Category Dreams of Other Worlds

Humans have always been aware that the Sun’s rays sustain life on Earth. But until the invention of the telescope, the Sun was thought to be smooth and pristine. There’s some evidence of naked-eye ob­servations of sunspots in China as early as 28 BC, and possibly sev­eral centuries earlier.3 Aristotle’s strong supposition that the heav­ens were perfect meant that sunspots probably went undiscovered in Europe for nearly two thousand years. Galileo saw sunspots in 1610 and noticed that they rotated with the Sun. Jesuit astronomer Christoph Scheiner also observed them soon after, and he believed them to be orbiting satellites.4 But by 1630, Scheiner had aban­doned his Aristotelian view and accepted that sunspots rotated at different rates, faster at the equator and slower at the poles. This proved that the Sun couldn’t be a solid object but was more prob­ably composed of gas or liquid. Through the seventeenth century, the number of sunspots declined almost to zero, giving a first hint of the Sun’s effect on our weather, as a period of low sunspot num­bers called the Maunder minimum corresponded to decades when Europe went into a deep freeze, with southern England ice-bound and people in Holland skating on the frozen canals all summer. It wasn’t until the 1840s that Heinrich Schwabe discovered that sun­spot numbers varied with an eleven-year cycle (figure 7.1).

Figure 7.1. Sunspots have been systematically counted since the invention of the telescope. There was an extended “Maunder minimum” of sunspot numbers soon thereafter, which corresponded to a period of very cold climate in northern Europe. This was an early indication of the possible connection between Sun variation and climate (NASA/David Hathaway).

Around the same time that Galileo was doing his pioneering work with the telescope, William Gilbert recognized that the Earth had a magnetic field similar to the dipole field of magnetized rocks called lodestones. Over the next several hundred years, scientists explored the Earth’s invisible magnetic field and showed that it fluctuated in ways that seemed to depend on the Sun. In 1777, Jo­hann Wilcke noticed that auroral rays in the polar regions lay along the field lines of Gilbert’s dipole. Then, in 1859, two scientists ob­served a white light flare on the Sun, followed two days later by a geomagnetic storm on the Earth.5 This once-in-a-millennium event caused aurorae all around the world, including places that had never experienced such a phenomenon in human memory, such as the Caribbean. The northern lights were so bright in the North American Rockies that miners ate breakfast, convinced that the day had started. Telegraph systems failed worldwide and operators reported that they received severe shocks by sparks leaping from the equipment.

Coincidences like this were provocative, but they didn’t amount to an explanation. In 1896, Norwegian scientist Kristian Birkeland devised an elegant experiment where the Sun was represented by a cathode and the Earth by a spherical, magnetized anode. With both situated in a large vacuum chamber, he watched as the appa­
ratus behaved like a miniature Earth-Sun system, with an electrical discharge like an aurora occurring at high geomagnetic latitudes. Not long afterward, George Ellery Hale built the first instrument to study solar flares in detail, on Mount Wilson in California, and he confirmed the two-day lag between flares and geomagnetic storms on Earth. Hale proved that sunspots were magnetized—the first detection of magnetic fields beyond the Earth. He also showed that the polarity of sunspot pairs is the same within a cycle, but reverses from one sunspot cycle to the next.6

Many researchers have looked for correlations between sun­spots and weather on the Earth. Sunspots are actually cooler than the area around them, because the tight bundle of magnetic field lines that they contain restricts the convection that carries heat up from the solar interior. How, therefore, could a sunspot minimum correspond to colder temperatures on the Earth? In part it’s be­cause the area around a sunspot is brighter than an average patch of the Sun’s surface (figure 7.2). So the Sun is brighter when there are more sunspots. But that still leaves a mystery. When scientists developed digital detectors in the 1970s, they found that the full variation of the Sun’s brightness over a sunspot cycle was only one part in a thousand, or 0.1 percent, not nearly big enough to explain significant temperature variations on Earth. The Maunder Minimum aside, there’s no convincing evidence that the sunspot cycle drives non-s easonal climate change, especially the rise in global temperatures over the past half century.7

However, the variations of the Sun in invisible forms of high – energy radiation are much more extreme than its variation in vis­ible light. Moreover, space isn’t the simple and absolute vacuum that most scientists once imagined. Fifty years ago it was shown that the Sun is surrounded by a vast region of plasma, a diffuse, magnetized gas so hot that the particles are traveling near light speed. The stream of particles emerging from the Sun—the solar wind—travels millions of miles to us, where it hits and distorts the Earth’s magnetic field.8 Even though the nature of the ef­fects is complex and subtle, the Sun and Earth are one connected system.

