An intimate history of Earth and the quest for life beyond the solar system
For 4.6 billion years our living planet has been alone in a vast and silent universe. But soon, Earth's isolation could come to an end. Over the past two decades, astronomers have discovered thousands of planets orbiting other stars. Some of these exoplanets may be mirror images of our own world. And more are being found all the time.
Yet as the pace of discovery quickens, an answer to the universe's greatest riddle still remains just out of reach: Is the great silence and emptiness of the cosmos a sign that we and our world are somehow singular, special, and profoundly alone, or does it just mean that we’re looking for life in all the wrong places? As star-gazing scientists come closer to learning the truth, their insights are proving ever more crucial to understanding life’s intricate mysteries and possibilities right here on Earth.
Science journalist Lee Billings explores the past and future of the "exoplanet boom" through in-depth reporting and interviews with the astronomers and
planetary scientists at its forefront. He recounts the stories behind their world-changing discoveries and captures the pivotal moments that drove them forward in their historic search for the first habitable planets beyond our solar system. Billings brings readers close to a wide range of fascinating characters, such as:
FRANK DRAKE, a pioneer who has used the world’s greatest radio telescopes to conduct the first searches for extraterrestrial intelligence and to transmit a message to the stars so powerful that it briefly outshone our Sun.
JIM KASTING, a mild-mannered former NASA scientist whose research into the Earth’s atmosphere and climate reveals the deepest foundations of life on our planet, foretells the end of life on Earth in the distant future, and guides the planet hunters in their search for alien life.
SARA SEAGER, a visionary and iron-willed MIT professor who dreams of escaping the solar system and building the giant space telescopes required to discover and study life-bearing planets around hundreds of the Sun’s neighboring stars.
Through these and other captivating tales, Billings traces the triumphs, tragedies, and betrayals of the extraordinary men and women seeking life among the stars. In spite of insufficient funding, clashing opinions, and the failings of some of our world’s most prominent and powerful scientific organizations, these planet hunters will not rest until they find the meaning of life in the infinite depths of space. Billings emphasizes that the heroic quest for other Earth-like planets is not only a scientific pursuit, but also a reflection of our own culture’s timeless hopes and fears.
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Lee Billings is a science journalist whose work has appeared in Nature, New Scientist, Popular Mechanics, and Scientific American. He lives in New York. This is his first book.Excerpt. © Reprinted by permission. All rights reserved.:
Here on Earth we live on a planet that is in orbit around the Sun. The Sun itself is a star that is on fire and will someday burn up, leaving our solar system uninhabitable. Therefore we must build a bridge to the stars, because as far as we know, we are the only sentient creatures in the entire universe. . . . We must not fail in this obligation we have to keep alive the only meaningful life we know of.
–WERNHER VON BRAUN,
ARCHITECT OF NASA’S APOLLO PROGRAM,
AS RECALLED BY TOM WOLFE
This story properly begins 4.6 billion years ago, with the birth of our solar system from a cloud of cold hydrogen and dust several light-years wide. The cloud was but a wisp from a much larger mass of primordial gas, a stellar nursery manufacturing massive stars destined to explode as supernovae. One by one, the giant stars popped off like firecrackers, ejecting heavy elements that sizzled with radioactivity as they rode shock waves through the murk like so much scattered confetti. One of those enriching shock waves may have compressed the cloud, our cloud, in its passage. The cloud became dense enough for gravity to seize control, and it collapsed in on itself. Most of its material fell to its center to form a hot, simmering protostar. Eventually, the protostar gained enough mass to kindle a thermonuclear fire at its core, and the Sun began to shine. What was left of the cloud settled around the newborn star in a turbulent, spinning disk of incandescent vapor.
Microscopic grains of metal, rock, ice, and tar rained out from the whirling disk as it slowly cooled. The grains swirled through the disk for millennia, occasionally colliding, sometimes sticking together, gradually glomming into ever-larger objects. First came millimeter-scale beads, then centimeter-scale pebbles, then meter-scale boulders, and finally kilometer-scale orbiting mountains called “planetesimals.” The planetesimals continued to collide, forming larger masses of ice, rock, and metal that grew with each impact. Within a million years, the planetesimals had grown into hundreds of Moon-size embryos, protoplanets that through violent collisions grew larger still, until they became full-fledged worlds.
After perhaps one hundred million years of further collisions, the embryos in the inner solar system had combined to make Earth and the other rocky planets. The inner worlds were likely bone-dry, their water and other volatiles blowtorched away by the intense light of the newborn Sun. In the outer solar system, freezing temperatures locked the volatiles in ice. The ices provided more-solid construction material, allowing the cores of Jupiter and the other outer planets to rapidly form and sweep up lingering gas within the disk in only a few million years. As they grew, the giant planets created zones of instability where embryos could not assemble, leaving behind pockets of primordial planetesimals and bands of shattered rock and metal. These remnants are the asteroids. The giant planets also catapulted many icy planetesimals far out into the solar hinterlands, to drift in the dark out beyond the orbit of present-day Pluto. When jostled by perturbing planets, galactic tides, or close-passing stars, those icy outcasts fall back toward the Sun as comets.
