and accurate observers of our star.

On the island of Malta, just off the coast of Sicily, are the re­mains of a complex of stone temples known as Mnajdra, dating to 5500 BC. One of these limestone edifices marks precise alignments with the Sun during fall and winter equinoxes.42 Physicist Guilio Magli describes Mnajdra as a “stone calendar” marking spring and autumn equinox: “In the course of the seasons, one can follow the movement of the Sun, which rises on the horizon, observing day by day at which point the light strikes the altar inside the tem­ple.”43 In walking through Mnajdra, sited as it is overlooking the Mediterranean Sea, it’s easy to recognize that the location and the megalithic temple were sacred to its ancient architects. Built with cleverness but no metal tools, the effort involved in creating the edifice was prodigious, and a reminder of the investment ancient peoples made in giving homage to the Sun.

Stonehenge, the remarkable structure ancient Britons built on Salisbury Plain sometime between 3015 and 2400 BC, is so well aligned that “the general orientation of the axis of the monument [looks] . . . towards sunrise at the summer solstice in one direction, and towards sunset at the winter solstice in the other.”44 Caroline Alexander observes that, in coming upon Stonehenge, “the great­shouldered silhouette is so unmistakably prehistoric that the effect is momentarily of a time warp cracking onto a lost world.” Alex­ander contends that the architraves atop the monoliths, “bound to their uprights by mortise-and-tenon joints taken straight from carpentry, [are] an eloquent indication of just how radically new this hybrid monument must have been. It is this newness, this as­sured awareness that nothing like it had existed before, this revela­tory quality that is still palpable in its ruined stones.” Though the stone temples at Gobekli Tepe in Turkey are far older and date to approximately 9600 BC, no prehistoric structure like Stonehenge exists anywhere else in the world. Alexander surmises that the Britons who constructed the monument “had discovered some­thing hitherto unknown, hit upon some truth, turned a corner— there is no doubt that the purposefully placed stones are fraught with meaning.”45 Emphasizing the point that the architects delib­erately aligned Stonehenge to mark the winter and summer sol­stices, Magli writes, “This is therefore the only information that the builders left us in writing. Granted it is written in stone, and with stone, and in the language of the sun and of the stones. But it is nevertheless written.”46

Diodorus of Sicily, a Greek historian from the first century BC, supposedly commented on “a lost account set down three cen­turies earlier, which described ‘a magnificent precinct sacred to Apollo and a notable spherical temple’ on a large island in the far north, opposite what is now France.”47 Stonehenge, Diodorus sug­gested, was constructed to pay homage to the Sun. As with the rel­ics of any prehistoric culture, multiple interpretations are possible. Archaeologist Mike Parker Pearson of the Stonehenge Riverside Project has recently reinterpreted Stonehenge as a burial monu­ment. He contends that the people who raised the monoliths on the chalk downs apparently gathered each winter solstice to mark the setting Sun as the beginning of a new year and to remember their ancestors.

Astronomer Edward Krupp has investigated the sophisticated and sizeable burial chamber in Ireland known as Newgrange or Bru na Boinne: “Newgrange is a megalithic surprise,” writes Krupp, who characterizes the structure as emerging from the land­scape “like a highway tourist attraction.”48 During winter solstice at this stone monument, the first rays of the Sun illuminate a room deep in the structure to mark the beginning of the new year. Dat­ing from about 3700 to 3200 BC, Newgrange was designed so that “two weeks either side of the winter solstice, the Sun, on rising, shown down the length of the entrance passage and illuminated the central chamber—as it still does.”49 The beam of sunlight, as it travels deep into the monument, is thinned and sculpted by the megaliths’ calculated placement. To offer a vivid picture of the massive effort required to construct the edifice, Magli emphasizes that “5000 years ago, someone built a monument involving thou­sands of tons of earth and rock, covered it with quartz like a giant jewelry box, [and] carefully measured the direction of the sunrise at winter solstice to line up a corridor built with stones as heavy as many elephants together.”50 Not surprisingly, the legend associated with Newgrange recounts tales of the earliest known Irish gods, “The Lords of Light.”51

The Chankillo complex in Peru predates the Inca by two thou­sand years, offering insight into the precursors to Sun worship among the Inca and their official Sun cult. In 2007, Ivan Ghe – zzi, Peru’s national director of archaeology, and astronomer Clive

