Are we alone in the universe? Almost certainly not. In First Contact, Marc Kaufman provides a gripping tour of the magnificent new science of astrobiology that is closing in on the discovery of extraterrestrial life. In recent decades, scientists generally held that the genesis of life was unique to Earth: It was too delicate a process, and the conditions needed to support it too fragile, for it to exist anywhere else. But we are now on the verge of the biggest discovery since Copernicus and Galileo told us that Earth is not at the center of the universe. New scientific breakthroughs have revolutionized our assumptions about the building blocks of life and where it may be found. Scientists have hunted down and identified exoplanets, those mysterious balls in the universe that orbit distant suns not too different from our own. They have discovered extremophiles, the extraordinary microbes that thrive in environments of intense heat or cold that may mimic the inhospitable conditions of other planets. They have landed rovers on Mars and detected its methane, a possible signature of past life. And they have created sophisticated equipment to sweep the sky for distant radio signals and to explore the deep icebound lakes of Antarctica. Each of these developments has brought forth a new generation of out-of-the-box researchers, adventurers, and thinkers who are each part Carl Sagan, part Indiana Jones, part Watson and Crickand part forensic specialists on CSI: Mars. In this masterful book, Kaufman takes us to the frontiers of astrobiology's quest for extraterrestrial life and shows how this quest is inextricably linked with the quest to understand life on Earth. He takes us deep under the glaciers of Antarctica, into the mouth of an Alaskan volcano, and beneath the Earth into the unbearable heat of a South African mine, and leads us to the world's driest desert. For thousands of years, humans have wondered about who and what might be living beyond the confines of our planet. First Contact transports us into the cosmos to bring those musings back to Earth and recast our humanity.

Marc Kaufman is a science writer and former national editor for The Washington Post. He lives outside of Washington, D.C. Visit him at www.habitablezones.com.

The Biggest Discovery of Them All	p. 1
Really Extreme Life	p. 15
What Makes Something Alive?	p. 35
The Spark of Life	p. 59
On The Trail of Life on Mars	p. 79
Three Eurekas on Hold	p. 105
Planet-Hunting	p. 127
Life and the Laws of Physics	p. 149
Far-Flung Intelligent Worlds	p. 161
The Day After First Contact	p. 179
Acknowledgments	p. 191
Note On Sources	p. 195
Bibliography	p. 201
Index	p. 207
Table of Contents provided by Ingram. All Rights Reserved.

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1 THE BIGGEST DISCOVERY OF THEM ALL

If it’s just us in this universe, what a terrible waste of space.

But it’s not. Before the end of this century, and perhaps much sooner than that, scientists will determine that life exists elsewhere in the universe. This book is about how they’re going to get there. And when they do, that discovery will rival the immensity of those that launched our previous scientific revolutions and, in the process, defined our humanity. Copernicus and Galileo told us we were not, after all, at the center of the universe, and their ideas fathered a scientific astronomy that, four hundred years later, is allowing us to be a space-faring planet. Charles Darwin gave us our evolutionary roots, which, a century later, propelled Louis and Mary Leakey on a thirty-year search culminating in the recovery of fossil hominid remains almost two million years old in Tanzania’s Olduvai Gorge—proof that humankind began in Africa. So here we are now, the descendants of the skilled toolmakers and explorers who left the continent some sixty to seventy thousand years ago. We’ve populated the globe and sent astronauts to the moon. Next up: Life beyond Earth.

For thousands of years, humans have wondered about who and what might be living beyond the confines of our planet: gods, beneficent or angry, a heaven full of sinners long forgiven, creatures as large and strange as our imagination. Scientists now are on the cusp of bringing those musings back to Earth and recasting our humanity yet again. “Astrobiology” is the name of their young but fast-growing field, which immodestly seeks to identify life throughout the universe, partly by determining how it began on our planet. The men and women of astrobiology—an iconoclastic lot, quite unlike the caricatures of geeks in white lab coats or UFO-crazed conspiracy theorists—are driven by a confidence that extraterrestrial creatures are there to be found, if only we learn how to find them. Most hold the conviction that if a form of independently evolved life, even the tiniest microbe, is detected below the surface of Mars or Europa, or other moons of Jupiter or Saturn, then the odds that life does exist elsewhere in our galaxy and potentially in billions of others shoot up dramatically. A solar system that produces one genesis—ours—might be an anomaly. A single solar system that produces two or more geneses tells us that life can begin and evolve whenever and wherever conditions allow, and that extraterrestrial life may well be an intergalactic commonplace.