Finally, sometime between 3.8 and 4 billion years ago, a complex, chaotic, hazily understood series of gravitational interactions between the giant planets stirred up most of the outer solar system, sending barrages of asteroids and comets hurtling sunward to pound the dry, rocky inner worlds. This event is called the “Late Heavy Bombardment,” and was the last gasp of planet formation. We observe its effects in the cratered surface of the Moon, and also in the rain that has eroded its geographic scars from our own planet—much of Earth’s water seems to have arrived during the Bombardment, express-delivered from the outer solar system. Afterward, Earth’s crust had partially melted, and its original atmosphere had been mostly swept away. But as those first torrential rains fell from the steam-filled sky, our planet gained the gift of oceans. Slowly, the Earth cooled, and gas-belching volcanoes gradually replenished the atmosphere. Soon, perhaps uniquely of all the new-formed worlds of the solar system, ours would somehow come alive.
Slightly less than four billion years later, I was four years old, standing with my mother, father, and sister in our backyard in Jasper, Alabama. It was January 1986, shortly after sunset. My father had built a small bonfire, and we clustered around it against the evening chill, roasting marshmallows as the stars came out overhead. Lower in the sky, just above the treetops, a soft white smear was barely visible. It was Halley’s comet, passing near Earth on its trip around the Sun. I remember asking whether I could visit it. I had recently seen the 1974 film adaptation of Saint-Exupéry’s The Little Prince, and, like the small boy living on an asteroid in the story, I, too, wanted to fly through space to see all the solar system’s strange places. “Maybe someday,” the answer came. Weeks later, I and the rest of a generation of children would learn that space travel is no fairy tale, watching as NASA’s space shuttle Challenger broke apart on its way to orbit.
I didn’t know then that Halley’s comet would not be coming back until far-off 2061, and I was much too young to feel the weight of that date. The comet didn’t feel it, either—when it returned, it would be practically unchanged. I, on the other hand, would be nearing my eightieth year on Earth, if I was so lucky. With a great deal more luck, my parents would see it through centenarian eyes.
When I was ten, after we had moved to Greenville, South Carolina, my mother spent much of one summer teaching illiterate adults to read at a local library. She always brought me along, letting me wander the shelves unsupervised. I began reading enormous amounts of science fiction about alien civilizations and interstellar travel, as well as books about astronomy, which tended to gloss over the possibility of planets and lives beyond our solar system in favor of bigger, flashier things—exploding suns, colliding galaxies, voracious black holes, and the Big Bang. Such was the spirit of the times: for most of the twentieth century, astronomers had been all-consumed by a quest to gaze ever deeper out into space and time, pursuing the fundamental origins and future of existence itself. That quest had revealed one revolutionary insight after another, showing that we lived in but one of innumerable galaxies, each populated by hundreds of billions of stars, all in an expanding universe that began nearly fourteen billion years ago and that might endure eternally. I thrilled at the cosmological creation story but couldn’t help but think that it was missing something. Namely, us. Lost somewhere in between the universe’s dawn and destiny, a ball of metal, rock, and water called Earth had given birth not only to life, but to sentient beings, creatures with the intellectual capacity to discover their genesis and the technological capability to design their fate. Creatures that, before their sun went dim, might somehow touch the stars. Maybe what had happened once would happen many times, in many places. My father saw the galaxies and stars on the covers of my checked-out library books and bought me a department-store telescope.
Looking through my telescope, I was soon disappointed to learn I couldn’t see many of the cosmic fireworks described in the astronomy books, or any evidence for the galactic empires of science fiction. Everything out there looked awfully, deathly quiet. It seemed in all that cosmic space, and thus in the great minds of many learned astronomers, there was paradoxically no room for living beings and their tiny home worlds. Such things were too small to be searched for, too insignificant to be of notice. I kept looking every now and then anyway, half-hoping I might catch a UFO in my viewfinder as it streaked across the sky, or see the bright flashes of some interstellar battle in the twinkling of a star. One day I asked my father whether any planets at all existed around other stars. He thought a moment, and replied that other stars probably had planets, but that no one really knew; none had ever been found, because they were all so far away. After that, most times when I gazed up at the night sky, I would wonder what those planets might look like. Would they be like Earth? Would they have oceans and mountains, coral reefs and grasslands? Would they have cities and farms, computers and radios, telescopes and starships? Would creatures there live and die as we did, or look up and wonder about life’s purpose? Would they be lonely? Staring at the trembling stars, I dreamed of worlds I thought I would never see.