In a sense, not much has changed since ancient humans first looked toward the skies. Astronomers today are equally compelled to in­terpret the patterns in the stars within our galaxy and beyond. In late 2013, ESA plans to launch its next astrometry mission with the Gaia spacecraft (Global Astrometric Interferometer for Astrophys­ics), which will expand the work of Hipparcos.54 The Gaia mis­sion, however, will be far more extensive and accurate in its survey of stars, taking in data on a thousand million stars in the Milky Way, charting the position, distance, brightness, and movement of each one (figure 8.5). It will achieve this by using much larger mir­rors than Hipparcos and much more sensitive CCD detectors. Its goal is a precision of 20 micro-arcseconds for stars at magnitude 15, or 10,000 times fainter than the eye can see, and 200 micro – arcseconds for stars at magnitude 20, or a million times fainter than the eye can see. To extend an earlier analogy, the smaller of these tiny angles would be formed by drawing lines from the top and bottom of Lincoln’s eye on a penny in New York and having them come to an apex not in Paris but on the surface of the Moon!

It is anticipated that Gaia will measure and characterize several thousand exoplanets, detecting them by the subtle motion they in­duce in their parent star. Among these distant worlds, some that are Earth-like must surely exist. However, Gaia’s primary mission will be to produce an extraordinarily precise three-dimensional

map of the Milky Way galaxy and sharpen the crispness of our 3D view.55 As explained on the Gaia website, “In the process, Gaia will also map the motions of stars, which encode their origin and subsequent evolution. Through comprehensive photometric classi­fication, Gaia will provide the detailed physical properties of each of the billion stars observed.” Such information will include data on luminosity, temperature, gravity, and elemental composition, which can be used to unravel information on the origin, structure, and evolution of our galaxy. “Gaia’s expected scientific harvest is of almost inconceivable extent and implication. . . . Amongst other results relevant to fundamental physics, Gaia will follow the bend­ing of star light by the Sun, over the entire celestial sphere, and therefore directly observe the structure of space-time.” As a means of comparison with its predecessor, Gaia planners note: “The 16 volumes of Hipparcos would instead be 160,000 volumes and in­stead of filling one normal bookshelf, that bookshelf would have to stretch the equivalent distance of Paris to Amsterdam.”56

Perhaps most important, Gaia will dramatically alter our sense of humankind’s place in the Milky Way and in the universe. Far exceeding the Apollo 8 image of “Earthrise from the Moon,” or the Apollo 17 image of the “Whole Earth,” the Gaia mission has the potential to entirely overhaul our thinking about our grain of sand, the Earth, in the chasm of interstellar space. Astronomers have already discussed the extent to which the mission will pow­erfully impact nonspecialist audiences. In the coming decade, our children will have the opportunity to see in exquisite detail where we are in relation to our nearest star neighbors as educators plan virtual astronomy courses for educational institutions and plan­etaria. Based on new and rich data from Gaia, virtual flights into a 3D version of a larger portion of the Milky Way galaxy are just one of the expected educational outcomes.57 With Gaia, and the virtual galaxy its data will help build, the scientific and public un­derstanding regarding our place in the Milky Way is poised to be radically reconfigured.

Roughly half the world’s population live in urban areas. Light pollution inherent to cities means that 50 percent of humankind has to a large extent lost access to, and knowledge built upon, the night sky. However, scientific missions like Hipparcos and Gaia are restoring our relationship to the stars and generating remarkable new knowledge regarding Earth’s place in our galaxy. Hipparcos has already rewritten the narratives we will tell our children about the past and present morphology of the Milky Way and the exo­planets we are currently finding orbiting nearby stars. What Gaia promises to contribute will rewrite the textbooks again. The story of our galaxy that we hand on to future generations will disclose the number and locations of many other worlds like ours and will inevitably be vital to the human narrative of future ages.

By the late twentieth century, Mars emerged as the familiar land­scape we recognize and cherish. Unlike Mercury, Venus, or even our own Moon, Mars has come into full relief. It is as if a Mercator’s projection of Mars has lifted from its paper and rounded into a globe with tangible polar ice caps, soaring volcanoes, immense rift valleys, recognizable craters, and plains of crescent barchan dunes. Our robotic partners have added these features of Martian terrain to the iconic landscapes that preoccupy, and persist in, the human imagination. Images sent back by Mariner, the Viking Orbiters, Mars Global Surveyor, and Mars Reconnaissance Orbiter allow us to turn the globe of Mars in our hands, so to speak, and trace the planet’s volcanoes, its broken and unzipped canyons, and its ancient and desiccated river beds.3 With the Mars Exploration Rovers Spirit and Opportunity, we’ve explored in fine detail Victoria, Gusev, and Endeavor craters and captured our closest view yet of the red planet. Asked to name a landmark on the Moon, most people would prob­ably answer the Sea of Tranquility, the landing site of Apollo 11. A few might mention the lunar Apennines, landing site of Apollo 15. But ask most fifth graders about Olympus Mons, Tharsis Bulge, or Valles Marineris and they not only readily reply, but also immedi­ately envision these remarkable topographic features.