With goals so enormous and compelling, astrobiology has brought forth a new generation of outside-the-box researchers, field scientists, adventurers, and thinkers—part Carl Sagan, part Indiana Jones, part Watson and Crick, part CSI: Mars. They are men and women who drop deep below the surface of the Earth or tunnel into Antarctic glaciers in search of life in the most extreme places, who probe volcanoes for clues into how Earthly life began, who propel life-detecting robots and ultimately themselves into space. They come up with ever more ingenious methods for detecting planets that circle distant suns; they scour our planet for Mars- or Europa-like habitats they can minutely study for the life-supporting conditions they might encounter when our spaceships arrive there. They probe the cosmos as far as 13 billion light-years away for signs of the earliest stirrings of the order and chemistry that created life on Earth. Some are even working to define and understand “life” by creating it in the lab. They’ve harnessed that childhood excitement so many of us felt when, on hot, hard-to-sleep summer nights, we tried to imagine what it would be like to visit Mars (very dry), or travel to the end of the universe (very confusing), be around when life first began (very lonely), or come across extraterrestrial life (very exciting). The world has changed enough that today, a large and growing number of scientists are earning their livelihoods turning their imaginings into hypotheses and putting them to tests inconceivable even a decade ago.

Why now? Why does the promise of cracking the extraterrestrial barrier seem close enough that so many prominent scientists from NASA to the Massachusetts Institute of Technology, from the Carnegie Institution of Washington to Princeton and Cambridge universities, have decided to ignore the giggle factor associated with UFOs and ET and join the quest? The answer, put broadly, is that the field is getting results.

In the past ten years we have found that hundreds of planets orbit distant suns not too different from our own and can reasonably infer that billions more exist. Many are bound to be rocky planets in eminently habitable zones the right distance from stable suns to give life a chance. More than five hundred of these exoplanets (“exo” because they orbit suns other than our own) have already been identified and even more new ones are being discovered every week. In the past two decades, we have also explored a vast world of microbial “extremophiles” that live in Earthly environments once assumed to be incapable of supporting life—findings that make it easier to hypothesize that life survives in “uninhabitable” conditions on other planets and moons, too.

Extremophile research started with microbes living in hot springs like Yellowstone and near deep underseas “black smoker” thermal vents that are even hotter. Each year scientists reach further and almost always get results—finding life miles underground, encased in ice, or bathed in acid. A very different group of researchers is also getting closer to synthesizing something akin to life in the lab, research that sets the stage for an understanding of how life might have started on Earth and elsewhere. One of those labs will soon have produced self-replicating genetic material out of nonliving component parts—in other words, created something very life-like from synthesized genetic material. And planetary scientists are finding ever more reason to conclude that Mars in particular—written off as lifeless thirty years ago, after NASA’s Viking missions—has, or had in the past, most everything necessary to support life: liquid water, carbon compounds, nutrients, and a minimally protective atmosphere. In 2009, the life-on-Mars theory got a major boost with the confirmed discovery of methane gas in its atmosphere. On Earth, 90 percent of methane is produced through biology.

The field of astrobiology in its modern form came into existence in the late 1990s, following an announcement by NASA that its researchers had found likely signatures of life in an ancient Martian meteorite that landed in Antarctica. The proof supporting that conclusion was contested by many scientists, but the study of meteorites from Mars and elsewhere has blossomed anyway. Since then, increasingly sophisticated instruments have allowed researchers to tease more widely accepted secrets from the rocks. All these very concrete discoveries—and the fact that interstellar space is full of potentially life-supporting, carbon-based compounds that constantly rain down on us and on other celestial bodies—have convinced scientists around the world that it’s highly unlikely that Earth is the only place in the universe where life arose.

This is heady stuff, and it has scientists moving in all directions. If primitive life forms can exist miles below the Earth’s surface in the mines of South Africa without contact with the sun or its products, why couldn’t the same be true on Mars, or on the moons of Jupiter and Saturn, or on the untold number of rocky planets we now know exist across the universe? The same logic applies to extremophiles in the abyss of the deep sea, in glaciers tens of thousands of years old, in Spain’s acidic Rio Tinto or California’s alkaline and arsenic-laced Mono Lake. Extremophiles even survive in the upper atmosphere of our planet.