By the mid-2000s, I had followed my curiosity into a career in science journalism, where instead of pestering personal friends and acquaintances with my questions, I could simply pester the experts themselves. Answers to some of my earlier questions had emerged over the intervening years: planets proved quite common around other stars, and since the mid-1990s astronomers had found hundreds of them. These worlds were called “exoplanets,” and most were far too large and far too near their suns to be hospitable to life as we know it. Using large telescopes on the ground and in space, astronomers had even managed to take pictures of a few that were very hot, very big, and relatively nearby. But other questions remained unaddressed: Were there other Earth-size, Earth-like exoplanets in our galaxy and in the wider universe? Was our situation here on Earth average, or was it instead quite special, even unique? Were we cosmically alone? I decided to write this book when I learned just how soon we might gain answers to some of these seemingly timeless questions.
It was 2007, and I was interviewing the University of California, Santa Cruz, astrophysicist Greg Laughlin for a story. During our chat, Laughlin explained that since exoplanet searches were becoming progressively more sophisticated and capable, there would soon be thousands rather than hundreds of known exoplanets to compare with our own. Astronomy’s next big thing, he suggested, would focus not on the edges of space and the beginning of time, but on the nearest stars and the uncharted, potentially habitable worlds they likely harbored. Near the end of our conversation, he guessed that the first Earth-size exoplanets would probably be found within the next five years. He had graphed the year-to-year records for lowest-mass exoplanets, drawing a trend line through the data that suggested an Earth-mass planet would be discovered in mid-2011. It suddenly seemed I had stumbled upon some magnificent secret, hidden in plain view. The more exoplanet-related press releases and papers I read, the more convinced I became that somewhere on Earth there were scientists who would be remembered in history for discovering the first habitable worlds beyond the solar system, and perhaps even the first evidence of extraterrestrial life. Yet they were largely anonymous, utterly unknown to the average person. I wanted to learn more about them, and tell their stories. One by one, I sought them out.
Most welcomed me with open arms, and the ones who didn’t still politely tolerated me. Many planned for a bright near-future, one in which they would use great, government-built techno-cathedrals of glass and steel on remote mountaintops and in deep space to wring secrets from the heavens and investigate any promising exoplanets for signs of life. Looking further out in time, some even envisioned our culture eventually escaping Earth entirely to expand into the wider solar system and beyond, driven by a curiosity so insatiable and restless that it would forever propel us outward into the endless immensities of new, far-flung physical frontiers. And yet, as I researched the book, I saw many of their boldest hopes dashed as crucial telescopes and missions were delayed or canceled, deferring all those dreams for generations, if not forever. On the verge of epochal revelations, their work had faltered, but not because of any newfound limitations of celestial physics. Instead, rapid progress in the search for life beyond Earth had succumbed to purely human, mundane failings—negligent organizational stewardship, unsteady and insufficient funding, and petty territorial bickering. Time and time again I felt I was witnessing the planet hunters reach for the stars just as the sky began to fall. And so I became committed to telling not only their personal stories, but also the story of their field, where it came from and where, with a reversal of fortune, it might still go.
The result is the book you now hold in your hands. By necessity, it glosses over or fails to mention numerous discoveries and discoverers that deserve entire shelves of dedicated literature. I hope the knowledgeable reader will forgive my omissions in light of all that this work does encompass. It is a portrait of our planet, revealing how the Earth came to life and how, someday, it will die. It is also a chronicle of an unfolding scientific revolution, zooming in on the ardent search for other Earths around other stars. Most of all, however, it is a meditation on humanity’s uncertain legacy.
This book’s title, Five Billion Years of Solitude, refers to the longevity of life on Earth. Life on this planet has an expiration date, if for no other reason than that someday the Sun will cease to shine. Life emerged here shortly after the planet itself formed some four and a half billion years ago, and current estimates suggest our world has a good half billion years left until its present biosphere of diverse, complex multicellular life begins an irreversible slide back to microbial simplicity. In all this time, Earth has produced no other beings quite like us, nothing else that so firmly holds the fate of the planet in its hands and possesses the power to shape nature to its whim. We have learned to break free of Earth’s gravitational chains, just as our ancient ancestors learned to leave the sea. We’ve built machines to journey to the Moon, travel the breadth of the solar system, or gaze to the edge of creation. We’ve built others that can gradually cook the planet with greenhouse gases, or rapidly scorch it with thermonuclear fire, bringing a premature end to the world as we know it. There is no guarantee we will use our powers to save ourselves or our slowly dying world and little hope that, if we fail, the Earth could rekindle some new technological civilization in our wake of devastation.
In the long view, then, we are faced with a choice, a choice of life or death, a choice that transcends science to touch realms of the spiritual. As precious as the Earth is, we can either embrace its solitude and the oblivion that waits at world’s end, or pursue salvation beyond this planetary cradle, somewhere far away above the sky. In our lives we all in some way contribute to this greater choice, either drawing our collective future down to Earth or thrusting it out closer to the stars. Some of the people in this book have devoted themselves to seeking signs of other, wildly advanced galactic cultures, hoping to glimpse our own possible futures via interstellar messages carried on wisps ...
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