With a fleet of NASA planetary missions perusing the Solar Sys­tem, by the late twentieth century “near space” emerged as a set of familiar landscapes. Serge Brunier comments that “the deserts of Mars and the rings of Saturn are as familiar to us today as the most awe-inspiring landscapes of our own planet.”4 Cultural geog­rapher Denis Cosgrove similarly has observed that the “differenti­ated surfaces” of the Moon, Mercury, and Mars “are increasingly present” to us and have become a valued aesthetic to scientists and general audiences alike. As the planetary landscapes of our Solar System settle into the imagination, Cosgrove explains that this terrain has evolved into places of “detailed human understand­ing and care.”5 He equates our familiarity with lunar or Martian panoramas or the surfaces of Saturnian and Jovian moons with the crude maps and charted rocks that seafarers used to cross the open ocean. For the earliest mariners, horizon markers, if only the for­bidding and jagged edge of a dangerous coast, would have been a welcome sight, waypoints indicating location and direction. Even a handful of recognizable land or sea features made the seemingly blank and formidable marine expanse less threatening and more navigable. Passes and shorelines, mapped and remembered, altered our relation to Earth’s globe. The currently unfolding planetary geographies are again reconfiguring our sense of place, this time in relation to the Solar System itself.

Of all the planetary geographies beyond those of Earth, Mars’s iconic features are perhaps the most familiar and deeply embed­ded. Viking 1’s initial glimpses of a rock-strewn plain rising to a salmon-colored sky surprised and delighted us, as did the frost – covered rubble of Utopia Planitia photographed by the Viking 2 Lander. With its Arizona-like desert terrain, and dust devils danc­ing lazily over seemingly endless rock fields, Mars has become a place we know, remember, and dream of exploring. Even now, teams of scientists practice working in Mars-analog environments such as the Mars Society’s Desert Research Station in Utah, or the barren and desiccated salt pans of Chile’s Atacama Desert. In a valley near the Atlas Mountains in Morocco, scientists are study­ing the landscape in preparation for ESA’s ExoMars mission.6 Re­search at these sites is focused on developing new technologies necessary for exploring Mars with a geologist’s hands and eyes.7 Until a mission manages to place astronauts on the Martian sur­face, we linger over coffee table volumes from which spill its alien terrain of jagged and scalloped craters, hanging canyons, and high clouds clinging to volcanic summits.

Jim Bell’s Postcards from Mars vividly illustrates why we are so captivated by the red planet. Multi-page panoramas tumble open to a sunset glimpsed by Spirit from the rim of Gusev Crater, and of Opportunity’s sweeping view of Endurance Crater, with its angu­lar dunes a meter in height. A day on Mars, or Martian sol, is not so different from that on Earth, about 24 hours and 37 minutes. Like Earth, Mars has seasons due to its similar axial tilt, polar ice caps, and a year of 687 days. Bell, however, clarifies that while its landscape in appearance resembles Earth’s desert terrain, atmo­spheric conditions on Mars are nothing like the world we inhabit. Having served as the landscape photographer and primary camera operator for the MER rovers, Bell was responsible for processing and interpreting images from Spirit and Opportunity’s panoramic cameras or pancams. Of the Mars he has so patiently and tirelessly photographed and rendered, Bell writes: “There’s an ‘I’ve seen that place before’ feel of looking out the window across a long drive in the desert somewhere. Rocks, hill, sky—it’s all very Earthlike and comforting, in a way. But it’s an illusion. It’s 30 to 50 degrees below zero (°C or °F, it doesn’t matter) on average out there; the air is almost entirely carbon dioxide, with only a trace of oxygen; and it hasn’t rained in something like 2 to 3 billion years, if ever.”8

Panoramas taken by the rovers’ pancams, specially designed to capture Mars in spectacular detail, called for hundreds of photos to be carefully stitched together for a single panoramic view.9 “I wanted them to be postcards—views showcasing the beauty of the natural environment that we now found ourselves in,” writes Bell. “We even set the first few mosaics up to be rectangular in shape, just like postcards.” Photocomposition requires proper interpreta­tion with regard to color under Martian sunlit conditions and is driven by both aesthetic and scientific objectives.10 For instance, in the first image Spirit took of its landing site, Bell noted scuff marks in the Martian soil made by cables that retracted the lander’s air­bags: “The scratches looked very strange, though, like someone had taken a carpenter’s plane and dragged it across the ground, so that pieces of soil were lifted and curled up like wood shavings. A place that at first glance seems commonplace turns out to be quite alien after all.” Large, sweeping vistas taken by Spirit and Opportunity have afforded greater understanding of water deposition, erosion, as well as aeolian processes, and further demonstrate that Mars is a planet of ever-evolving geomorphology.11 When, for instance, the rover team wondered about the frequency of dust devils, Bell ordered the rovers to lie in wait and record what might pass the camera lens: “Within days we started catching dust devils moving across the plains in the images. Over the course of months of oc­casional monitoring we saw hundreds of them. . . . As the plains got warmer with the advance of the seasons, it became clear that these mini-storms are a major way that dust gets moved around on Mars.”12 Fortuitously, the dust devils happened to clean the rovers’ solar arrays, inadvertently extending their lives for years.