Ruggles reported discerning the layout of what is considered the oldest solar temple in the Americas. Ghezzi was first to surmise the purpose of thirteen towers on a ridge near Chankillo, a fourth century BC ceremonial complex in the northern coastal, desert region of Peru. Traditionally considered a fortress, Chankillo is now understood to be a very precise solar observatory built by the people who predated the Inca. Ghezzi realized that the prominent line of stone towers were markers that indicated the Sun’s position throughout the months of the calendar year. He contacted Ruggles and together these researchers, using hand-held GPS devices, de­termined that the location of the towers as projected against the horizon “corresponds very closely to the range of movement of the rising and setting positions of the Sun over the year.” In particular, winter and summer solstice alignments are clearly marked by the towers. Ghezzi and Ruggles have shown that the towers and the gaps between them offered “a means to track the progress of the Sun up and down the horizon to within an accuracy of two or three days.”52

One import of the findings at Chankillo, write Ghezzi and Rug­gles, is that “sunrise ceremonies, at a sanctuary on the Island of the Sun in Lake Titicaca, surrounding a crag regarded as the origin place of the Sun, almost certainly had pre-Incaic roots.”53 Either the Inca, or the peoples who predated them, named an island in Lake Titicaca as Isla del Sol, or Island of the Sun, in honor of the god who created the Sun, Moon, stars, and humankind. It is well known that at the high Andean city of Machu Picchu, constructed in the late 1400s, the Inca kept accurate records marking the win­ter solstice, the first day of the Inca year. But the Inca may have ad­opted their attentiveness to the Sun from peoples who far predated their great civilization.

Long before the Neolithic Britons were raising those remark­able trilithons on Salisbury Plain, the Egyptians had already de­veloped writing and record keeping and were constructing the Great Sphinx at Giza, apparently in recognition of the god Horus or Horemakhet, believed to be a personification of the Sun on the horizon.54 An even earlier instantiation of the Sun god Horus was Ra, the patron god of the ancient Egyptian city Heliopolis, located in the Nile delta. In approximately 2400 BC, Ra was combined with the god of Thebes to become Amun-Ra, the highest deity in the Egyptian pantheon. These are a few of the varied civilizations that recognized the importance of the Sun to their survival. In the Information Age, we’re just as dependent on our star as ancient peoples—maybe even more so.

Even to the naked eye, Mars clearly varies in brightness over months and years. Mars is roughly 50 percent farther away from the Sun than the Earth, and its distance from us depends on which side of the Sun each planet is on and the details of their elliptical orbits. At its closest,9 Mars is only 55 million kilometers away and, at its farthest, it’s 400 million kilometers away. This variation cor­responds to a factor of 50 in apparent brightness and a factor of 7 in angular size. Only the brightness variation is visible to the naked eye; a telescope is needed to resolve Mars into a pale red disk. Even when it looms closest in the sky, Mars is just 25 arc seconds across, or seventy times smaller than the full Moon.

Following the invention of the telescope, the view of Mars evolved relatively slowly. Galileo began observing Mars in Septem­ber 1610.10 He noticed that it changed in angular size and he specu­lated that the planet had phases. The Dutch astronomer Christian Huygens was first to draw a sketch with surface features, in partic­ular the dark area or “mare” called Syrtis Major. Huygens thought Mars might be inhabited, perhaps by intelligent creatures. In the middle of the seventeenth century, Giovanni Cassini and Huygens first spotted the pale polar caps of Mars,11 and in the early eigh­teenth century Cassini’s nephew Giacomo Maraldi saw variations in the polar caps that he speculated were due to water freezing and melting during the Martian seasons, although he could not rule out varying clouds.12 William Herschel used his state-of-the-art tele­scopes for a period of more than eight years beginning in 1777 to bolster the interpretation that the poles were made of frozen water. He had measured the tilt of Mars’s spin axis relative to the plane of its orbit so knew it had similar seasons to the Earth. He had also read Huygens’s posthumous book Cosmotheoros in which the Dutchman speculated about life in the Solar System. In an address to the Royal Society in London, Herschel asserted boldly: “These alterations we can hardly ascribe to any other cause than the vari­able disposition of clouds and vapors floating in the atmosphere of the planet. . . . Mars has a considerable but modest atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to our own.”13 With respected scientists setting up the ex­pectation of life on Mars so long ago, it’s not surprising that the idea had taken deep root by the modern age.

Telescope design continued to improve through the nineteenth century, allowing telescopes to make sharper images and resolve smaller features on Mars. In 1863, the Jesuit astronomer Angelo Secchi saw the maria appear to change in color; he fancifully drew them as green, yellow, blue, and brown at different times. He also saw two dark, linear features that he referred to as canali, which is Italian for grooves or channels.14 It was a fateful choice of words, because the literal English translation as canals suggests construc­tion by a technological civilization.