Perhaps you’re thinking that the discovery of bacteria deep underground does not seem all that earth-shattering. Perhaps you’re thinking, too, that even if Mars or a moon in our solar system turns out to have comparable subterranean life, that would prove little except that primitive life forms come into being and survive in all kinds of places. Astrobiologists see things very differently. As they are quick to point out, life has existed on Earth for at least 3.8 billion years, and for more than 3 billion of those years single-celled bacteria and related microbes were the only living things around. In other words, butterflies, tree sloths, saber-toothed tigers, and humans all evolved from single-celled organisms too small to see without a microscope. Astrobiologists today have a deep respect for the significance of bacteria and other single-celled creatures—and their ability to evolve into intelligent life.

Searching for and understanding extremophiles is almost universally embraced by the scientific community as essential and revelatory science now, but as late as the mid-1990s it was seen as quixotic and something of a career ender. Tullis Onstott is the man who changed the field by descending into deep gold mines in South Africa and coming back with remains of bacteria that have lived down there in their own peculiar worlds for millions of years. Onstott, a geobiologist at Princeton University, initially couldn’t get funding for his research, and his first expeditions were paid for out of his own pocket.

Stories like his are common in astrobiology. The early extrasolar planet hunters were told in the 1980s and early 1990s that they were wasting their time, that there was no way to detect their quarry through the blinding glare of parent stars hundreds or thousands of light-years away. So they developed other techniques based on measuring the slightest movements of those suns, minuscule course corrections caused by the gravity of the orbiting exoplanets. Now, through those methods, planets beyond our solar system are found regularly and the expectation is that billions more remain to be mapped. What we know of them remains limited to their orbits, their mass, and a little about their component parts. The new challenge is to characterize them much better, especially the smaller Earthlike planets expected to be discovered in the years ahead. But these planets are minute at such great distances and are blotted out by the intense light from their parent stars.

So how can astronomers compensate? One proposal, years in the making, involves sending into deep space a football-field-sized sunshade, that would then work in tandem with an orbiting telescope 35,000 to 50,000 miles away to create an “occulter.” The flower-petal-shaped screen would block light from the star and thereby allow the telescope to see and study orbiting planets, their atmospheres, and any signatures of possible life. The long process of transforming an idea like this into a space-faring reality got a big boost in 2010 when a panel of the National Academy of Sciences gave its highest priority to exploring exoplanets and their atmospheres in the next decade. An occulter system may ultimately not be the technology selected for the job, but it is a serious contender.

The sunshade might sound like a far-fetched project to pursue, but many of the most successful results in astrobiology began as pursuits that sounded impractical or extreme. Take, for instance, the work of Sara Seager, the astrophysicist who first opened my eyes to the breakthroughs and great promise of astrobiology. Her mind easily visits places where few of us can follow. Raised in Toronto, she puzzled her father with an early interest in outer space, which later turned into degrees in math, physics, and astronomy. Her pioneering work on the atmospheres of exoplanets is what persuaded MIT to offer her tenure and an endowed chair in planetary science. She was thirty-four at the time. She is a theorist rather than a hands-on planet hunter: her scientific specialty is to predict and refine ways to identify the elements and compounds in the atmospheres of extrasolar planets, work that she began before the first extrasolar planet was detected. She was told when she started that her ideas were theoretically interesting but couldn’t be tested in her lifetime. But little more than a decade later, we know that the gas methane exists on a giant planet orbiting a star 63 light-years away, that sodium exists on a planet orbiting a sunlike star 150 light-years away, and that evidence of both oxygen and carbon has been detected enveloping another planet in that solar system. Now Seager is convinced that extraterrestrial life will be detected within her lifetime, and she wants to be part of that triumph.

Given the size of the challenges taken on by astrobiology, however, the big break won’t come from the inspired minds of one or two great thinkers, as they did with Galileo, Copernicus, Newton, Darwin, Einstein, and Watson and Crick. This search is more of a broad-based, inexorable, but oddly unheralded Apollo program, an undertaking that requires thousands of researchers with very different backgrounds, technical skills, and obsessions. The enterprise is playing out in plain view, yet is so big it is almost invisible.

Some astrobiologists (and astrobiology fans) no doubt dream of a “Eureka!” moment when life is discovered beyond Earth or synthesized here—an equivalent to Neil Armstrong’s giant step on the moon, or the unraveling of the structure of DNA. Someday that may come, but science generally works incrementally, and takes much smaller bites. Even the biggest, hottest research questions in astrobiology involve work akin to crime-scene forensics, often drawing on small left-behind clues to help put together pieces of the larger puzzle. These are the kinds of questions absorbing, inspiring, and at times dividing the inherently fractious tribe that constitutes the field of astrobiology.