Driving the rovers over broad stretches of terrain reminds us of the grave challenges of Martian exploration, for robotic or human explorers. During the fall of 2004, when the Sun had shifted far­ther North and its light was less direct, Spirit was trekking as far as possible each day, depending on battery reserves. Bell recalls, “When we drove or parked, we had to try to bask, lizard-like, with the panels tilted as much into the Sun as possible to maximize our power supply.” He recounts how the rover team targeted pre­selected “lily pads” on slopes that would catch the most sunlight. Late in 2005, while parked on Husband Hill, Spirit took some time away from its geological scrutiny to look upward and make a few astronomical observations. There, along with the rover, Bell recorded “curving star trails, potato-shaped moons moving in the night, shooting stars, the setting Sun, and the rising Earth [as] fa­miliar, yet alien and evocative.”13

It was detailed images of the Martian landscape sent back by the Viking orbiters and landers that enticed Steve Squyres to be­come a planetary scientist. Principal investigator for the MER mission, Squyres recounts how in 1977, as an undergraduate at Cornell University, he became entranced with Mars’s stark ter­rain. He signed up for a graduate seminar to be taught by one of the Viking project scientists and ended up gaining access to the “Mars Room” in Clark Hall that housed the pictures stream­ing in from Viking. While some of the images had been collected into notebooks, the majority, Squyres noted, “were on long rolls of photographic paper, stacked on the floor or still in their ship­ping cartons.” Looking to uncover in a matter of minutes some hook for a course assignment, Squyres quickly became captivated by the alien landscape unfolded before him in photos that he real­ized even scientists had not yet digested. He found himself poring over image after image—for the next four hours. “The planet that I saw in those pictures is a beautiful, terrible, desolate place,” wrote Squyres, who recalls stepping “out of that room knowing exactly what I wanted to do with the rest of my life.”14 Squyres’s journey to exploring Mars resulted in NASA’s twin rovers Spirit and Op­portunity that in turn have captivated the world’s next generation of planetary scientists and explorers.

Mission “creep” is NASA jargon for the situation when new goals or capabilities (and usually extra associated costs) are added to a mission as it is being developed. The phrase has negative connota­tions, but the Voyager spacecraft wear it as a badge of honor. Their original two-planet mission was designed to last five years. With all the objectives for Jupiter and Saturn achieved, flybys of the two outermost planets—Uranus and Neptune—proved irresistible to mission planners. The five-year mission extended to twelve. As the spacecraft moved into uncharted territory, the time it took for a round-trip signal to be sent from JPL stretched to more than a day, so engineers figured out how to program the Voyagers for remote control, allowing them to be more autonomous. Now the mission has been running long enough that the Voyagers may outlive many of their designers. As the Voyagers recede from Earth, the mod­est power sent back with their high-gain antennas dilutes through an ever-larger volume of space. Currently, the deep-space tracking network detects a minuscule 10-16 Watts (equivalent to a billion billionth of a light bulb) from each spacecraft.22

What lies beyond the Solar System? Uranus is at 30 A. U., or thirty times the Earth-Sun distance. From 30 to 50 A. U. lies a vast ring of debris similar to the Asteroid Belt. Called the Kuiper Belt, it contains about 100,000 rocks larger than 30 miles across, in­cluding some dwarf planets.23 Where the Solar System ends and interstellar space begins is a matter of argument. The Sun sends high-energy charged particles out from its upper atmosphere in all directions. This solar “wind” streaks past us at a speed of a million miles per hour and creates an evacuated region or bubble called the heliosphere. The heliosphere extends past all the planets and ends when the solar wind runs into the rarified gas of hydrogen and helium that permeates the regions between stars in the Milky Way. A shock wave is created as the rapidly moving wind slows to subsonic speeds. The location of this boundary layer is one of the big unanswered questions in astrophysics.

The Voyagers have several ways to diagnose the invisible pro­cesses that take place in the near vacuum of the outer Solar Sys­tem. They can study the strength and orientation of the magnetic field of the Sun, the composition, direction, and energies of solar wind particles, and the strength of the radio emission from be­yond the heliosphere. At the boundary is the place where the solar wind slows suddenly from a speed of 1 million miles per hour and becomes a lot denser and hotter. In December 2004, Voyager 1 crossed this shock.24 A few years later, Voyager 2 followed its twin into the unknown. Recent results have been surprising. The edge of the Solar System isn’t smooth but is filled with chaotic mag­netic bubbles 100 million miles wide. These bubbles are formed when the Sun’s distant magnetic field lines reorganize and form separate structures. Until this observation, it had been expected that the space far beyond the Sun would be smooth and feature­less. In December 2010, Voyager 1 saw the outward speed of the solar wind particles slow to zero. Stagnation of the solar wind was unexpected and may mean that the spacecraft are on the verge of entering a new realm, the vast space between the stars.

