Life as We Do Not Know It: The NASA Search for (and Synthesis of) Alien Life

Introduction

His High Exaltedness, the great Jabba the Hutt, has decreed that you are to be terminated immediately.

—Some guy in a funny costume, to Harrison Ford, in Star Wars

It is now one of the most famous barroom scenes in movie history. A dusty town, the darkened bar filled with riffraff (all well-armed and hair-triggered, of course), the wailing loose women draped about, but this is not Deadwood, or Tombstone, or any recognizable place in the Old West. This place comes from the imagination of George Lucas. It is on some backwater planet in a galaxy far, far away, and aliens populate the bar. Lots of different kinds of aliens, by the disparate look of them, aliens independently spawned on a great many different planets. The message was clear. The universe is packed with alien scum, alien heroes, and aliens in between. Or so the filmmakers would have us believe. And believe we did, and still do—untold millions of us.

This iconic scene from the original Star Wars is as good a place as any to begin a book about life, of which earth life and alien life are the two kinds. Modern science has shown that there are certainly enough places to evolve all those aliens found in that nasty bar on the desert planet named Tatooine. Consider, there are perhaps four hundred billion stars in our Milky Way galaxy and perhaps twice that number in our sister galaxy Andromeda. Most stars in galaxies have planets, we are pretty sure, on the basis of the spectacular new work of such planet finders as Geoff Marcy and Paul Butler. So many planets in our galaxy and so many galaxies. Ours is but one of billions. The numbers make it a safe bet that planet Earth is not the only one with life or even intelligent life. So what might all these other aliens be like? Exactly what is an alien anyway?

Let’s return to the bar in the first Star Wars. Obi-wan, Han, Luke, and that big Wookie are surrounded by a variety of aliens, each sporting what at first glance seems to be a radically different body plan from ours. Some have more eyes or different mouthparts, and lots of them have different hands. Yikes, the honchos from SETI (Search for Extraterrestrial Intelligence) here on modern earth would be falling all over themselves for joy. All that money that they spent was not on a fool’s errand! But on further inspection, all the aliens in that bar really don’t look so different from us after all. In fact, you could put a human inside every one of those rubber suits. Is this what makes an alien: a slight (or even major) difference of external body morphology? If we found any one of these creatures on some deserted jungle island or high plateau in the Brazilian rain forest, for example, would we immediately call for Tommy Lee Jones, Will Smith, and the other agents from Men in Black? The truth is, alien life, which we in the astrobiology community have dubbed life as we do not know it, needs more than a picture to be recognized as such. Alien life may or may not have fingers like ours, but it will surely differ in something far more important than body parts. Even blue blood would not qualify one as being an alien; our earthly cephalopods bleed blue, for instance. Something far more profoundly different must be present to qualify a life-form as alien to our familiar earth life. A true alien will differ from us in the most important and unifying characteristic of earth life: whether it has and uses DNA like ours, and even if it has DNA, whether it uses the same genetic code as we do and makes proteins with the same amino acids, among many, many other possible differences that are potentially possible.

Where will we have to go to find an alien if we use that kind of definition for alien life? Mars? Titan or Europa? The next star system? How about here on Earth? Surely this latter suggestion is whimsy. Where could aliens be hiding here on Earth, other than in secret Nevada military bases? In fact, the nearest aliens might be right here, under our noses, even in our noses.

This seems like a startling heresy. Since Darwin famously said it was so, all biology texts proclaim that all earth life came from a single source, that all is united by common ancestry. In other words, ever since Darwin it has been scientific gospel that all life on Earth is of the same basic type: No aliens here, thank you! However, we do not know if that is, in fact, true.

Here is the best that science can tell us: There may be lots of aliens (life as we do not know it) lurking here on Earth. How would we know if we ran into such life? Only the equivalent of a blood test will tell us. Here we run into the most interesting irony. We use DNA tests to establish the family tree of life on Earth. Aliens, even terrestrial aliens (an odd concept), would not show up as life under such tests. Maybe we need the men in black, right here on Earth, more than we know.

What we do know—with our heads, if not our hearts—is that each of those supposed aliens in the Star Wars bar is but a human in a rubber suit or the mirage produced by fingers running across some special effects-producing keyboard. But it is possible—not probable, but possible—that even if every one of those alien Star Wars desperadoes was spawned on a planet orbiting a star other than our sun, none of them would be an alien because it is possible that all life in the Milky Way galaxy has DNA identical to ours. Hence these so-called aliens are really different from earth life only in their comparative morphology, not the real stuff that makes one an alien. DNA might be one way to make life—or the only way. Life in fact may have spread throughout the galaxy by natural methods and is united in its origin and DNA, a hypothesis more than a century old known as panspermia. At this time, stuck as we are in this lonely and separated star system, we cannot know. Sadly, we may never know—about life on planets orbiting other nearby stars, that is. The distances may be too great, even with our amazing technology. There may never be a warp drive, or faster than light speed drive, or whatever it is called in the movies. Perhaps the stars will always be beyond our reach, something never seen in the sci-fi movies. But knowing if there is life on our own planetary companions, and indeed if there is alien life here, now, on our own planet, is another matter. We will know, and soon, if there are aliens in the solar system. NASA will see to that. It is busy spreading its probes across the reaches of our sun’s planets even now: Mercury, Venus, Mars, Saturn, Pluto—all are the current targets, and soon we shall return to Jupiter.