That tribe is fractious because it’s attempting to answer a set of unavoidable and obnoxious questions—obnoxious because they appear so simple, yet actually are so complex: What, when all is said and done, is life? Could we encounter it elsewhere and simply pass it by? Are we blinded to extraterrestrial life by our Earth-based assumptions of what life must be? We have a substance on Earth—a blackish rock coating called desert varnish found in many arid places and often used as a background for Native American petroglyphs. Experts in the field going back to Charles Darwin have studied it, and they still sharply disagree about where it comes from: whether it is a product of microbial biology or of geology and chemistry. Getting a better sense of what is living and what is not on Earth seems pretty essential to the quest for life beyond Earth, and so these borderland cases attract lots of attention. Desert varnish is especially intriguing because something that looks similar to it has been seen during several Mars missions, or so some scientists contend.

Nobody knows how or why, but virtually all the amino acids—molecules that make up essential building blocks of proteins (and therefore of life as we know it)—share a necessary quality that is otherwise seldom seen on Earth: Their molecules are all organized in a formation that scientists call “left-handed,” enabling them to interact with uniformly “right-handed” sugars. Because virtually nothing else on Earth is structured like this—all “left-handed” or all “right-handed”—some scientists suspect the initial overabundance of left-handed amino acids arrived here by way of meteorites or comet dust. Evidence from one large and quickly recovered meteorite that fell in Australia in 1969 lends some support to that conclusion, with potentially major implications about how life began and evolved here, and the possible makings of life elsewhere.

Did life on Earth start in scalding, sulfurous hydrothermal vents on the deep ocean floor, or perhaps at the less intense side vents that tend to spring up in the same regions? Did it start in subterranean rock fractures where it could be protected from the heavy meteor bombardment of early Earth? Did it begin around the plumes of erupting volcanoes, where intense lightning activity (the kind of energy needed to start the chemistry needed to support life) is now known to be common? Or did it begin in the “little warm ponds” put forward by Charles Darwin, or perhaps via those meteorites? All of these possibilities have their advocates. If scientists can get a clear sense of how nonliving chemicals were transformed into the self-replicating, energy-consuming, evolving entities that ultimately produced us here, they’ll have the beginning of a road map for what might be happening out there.

While this search is under way, another hunt for signs of extraterrestrial life—a broad range of potential “biosignatures” ranging from the presence of liquid water to the organic molecules associated with life on Earth—is also moving quickly ahead. For instance, the methane gas recently detected in the atmosphere of Mars is released in plumes at specific sites and at predictable times, suggesting previously undetected, even unimagined Martian geology and biology. On Earth, about 90 percent of methane is a by-product of biological processes released by living, or once-living, things ranging from bacteria to rotting trees to flatulent cows. That isn’t necessarily the case on Mars, but it certainly is a real possibility.

Scientists are also probing whether Mars was more hospitable to life at its inception than was Earth, which after all did take quite a hit when a Mars-sized body crashed into it and ejected the material that most planetary scientists believe became the moon. And if life did start on Mars, could it have traveled via ejected rock-turned-asteroid to Earth? Bacteria in Antarctica and other glaciers frozen for hundreds of thousands of years come back to discernible life when brought to higher temperatures, and researchers contend they could last in a suspended state (or maybe even carrying on life functions) for millions of years more. Other microbes have shown a previously unimaginable ability to withstand the cosmic radiation of space. Put all this together and the unavoidable question becomes whether, at bottom, we’re all Martians—quite literally descendants of life from Mars. If methane can ultimately be traced to a biological source on Mars, astrobiology will enter an entirely new phase and the quest to find extraterrestrial life will become something more like a race.

Have we actually already found extraterrestrial life on previous Mars missions and in meteorites found on Earth? This is one of the most contentious issues in astrobiology—and in science as a whole—and many highly qualified scientists on opposing sides of the issue are 100 percent convinced they’re right. Feelings are especially high because as astrobiology’s patron saint, Carl Sagan, once said, “Extraordinary claims require extraordinary proof.” But extraordinary proof is very hard to come by, and tantalizing findings are hard to keep under wraps. The result has been a number of long-running scientific grudge matches—intellectual blood sport at the highest of levels, with seemingly many rounds to go. Interdisciplinary cooperation is the mantra of astrobiology but it has yet to repeal the laws of human nature.