Voyager is as ambitious as any project humans have under­taken. To date, the 13,000 work-years devoted to these spacecraft are half as much as all the labor summoned by King Cheops of

Egypt to build the Great Pyramid at Giza, with its slanted passage­way so that the dead pharaoh’s soul could reside with the stars.25 Now, 4,500 years later, we have the means to go there directly as our robotic emissaries glide toward other worlds.

The centerpiece of Cassini’s symphonic mission, a brief aria of great excitement and beauty, was the descent of the Huygens probe to the surface of Titan in 2005.40 Titan is the most Earth-like world in the Solar System. It has weather, erosion, active geology, and a complex topography of lakes and rivers and flood plains. Three billion years ago, when the Sun was dimmer and no oxygen had been pumped into Earth’s atmosphere by microbes, the two cold worlds had strong similarities.

Huygens represented the main contribution of the European Space Agency to the Cassini mission and even though it returned a modest amount of data, it was not a disappointment. On Decem­ber 25, 2004, the probe separated from the main craft and began its perilous descent. Buffeted by winds in the upper atmosphere and unable to get a navigational lock on the Sun due to the thick smog, it slowed by parachute and landed on January 14, 2005, on what appeared to be a flood plain, scattered with cobbles of water ice (plate 8). Since the surface conditions of Titan were unknown, Huygens was never designed to be a lander. Rather, it was designed to survive landing on any surface from rocks to ocean, and trans­mit a small amount of data before expiring. This was dictated by the limitations of the batteries, which only had three hours of life, much of which was taken up by the descent. There was one minor disaster in the mission, when a software error prevented some of the lander’s images from being uploaded. While 350 images were returned, a similar number were lost. There was also a major di­saster averted. Long after launch, some dedicated and persistent engineers discovered that Cassini’s communication equipment had a major design flaw which would have caused the loss of all Huy­gens’s data. The probe had to send its data by radio to Cassini’s 4- meter antenna and then on to Earth. However, the acceleration of the probe would have Doppler-shifted its data out of range of the Cassini hardware, and the hardware could not be reprogrammed. To salvage this situation, flight engineers changed the landing and flyby trajectory so that the Doppler shift was greatly reduced.

Huygens weighed 700 pounds and carried six scientific instru­ments, most of which had been designed to study the atmosphere.

A microphone on one instrument captured the first sounds ever recorded on any planetary body apart from Earth. Another instru­ment mapped wind speeds at all elevations down to the ground. A third carried a lamp to illuminate the surface, which was useful, since Titan is a very murky moon. Huygens team member Martin Tomasko recalled: “We had great difficulty obtaining these pic­tures. We had only one percent of the illumination from the Sun, we’re going into a very thick atmosphere with lots of haze that blocks light from penetrating to low levels, and we’re taking pic­tures of an asphalt parking lot at dusk.”41 A fourth instrument did the clever trick of heating itself up just before the impact so it could analyze the vapor that came off the surface. The surface was a frigid -290°F or -179°C, cold enough that ice is brittle and methane is a liquid. Scientists clustered around monitors in the mission control room got to stare at a bleak and remarkable scene for several hours, longer than the expected thirty minutes, before the batteries finally died.

On a typical summer’s day in 2011, the current conditions at Space- weather. com read: “Solar Wind speed 515.9 kilometers per second, 0.3 protons per cubic centimeter.” That’s a speed of 1,125,000 mph and just one atom in the volume of a sugar cube, or a vacuum a bil­lion billion times thinner than the air we breathe. The website also predicts “X-Ray Solar Flare: 24-hr max: B4.” That’s a puny flare, thousands of times weaker than the 1859 event.9 In space weather rankings, B-class solar flares are completely “below the radar” and negligible, C-class X-ray solar flares are small and have very little impact on Earth, M-class flares cause momentary radio blackouts and can affect Earth’s Arctic and Antarctic regions, and X-class flares are major events causing planet-wide blackouts and week – long radiation storms. NOAA, the National Oceanic and Atmo­spheric Administration (more commonly known as the National Weather Service), provides detailed space weather reports updated every ten minutes. But what, one might ask, is the relevance of solar flares for our protected oasis of life on Earth, 93 million miles from the Sun?