Behind every successful robot rover there’s a driver. Actually, four­teen drivers in the case of Spirit and Opportunity. For those peo­ple used to the gray, male gristle of the typical scene at Mission Control in Houston, the rover drivers are surprisingly young, and many are women. Drivers don’t control the rovers in real time with a joystick; the reasons are that real-time control would be far too hazardous, and there’s no immediate feedback. Depending on where the Earth and Mars are in their orbits, the distance can vary from 35 to 200 million miles, and the time delay for a signal can be as high as twenty minutes.

The drivers are part of a much larger team of engineers and scientists, numbering over two hundred, who are all involved at some level in what the rovers do. On a typical day, the results of the previous day—which are part of a larger strategy involving weeks or months of roving—are evaluated as quickly as possible, usually within an hour. Then the drivers work with the science team to map out the day’s activities, which might involve measure­ments of an interesting rock or navigating around obstacles. This is turned into a set of commands that the rovers can execute. Com­mands are turned into a realistic animation and reviewed with the science team. Then they are picked apart for anything that could go wrong. All possible contingencies are considered. The final list of commands is reviewed twice and sent to the rovers to execute. Then the process starts again, as it has for over 2,500 days. The only break comes during each Martian winter when the rovers hibernate and conserve power.

There’s a catch. A Martian day is 40 minutes longer than a Ter – ran day. So each day drivers begin their days 40 minutes later than the day before. As driver Scott Maxwell has said, “Pretty soon, you’re starting your day at midnight, at 2 a. m., at 4 a. m. (figure 3.4). It’s been called ‘Martian jet lag’—it’s tough on bodies, on brains, on relationships.”31 It leads to fatigue, which leads to mis­takes. So many drivers watch their caffeine intake and keep to Mars time even on their days off, which puts further strain on relationships and adds to the “otherworldliness” of the job. As for what it feels like to control a robotic vehicle on another planet, listen to Ashley Stroupe, one of the most experienced drivers: “It’s really just awe inspiring. Probably the closest I’ll ever get to being an astronaut. Going to new places and being the first human eyes to see them is profound and hard to describe. It’s the best job I could imagine.”32

The different personalities of the rovers project into the driving experience, as Stroupe explains: “The rovers do behave differently!

Spirit and Opportunity are first in very different terrains, and so you have to drive them differently. Also, they have aged differently and have driven us to use very different strategies. We have to drive Spirit mostly backward to drag the broken right front wheel, and we have to drive Opportunity with the robotic arm out in front since one of the joints broke and we can’t stow it anymore.” There are also light moments, as Maxwell describes in his online blog: “Early in the mission, we nearly lost Spirit due to a problem with its flash file system. When we’d diagnosed and fixed the problem, cleaned up the flash drive, and knew that the danger was past, someone wrote this on one of our white boards: Spirit was willing, but the flash was weak.” His greatest driving challenge was trying to get Spirit to a safe haven for the winter by driving across a dune with a balky wheel. As he said, “Imagine trying to cross a desert pushing a shopping cart with one stuck wheel.”

All human cultures communicate by signaling greetings, which serve as an opening that usually indicates a lack of hostility. Whether a presidential address, evening news program, a letter, telephone message, or a friend or stranger’s passing acknowledg­ment on the street, we anticipate salutations.48 Greetings also are an opening to what the ancient Greeks called xenia, hospitality to the unknown other. Biocultural theorist Brian Boyd contends that among ancient Greek cultures, the extension of hospitality, or xenia, initiated collaboration among strangers in a hostile time and region. Particularly in the Iliad and Odyssey texts, hospitality, asserts Boyd, is a core value:

The word xenos, stranger-guest-host-friend, tells a whole exemplary tale in a single word. When a stranger arrives at my doorstep, I am obligated to welcome and feed him. . . even before asking him who he is. . . . The stranger becomes my guest, and to signify that he has therefore also become my friend, I should bestow on him a valuable gift at his departure, and help him on his onward journey. He is then obliged, should I arrive on his threshold, to become my host. . . . But more than that: the bond of xenia created by the initial act of welcome and cemented by the gift should endure between us for life and be­tween our descendants.49

As an example of this, Boyd mentions a scene from the Iliad in which a Greek and a Trojan warrior refuse to fight as their rela­tives were xenoi.