The most significant dispute is no doubt over the contested discovery that gave birth to the new era of astrobiology: the 1995 announcement that NASA scientists had discovered a meteorite from Mars that contained numerous features consistent with extraterrestrial life. Critics quickly tore into the report and left it seriously wounded. But the authors have continued their work and say they are more convinced than ever that many Martian meteorites show signs of long-ago extraterrestrial life.

Just as those immersed in astrobiology now theorize that extraterrestrial life does—perhaps even must—exist, astronomers long theorized that planets circled stars in other solar systems. It wasn’t until the mid-1990s, however, that the first definitive detections were made. Now, more than five hundred exoplanets have been identified, seven hundred more are awaiting confirmation, and billions more are believed to exist throughout the universe. As much as any other discoveries, the peek into the world of exoplanets has supercharged astrobiology and encouraged scientists to substantially increase their bets on the existence of extraterrestrial life. But the discoveries have come with big surprises. Most of the extrasolar planets found so far are large gas giants like Jupiter, orbiting close to their suns with smaller but also giant planets farther out—a kind of solar system that virtually nobody predicted. That so many of the planets discovered are in this category is, to a substantial extent, a function of how astronomers are looking for them—bigger and closer to the central star is what we have the technology to detect. But the notion that any Jupiter-sized planets would be orbiting their suns in four or five days was, until recently, unthinkable. Equally unexpected was the discovery that many solar systems consist of planets that travel in wildly eccentric orbits, not the circular or near-circular ones we’re accustomed to. The fact that solar systems come in such peculiar arrangements has both promising implications for astrobiology—with solar systems so varied, the probability is that some others are “just right”—and some negative because planets in those wildly eccentric orbits would probably make their solar systems unstable and uninhabitable.

So the big question for planet hunters is no longer simply how to find planets, but rather how to find more of the smaller, rocky, Earth-sized planets the right distance from their suns to be potentially habitable, and to find solar systems structured in ways that could allow these cousins of the Earth to become nurseries for life. NASA’s Kepler spacecraft was launched in 2009 to make a broad search for Earth-sized planets, and it’s expected to begin delivering substantial results in 2011. But much of the serious planet hunting is being done using Earth-based telescopes, and the ingenuity of the scientists operating them is the stuff of legend. Anyone betting against them finding habitable planets and solar systems has not been following their fevered discoveries.

Astrobiologists are constantly searching for habitats on Earth that can be studied as near cousins to environments that might be found on other planets or moons—the parched Atacama Desert in Chile, the hydrothermal vents of Yellowstone Park and the ocean floor, the dry valleys and deep glaciers of Antarctica. One of the more compelling sites is Lake Bonney in Antarctica, which has a deep covering of ice over liquid water known to support microbial slimes and life. Jupiter’s moon Europa also has a thick layer of ice over what is now believed to be a vast ocean of liquid and perhaps life-supporting water, and NASA and the European Space Agency have proposed it as a major “flagship” mission for the 2020 time period. NASA believes Lake Bonney can serve as a useful analogue to Europa for research purposes, and so it is testing sophisticated submarine vehicles there—autonomous robots whose offspring may well find themselves someday on that moon’s icy surface.

But the study of habitats has a more cosmic meaning, too. Solar systems are now described as having (or not having) “habitable zones”—regions where rocky planets with atmospheres could exist, and where the sun heats the planet to the right temperature for liquid water. Since we now know that the complex carbon-based organic materials that are the building blocks of life on Earth can be found throughout the universe—that they fall on exoplanets just as they fall on Earth—it seems quite unlikely that life wouldn’t start and evolve quickly on an otherwise habitable planet. This, of course, is based on the presumed dynamics of early Earth, our one and only example of a life-supporting planet. Earth is known to have formed about 4.5 billion years ago and to have undergone hundreds of millions of years of meteorite bombardment and generally hellish conditions. Yet early forms of life have been traced as far back as 3.8 billion years on Earth, suggesting that life arose not too long, in geological terms, after conditions became favorable.

In trying to define what makes life possible, astrobiologists are forced to confront another question: Is life inevitable, or the result of a series of accidents? Did the universe have to be finely tuned to make it possible? This is an unavoidable question because the slightest change in many of the basic physical and cosmological laws of the universe would make it an entirely inhospitable place. A minute increase in the extreme weakness of gravity, for instance, would make stars like our sun burn out in 10,000 years instead of 10 billion. If the neutrons found in every atom were not .01 percent heavier than protons found in every atom, then the universe would allow for no chemical reactions because all atoms would be stable and unchanging. Is this kind of “fine-tuning” a coincidence of almost unimaginable proportions? Does it mean the universe itself is the product of a sort of Darwinian evolution? Does it mean there are many, perhaps an infinite number, of other universes that are not organized in a way that can support life, leaving us by definition in the one that can? Or, leaving the realm of science for a moment, is this “fine-tuning” a cosmic reality that supports the argument for a Creator?