Like a lonely sentinel stationed roughly a million miles from Earth at the Lagrangian point L1, NASA’s Solar and Heliospheric Observatory (SOHO) keeps a steady finger on the Sun’s pulse. Its game is called helioseismology, or the study of the “hum” of the sound waves reverberating throughout the Sun. Scientists use these acoustic probes to better understand its interior structure and energy production as well as possibly predict disturbances at the surface, like sunspots. SOHO has demonstrated with great clarity that solar flares—the sudden explosions of matter, electro­magnetic radiation, and high-energy particles from the Sun—can be unimaginably energetic cataclysms (plate 11). As University of Michigan Space Physics professor Mark Moldwin notes, “Flares release tremendous amounts of energy in a few minutes and can reach temperatures of 100 million K (much hotter than even the core of the Sun).”10 Space telescopes like SOHO and the new Solar Dynamics Observatory (SDO) are giving scientists a front row seat in observing the powerful dynamo of our star.

The Sun has magnetic poles. Approximately every eleven years, the direction of the poles reverses—imagine an object trillions of times bigger than a bar magnet completely reorienting its magnetic field. Such large-scale restructuring unleashes incredible magnetic forces, which lead over a few years to an exponentially greater degree of solar activity and solar storms. The tremendous ener­getic output at the most volatile stage of the process is known as the solar maximum. John Weiley’s IMAX film Solarmax (2000) has captivated audiences at planetaria and science museums with SOHO footage of the Sun’s violent storms leading up to the solar maximum of 2000 and 2001. The film’s amazing time-lapse foot­age demonstrates our Sun’s variability and the explosive energy of coronal mass ejections, plasma and magnetic fields blown off from the Sun’s corona that can cause severe magnetic storms on Earth.

The Earth’s magnetosphere largely protects us from the solar wind,11 the Sun’s outpouring of highly charged particles. More than that, this protection has been essential for the survival of life as we know it. Mars has a much weaker magnetic field and long ago lost most of its atmosphere and all of its oceans in large part due to the solar wind. However, when they reach dangerous levels, storms in space can cause power grid blackouts leaving millions without electricity, and may produce a rapid buildup of powerful electrical charges on satellites that can fry their delicate instru­ments. It has only been in the last few decades that we’ve realized the impact of space weather.

Space weather researchers highlight “evidence of the influence of solar activity on the terrestrial climate.”12 Mark Moldwin points out that in the 350-year span between AD 900 and 1250, during an extended warming period produced by increased solar activity, the North Atlantic experienced much milder temperatures. This prompted Nordic people to establish communities in Greenland and assign the region a “name that seems peculiar now since it is covered by one of the world’s largest ice sheets year round.”13 When solar activity subsequently decreased, Greenland froze over and settlers there either migrated or died. Later, during what is often called the Little Ice Age, lasting roughly between 1550 and 1750, historians report “winters were so cold. . . the principal riv­ers in mid-latitude Europe froze over.”14 This has been attributed to a solar minimum and apparently an extended period in which there were few sunspots.

The Earth naturally has gone through cycles of ice ages, but as Moldwin explains, the most recent, the Quaternary, extended from 2.5 million years ago to about 10,000 years ago, when large reaches of ice receded. The problem we’re currently facing is global warming, where temperatures consistent for the last 10,000 years are now on the rise. Moldwin writes, “Model predictions indicate that Earth’s climate will be drastically different than it is today in less than 100 years because of the burning of hydrocarbon fuel for transportation and energy. That is very quick compared to the nor­mal timescale of climate change.”15 Added to this is the fact that solar storms can seriously damage the Earth’s ozone layer, which protects all life on Earth from damaging ultraviolet rays and could, in turn, further contribute to warming Earth’s atmosphere.

NASA created its “Living with a Star” program in 2001 to gather better data for understanding the effects of the Sun on the Earth.16 If we ever move beyond our planet and engage in routine space exploration, we must leave the protective “bubble” provided by the Earth’s magnetic field and atmosphere. Our spaceships and astronauts will have to deal with the Sun and its stormy weather directly. A small armada of spacecraft has been involved in this ef­fort, but the most notable is a very sturdy device that’s still going strong seventeen years after its launch.

Space is mostly empty, but a thin gruel of gas and dust that occupies regions between stars dims and reddens light.1 Thousand-trillion- mile wide clouds containing gas and microscopic dust grains ab­sorb and attenuate visible light and reradiate it at infrared wave­lengths. NASA’s Spitzer Space Telescope has the remarkable ability to see through interstellar dust and has allowed us to look into the vast clouds in which stars are born, like those of the Orion Nebula, our nearest star-forming region. Spitzer can also peer into the dark, dust strewn plane of our Milky Way galaxy that previ­ously had been nearly impossible to penetrate. Anything that ra­diates heat, such as living bodies, and any cool object in space, such as planets or moons or even tiny silicate (rocky) and carbon (sooty) grains 1/10,000 to 1/100 of a millimeter across, emits in­frared radiation. Only an infrared telescope can image objects that glow in light waves too long for the human eye to see. The Spitzer Space Telescope can detect such light billions of light-years from Earth and has revealed this cool and invisible universe with un­precedented clarity.