So if we cannot (yet) find aliens, why not make them, while we wait for the first Mars sample return mission, scheduled to bring soil from Mars back to our earth in but a few short years from now? Here our sci-fi space epic morphs into Frankenstein, only updated. As I write this, several labs around the world not only are furiously trying to make life—life, in fact, as we do not know it—but have already done so—made alien life, in fact. So out of the bag, damn cat. There are aliens in existence, if we count life that does not share our specific kind of DNA, amino acids, and proteins as being an alien. That too is a subject of this book.

The time is thus right to take a new look at what an alien might be. A new and concerted effort by NASA has made respectable what was once fringe and pseudoscience. In September 2002 and again in May 2004, some of the best scientists on the planet were assembled at the behest of NASA and the National Academy of Sciences to compare notes about alien life. These scientists asked brash new questions, and not a few wondered if indeed DNA-based life is the unique type of life on Earth. They asked if there might be either fossil or extant life in our solar system that also qualifies as life as we do not know it. They asked too if NASA and the other space agencies, which have already poured billions of dollars into current and upcoming missions (to Mercury, Venus, Mars, and the Saturnian system), are building the right machines, visiting the right planets and moons. They are posing brazen questions about the possibilities of alien life. There is reason for optimism if you, like me, hanker to really know if we are alone. On the basis of masses of new data and insights, the solar system seems a far more biologically friendly place than was assumed even in the last years of the twentieth century.

Thus the time seems propitious. But why did I choose to write this narrative, and what can I bring to the subject? It takes only a quick look at the bookshelf in my office to find a score of reasons for why not. In the past decades there have been numerous and monumental books on life’s origin and definition, by a parade of humanity’s most gifted: Erwin Schrödinger’s What Is Life? Jacques Monad’s Chance and Necessity; Francis Crick’s Life Itself: Its Origin and Nature ; Christian de Duve’s Vital Dust; Paul Davies’s incomparable The Fifth Miracle; and Freeman Dyson’s Origins of Life, among many, many others. I make no pretense to be in the intellectual league of these luminaries. But all these books are about how life formed on Earth (and about what life is). And while there is also a huge group of books about the environments on the planets and moons of our solar system where life might begin, there are few books that are a fusion of the two, using the knowledge of what earth life is and how it formed on Earth to inform us about the probabilities of life in the solar system. My sense is that progress can be made at this moment by a new analysis that is informed by both topics.

I also come to the debate as an acknowledged skeptic about alien life, and who better than a doubting Thomas to take a dispassionate look at life in our solar system? Near the end of the last century I spent three years writing a book with my colleague Don Brownlee about the potential frequency of aliens. Rare Earth: Why Complex Life Is Uncommon in the Universe was published in the first days of this new century. The center of that book is what we call the Rare Earth Hypothesis, which is really two hypotheses. First, microbial life is relatively easy to evolve from nonlife; has a wide range of tolerance in such conditions as temperature, pH, and pressure; and therefore should be found widely throughout habitable planets and moons in the cosmos. Second, most such planets and moons remain habitable for only short times or are never suitable for higher life to live on, and thus complex life (which invariably seems to be more fragile than simple life and requires ever more and narrow environmental conditions to survive), the equivalent of our animals and higher plants, will be very rare indeed.

In the blissful, now sadly departed pre-9/11, pre-Iraq War, and pre-SARS days, our book, for whatever mysterious reason, became widely publicized, aided in no small way by the howls from the SETI organization, which, like the science fiction industry, depends on a belief in aliens for its economic viability and thus saw our book as a personal affront and attack. From that point onward I was (and continue to be) viewed as the number one skeptic about life in space, and I am usually wildly misrepresented as suggesting that life, or even just intelligent life, is unique to the earth. That is ironic, and it comes from those unfamiliar with the book, for Rare Earth was more about why simple life should be common than about life’s rarity. Nevertheless, I do approach the subject of life in space with conservatism.