The broad-based effort to answer these and many other questions is remarkable because it has finally made it legitimate for white-coated scientists (actually, mostly the blue-jeaned kind) to spend their careers studying the possibilities, locations, and signatures of alien life. Astrobiology projects now attract more grant proposals from members of the National Academy of Sciences (who are invited to join because of their accomplishments and prominence) than any other subject at NASA. In astrobiology today there’s no talk of UFOs, no wormholes or time travel, no giant “gasbag” creatures floating through the upper reaches of Jupiter (as imagined by Sagan himself). Rather, it’s about hard-core science that, until recent years, was technically impossible or simply unimagined, and it stretches from the bottom of deep Earthly mines to the farthest reaches of the universe with its 100,000,000,000,000,000,000,000 (or more) stars, and their unfathomably large number and variety of planets and moons. Even the search for extraterrestrial intelligence, or SETI, has become much more scientifically sophisticated—enough so that NASA and the National Science Foundation have reopened their grant competition to SETI projects, and Microsoft cofounder Paul Allen donated $25 million to begin construction of an array of 350 radio telescopes in northern California designed in part to pick up transmissions from distant civilizations.

NASA has embraced this search, but quietly. Unlike the Apollo missions to the moon, construction of the international space station, or the George W. Bush administration’s proposals to settle astronauts on the moon and send them to Mars, no big announcement was ever made about a new NASA push to find extraterrestrial life—and that’s probably politically astute. Imagine the chuckling and high dudgeon in Congress had it received an expensive and dicey proposal to find ET. A NASA vision statement released in 2002 made this emphasis on astrobiology explicit, declaring the agency’s goals thus: “To improve life here; To extend life to there; To find life beyond.” By 2006, all reference to finding “life beyond” had been removed, but the goal had already been hardwired into the actual workings of the agency.

The NASA astrobiology program was formally initiated late in the Clinton years with a modest budget and a small bureaucracy of its own. The agency’s Astrobiology Institute gives out modest but still very competitive grants totaling about $50 million each year. But that’s only the most obvious effort. NASA and European Space Agency missions are regularly designed with extraterrestrial life in mind. The most eagerly anticipated include the Mars Science Laboratory (designed to scour Mars for signs of the chemical building blocks that make life possible), two joint NASA-ESA missions to Mars (inspired and configured, to a significant extent, by the discovery of methane on the planet), and an increasingly possible NASA-ESA mission to Europa. Then there’s the biggest prize on the horizon—a mission to Mars to gather up rocks and soil and bring them back to Earth for the kind of exhaustive analysis scientists have dreamed of for decades.

As science has found Earth to be a mere speck in the universe, the notion of our human specialness has diminished—perhaps one reason why the centuries-old debate about the existence of extraterrestrial life has at times been so raw. When the discovery of extraterrestrial life comes, the process begun by Copernicus and Galileo in the sixteenth century of pushing the Earth away from the assumed center of the universe will have come full circle. But there is also the strong possibility that astrobiology will introduce people to a transformed understanding of the cosmos and our place in it. That’s what Steven J. Dick thinks. He’s a trained astrophysicist who served for many years at the U.S. Naval Observatory and later as NASA’s chief historian, and is the author of numerous books about the history of thinking about extraterrestrial life. “With due respect for present religious traditions whose history stretches back nearly four millennia,” he suggests, “the natural God of cosmic evolution and the biological universe, not the supernatural God of the ancient Near East, may be the God of the next millennium. … As we learn more about our place in the universe, and as we physically move away from our home planet, our cosmic consciousness will only increase.” Because what, in the end, is nature?

If life is found on Mars or Europa, then isn’t that nature as well? And if carbon-based organic material fills significant portions of space, and is found in meteorites broken free from planets, comets, and asteroids, then isn’t that nature, too? Feeling at home in nature suddenly has a very different, much bigger meaning. That, really, is what astrobiology wants us to understand: that the universe we’re privileged to inhabit is more complex, more fertile, and more mysteriously grand—yet also more knowable—than we could possibly imagine.