With more than 850 exoplanets known as of early 2013, and another 2,700 candidate planets identified by the Kepler telescope, astronomers estimate that there are at least 50 billion exoplanets in the Milky Way galaxy. Scientists calculate that 500 million of those planets orbit in the habitable zone, the distance from their star that could allow for life.2 NASA’s Spitzer Space Telescope is helping to

detect and characterize these extrasolar worlds. In December 2010, Spitzer discovered the first carbon-rich exoplanet, named WASP- 12b, the geology of which may be comprised largely of diamond and graphite.3 Whereas rocks on Earth generally consist of silicon and oxygen in the form of quartz and feldspar, Spitzer’s observa­tions suggest that WASP-12b, about 1,200 light-years from here, has nothing like terrestrial geology. Astronomer Marc Kuchner of NASA Goddard Space Flight Center, who has helped theorize carbon-rich planets, explains that increased carbon in a planet’s composition can entirely alter its geology: “If something like this had happened on Earth, your expensive engagement ring would be made of glass, which would be rare, and the mountains would all be made of diamonds.”4 Spitzer has been instrumental in analyzing the geological makeup of exoplanets, and what astronomers are finding exceeds their wildest expectations.

At the other extreme from dim worlds in the nearby universe, Spitzer has discovered massive galaxies billions of light-years away that are forging stars at a prodigious rate. An infrared-bright, star­forming galaxy might be making thousands of stars each year compared to a couple for the Milky Way. These “starburst” galax­ies are infrared beacons from the early construction phase of the universe, during which many large galaxies were being assembled from smaller galaxy “pieces” for the first time.5 Deep within the dust-obscured hearts of distant galaxies, new worlds were being forged at a fantastic rate. A single, modest-sized telescope in space has seen directly into the center of these galaxies and provided insights on the full range of their creation stories.

As we saw in the last chapter, Mars seems dead to the orbiters that daily send back images of the surface. The atmosphere is tenuous, ultraviolet radiation and cosmic rays scorch the soil, and it rarely gets above freezing even on the balmiest summer day.15 It’s un­likely any form of life could exist on the surface now, but Mars has not always been so inhospitable. NASA’s strategy in searching for life in the Solar System is to “follow the water,” and even if there’s no surface water now, there was in the past. Each of the Mars Ex­ploration Rovers, Spirit and Opportunity, was designed for just a ninety-day mission. In the end, they have vastly exceeded expecta­tions with their indomitable traverses of the forbidding Martian terrain. Think of them as twin robotic field geologists whose pri­mary goal is to search for the signposts of water.16 The record of past water can be found in the rocks, minerals, and landforms on Mars, particularly those that could only have formed in the pres­ence of water.

Spirit and Opportunity were not designed to detect current or past life in the Martian soil,17 but they can do the detective work needed to say whether there have been stable bodies of water that could have supported life in the past. Surface rocks reveal evidence of previous water in the way that they formed, by processes like precipitation, evaporation, and sedimentation. They can also hold clues for the possibility that water currently exists under the sur­face. The rovers have helped scientists diagnose the history of the Martian climate, which is now thought to have been warmer and wetter 2-3 billion years ago. The twin robots are also trying to parse the different contributions of wind, water, plate tectonics, volcanism, and cratering to the sculpting of the surface. Spirit and Opportunity provide “ground truth” data for calibrating the or – biters that continue to do remote geology and scout for future landing sites. A final goal is to prepare the stage for future as­tronauts by understanding the unique challenges of the Martian environment.

Chesley Bonestell’s lifelike paintings of Saturn as seen from the surface of Titan and other moons, published in 1944 in LIFE magazine, sparked the public imagination regarding the kind of geographies we would someday find in the outer Solar System. In characterizing the large gas planets and their moons, Voyager con­firmed what astronomers had long suspected: the Earth to some degree serves as an analog for meteorological and geological pro­cesses on other worlds. Serge Brunier explains, “Fogs, clouds, gla­ciation, the cycle of the seasons, aerial erosion, and volcanism are universal phenomena.”26 But the geological processes occurring on worlds billions of miles from the Sun both surprised and mes­merized scientists and space enthusiasts across the globe. Close-up views of Jupiter’s moons indicated internal heating as they flex in the tides of their host planet’s gravity. A probable ocean of water captured under the fractured and icy surface of Europa, and Ti­tan’s seas of liquid methane, both suggested strange and captivat­ing geographies.