From its inception, Voyager’s Record was understood to be as much a message to ourselves as it was to those who may encoun­ter it. Included are greetings from President Jimmy Carter, who wrote: “This is a present from a small distant world, a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations.”50 Even as Voyager ex­tends hospitality to possible galactic civilizations, Carl Sagan often reiterated that we must extend to neighboring nations, those we know quite well, an equal largess if we wish to survive millions of years hence. That was the point of Sagan’s talk given in 1988 on the 125 th commemoration of the Battle of Gettysburg:

Today there is an urgent, practical necessity to work together on arms control, on the world economy, on the global environment. It is clear that the nations of the world now can only rise and fall together. . . . The real triumph of Gettysburg was not, I think, in 1863, but in 1913, when the surviving veterans, the remnants of the adversary forces, the Blue and the Gray, met in celebration and solemn memorial. It had been the war that set brother against brother, and when the time came to remember, on the 50th anniversary of the battle, the survivors fell, sobbing, into one another’s arms. They could not help themselves.51

Though seemingly ill-equipped for their mission, Voyager carries from a tiny blue dot of a planet into the unfathomable abyss a gift, a small repository of human artifacts, music, and greetings offering not just xenia but charity that neither expects nor re­quires reciprocity. That was the attribute that ensured our survival as a species and likewise has informed our dream of becoming members of an advanced galactic community. “In their explor­atory intent,” wrote Sagan, “in the lofty ambition of their objec­tives, in their utter lack of intent to do harm, and in the brilliance of their design and performance, these robots speak eloquently for us.”52

Aerogel was created in 1931 as the result of a bet. Steven Kistler wagered a colleague that he could replace the liquid inside a jam jar without producing any shrinkage. In other words, he thought he could fill the volume with something that had the same struc­tural properties but was completely dry. The material that won the bet was 99.8 percent air and has the lowest density of any known solid. Aerogel is made by extracting the liquid from a gel by super­critical drying. This allows the liquid to be slowly drawn off with­out the solid matrix of the gel collapsing under its capillary action, as would occur during evaporation. The first aerogels were made of silica; more recent ingredients include alumina and carbon.11

If you touch an aerogel, it feels like Styrofoam or the green foam that flowers are often pressed into. Pressing on it softly doesn’t leave a mark and pressing on it firmly leaves a slight depression. But pressing down sharply enough will cause a catastrophic break­down of the dendritic structure, making it shatter like glass. It’s light and strong, supporting four thousand times its own weight. Aerogel is a thousand times less dense than glass, and the myriad tiny cells of air trapped inside the material make it one of the best insulators known. Engineers at NASA’s Jet Propulsion Lab learned how to make extremely pure aerogel and it was used as an insula­tor on the Mars Pathfinder mission. Peter Tsou is the wizard at JPL who fabricates aerogels; because of the importance of his skills, he was named deputy principal investigator on Stardust.

With Stardust, the challenge was to capture small particles mov­ing at six times the speed of a rifle bullet without vaporizing them or altering them chemically. Aerogel is perfect for this job; the rigid foam that’s not much denser than air slows the particles down and brings them to a relatively gentle halt, each one leaving a carrot­shaped wake two hundred times its size. Imagine firing bullets into a swimming pool filled with Jello. Stardust’s aerogel was fitted into a module the size and shape of a tennis racket that swung out when the spacecraft approached the comet. One side was turned to face Wild 2, and the other side was turned to face interstellar dust encountered on the journey. Before and after use, the module was stored in its protective Sample Return Capsule (plate 9).12

Stardust flew within 150 miles of the comet on January 2, 2004 and headed back to Earth with its precious cargo trapped like tiny flies in a silica spider web. On January 15, 2006, Stardust returned home after seven years and nearly 3 billion miles of traveling. First, the mission controllers did a short rocket burn to divert the space­craft from hitting the Earth, leaving it with just 20 kg of fuel. Then they fired two cable-cutters and three retention bolts to release the 46-kg return capsule and watched as springs on the spacecraft pushed the capsule away. The capsule streaked into the pre-dawn California sky at 29,000 mph, faster than any man-made object had ever been returned to Earth. The heat shield and parachutes worked flawlessly and the capsule landed in the Utah desert at 5:10 a. m. The few people up and outside that morning saw a fire­ball and heard a sonic boom.

Within two days, the package containing the aerogel was opened in a clean room at the Johnson Space Center in Houston. Stardust was subject to the maximum contamination restrictions, since it returned material from an extraterrestrial object with the potential to host life. In practice, the risk of “infecting” the Earth with alien life was low, since any known organism would almost certainly be destroyed by the high impact speeds in the aerogel, but NASA took no chances. The mission was carried out under a Category 5 plane­tary protection policy, which is even more stringent than Biosafety Level 4, the protocol used to deal with hemorrhagic fevers like Ebola and Marburg.13 That means sterilization by heat, chemicals, and radiation before the spacecraft is launched, and a requirement that the returned samples are handled in a secure facility and never come into direct contact with humans.

Members of the team opened the sample return package in a clean room just down the hall from where hundreds of kilos of Moon rocks are kept, brought back by the Apollo astronauts.14 The room was a hundred times cleaner than a hospital operating theater. They were delighted to see the aerogel segments littered with particle tracks, looking like burrows left behind by micro­scopic creatures. The mission had clearly been a success.