Planet encounters garnered global attention and were keenly covered by the press. When Voyager 1 arrived at Saturn in Novem­ber 1980, Henry Dethloff and Ronald Schorn report that approxi­mately 100 million people tuned in to live television broadcasts from NASA’s Jet Propulsion Laboratory while roughly five hundred reporters from across the globe provided news coverage “unprec­edented in the history of unmanned space exploration.”27 It’s no wonder public interest in the mission was so intense. Voyager liter­ally beamed into our living rooms footage of worlds being charted for the first time. Of Voyager 1’s encounter with the second larg­est planet in our Solar System, former JPL Director Bruce Murray writes: “Both Time and Newsweek ran Saturn cover stories. Live

programming flowed daily from Pasadena to a network of view­ers in countries ranging from Canada to Finland and, especially, Japan. Colorful images of Saturn surrounded by its magnificent rings rapidly became pop art cultural symbols.” Saturn’s weather turned out to be wilder than Jupiter’s. A layer 1,200 miles thick has winds of over 1,000 mph. Murray recalls that President Jimmy Carter, curious about wind speeds and whether auroras had been detected on Saturn, phoned to say: “The Saturn pictures are fan­tastic. I watched two hours yesterday as well. Didn’t expect to have so much time available.” In the summer of 1989, when Voyager 2 arrived at Neptune and its moon Titan, black and white still im­ages were broadcast live as they streamed from the spacecraft, and NASA, PBS, and CNN arranged for live reports at regular intervals throughout the encounter. Voyager’s televised encounters allowed scientists and general audiences opportunity to ramble “through a cosmic Louvre,” writes Murray. “For the millions viewing PBS’s ‘Jupiter Watch’ telecasts, ABC’s ‘Nightline’ programs, or Carl Sa­gan’s ‘Cosmos’ series or watching the images appearing on screens in Japan, England, Mexico, and South America, Voyager revealed a treasure trove of abstract art.”28

Carl Sagan was a member of Voyager’s imaging science team and he incorporated into his PBS TV program Cosmos (1980) ani­mations of planetary flybys and computer-generated graphics pro­duced at JPL by the Voyager team.29 Through the PBS series, his book of the same title, and late night talks with Johnny Carson, Sagan worked to capture and generate widespread public interest in planetary science and the Voyager mission. A celebrated senior astronomer at Cornell University, Sagan dedicated his life to popu­larizing the latest findings in astronomy and planetary science, at a time when most astronomers were unwilling to risk their schol­arly reputations to do so. He fed a fascinated public exactly what they hoped for and wanted. Having researched the atmosphere of Venus as an example of runaway greenhouse effects, Sagan championed NASA’s projects and delighted in articulating in de­scriptive imagery astronomical and planetary phenomena. It was Sagan who suggested that Voyager, once beyond the orbit of Nep­tune and receding from the ecliptic plane, should capture a pho­tograph of Earth as it really appears in the scale of the Solar Sys­tem—a seemingly unimpressive “pale blue dot” as he evocatively named it.

Before Cassini arrived at Saturn, astronomers had paid little atten­tion to Enceladus, a moon one-tenth the size of Titan. The Voyag­ers had shown in the 1970s that Enceladus was like an icy billiard ball, reflecting almost 100 percent of the Sun’s light. Its surface gave indications of activity since some parts were old and heavily cratered while others seemed to have been altered by volcanism in the last hundred million years. But nothing in earlier data prepared scientists for what Cassini would reveal.

In 2005, plumes were seen rising from the fractured, icy surface (figure 5.5). It took several years and numerous observations by Cassini’s instruments to build up a picture of what was going on, but this is what we know. Enceladus emits geysers of tiny ice par­ticles from a number of hot spots on its surface, near the southern polar region. The plumes are ejected at over 1,000 mph, greater than the escape velocity. They rise thousands of miles above the surface and form Saturn’s E ring.42 The geysers arise from geologi­cal features called “tiger stripes” that are 100-200°F warmer than

other areas of the moon. Geologists think there’s spreading and tectonic activity in the tiger stripes, similar to what happens near deep-sea ocean ridges on Earth. Tidal heating must play a role, but the cause of the active geology on Enceladus is still a mystery, since the neighboring and similarly sized moon Mimas is inactive. Cas­sini has swooped through the plumes on several occasions, three times approaching the moon within 30 miles, “tasting” the mate­rial with its instruments to determine the chemical composition. The plumes are made of tiny ice particles and vapor that includes methane, ethane, propane, acetylene, and other organic molecules. The chemical composition may be like a comet. Most excitingly, the plumes contain sodium chloride—common salt. That’s the best indication so far that Enceladus has a subsurface ocean that oc­casionally erupts through the surface.

Much of this information was gathered in a series of swooping flybys, the closest of which zoomed within 15 miles of the surface. The imaging team calls these maneuvers “skeet shoots.” The space­craft is moving so fast and is so close to the moon that the camera can’t track or lock onto any particular geological feature. Some images resolve features as small as 10 meters across, about the size of a living room. In late November 2009, Cassini made its eighth flyby of the tiny moon, the last before Enceladus entered the shad­ows of the long, cold Saturnian winter. With no new mission slated to return to the outer Solar System for at least fifteen years, it will be a while before we see images like this again. Meanwhile, the presence of liquids on Titan and inside Enceladus naturally leads to speculations about biology. Our dreams turn to the possibility of creatures floating in the dark and frigid depths of lunar seas far from their sheltering stars.