Why is it that there seems little hope that we will find Wookies (or their animal-like ilk) on every planet—Mars, for instance? Could H. G. Wells, SETI, and a thousand followers positing inimical Martians and untold other nasty (and biologically complex) aliens have gotten it so wrong? I do think so—because they have looked up at the stars, rather than at the rocks beneath their feet for primacy of information about life in space. The reasoning behind the Rare Earth Hypothesis came not so much from astronomy (although there was plenty of it necessarily there) as from new information from oceanography, geology, and paleontology—important players in the then newly forming science called astrobiology. In Rare Earth, Brownlee and I suggested that while the sheer number of stars with their inevitable planets would make the existence of at least some other intelligent civilizations a near inevitability, their probable small numbers would space them apart in the cosmos at such vast distances that it would be unlikely that one intelligent civilization would ever even detect the presence of another, let alone meet it face-to-face, or face-to-whatever an alien meets with. We defended this view by describing the geological and planetary mechanisms that allow the earth to maintain its life, such as the overriding importance of what can be thought of as a planetary thermostat of planet Earth, a geological mechanism involving plate tectonics and the movement of carbon from rocks to atmosphere and back again. We described how the combination of stable temperature for billions of years and a low number of mass extinctions (which can be thought of as potential planetary sterilization events) in the past had combined to allow the earth the time necessary for the evolution of animals and higher plants from the original microbial stocks. We asked how similar conditions might persist on other worlds, and we pondered the set of conditions that might allow other worlds to maintain long-term temperature and atmospheric stability. It seems that many separate conditions are necessary for a planet to remain habitable for long periods of time.

But critics of the book (and they remain legion!) rightly pointed out a most crucial point, a variation on what is known as the anthropic principle. Rare Earth dealt only with a narrow segment of life, something that could be called earth life, sometimes referred to as life as we know it or DNA life. This type of life, the argument goes, would necessarily require a planet much like Earth for its survival, and all acknowledge that there are probably few exact duplicates of Dear Old Earth. Yet the universe is large, and our solar system and the earth are small. The very immensity of the universe, with its myriad galaxies, must allow for an enormous diversity of life, according to those who believe that there are a vast number of aliens and alien civilizations in space. Not diversity of life, as we understand that phrase applied to life on this planet. All biologists agree that there are millions of species on Earth but that all sprang from a single common ancestor and thus are but one type of life: DNA life. Yet it is surely possible that there must be a multitude of types of life differing in their most fundamental properties of chemistry and metabolism. Such life would not have DNA, or perhaps even carbon as a constituent, like the oft-discussed staple of science fiction silicon life. Such life indeed might be life as we do not know it.

With the vastness of the universe and the large number of distinct chemical elements found throughout it, surely it is reasonable to suppose that all manners of life are possible. But is this really true? How diverse can life really be? How about boron life? Or tin life? Or life without any matter at all, like some form of pure energy life? With a bit of imagination almost any type of life can be suggested. But life is not a simple proposition. It may be the most complex of all chemical systems in the universe. It seems to me that there is a reasonable possibility that there might not be many ways for life to be constituted at a fundamental chemical level. In fact there might not be anything except carbon-based life-forms. And in an even more restricted sense, DNA might not be just one way but the only way. So, if not DNA, what? Perhaps all life uses DNA, perhaps with a different language or syntax in its meaning, but DNA nevertheless. This point of view cannot be disproved at the present time, a sad commentary on how little work about the chemistry of life has actually been accomplished.

To ask about the diversity of types of life requires that one looks at another, even more difficult question. How could anything as complex as DNA have come about naturally, on Earth or any planet? It is not enough simply to arrive at a chemically permissible form of life. Any discussion of aliens must ask how they originated.

How life formed on Earth is indeed one of the great (some say the greatest) scientific mysteries, a problem perhaps even more important than the mystery of how common life is in the universe (indeed, the latter question is an offshoot of the first). There are currently two schools of thought concerning this origin of life problem. First, some deity did it. That one cannot be disproved with science, so has no further place in our story here. Second, life formed on Earth (or was transported here, but this just begs the question of where and how it first formed) through some chemical pathway within a specific environment at a specific time. This view has much scientific information to support it. Many scientists now believe that life might be an inevitable consequence of this particular universe that we live in. Life appeared on Earth relatively early in earth history, certainly no later (and perhaps much, much earlier) than about 3.7 billion years ago on a planet that coalesced into existence about 4.6 billion years ago. This suggests either that our planet was very lucky or that life—at least as it was on a planet like Earth early in its history—is not so hard to make.

These two threads—what life could be and how it could form—are thus the intertwined themes that I shall explore in the pages to come.

Finally, I am in an interesting position to tell this story. In 2001, on our second try, the University of Washington won a highly competitive five-year grant from NASA to join the NASA Astrobiology Institute. I was (and am) the principal investigator of the University of Washington node of what we call NAI (made up of fifteen research institutions around the world), and in this position—being a member of the NASA organization, yet not being under the umbrella of the organization to the point that I cannot speak about both the warts and the wonders of NASA efforts—I have seen from a wonderful vantage many of the discoveries and concepts that will make up this book. A not insignificant part of the work to be discussed has been funded by the grant that I administer, and some of it is my own. Many of the people who have made contributions important to my narrative are members of the University of Washington NAI team, and if it becomes tiresome to read about yet another discovery from that team, then they have done their job well.

It has been wondrous to see the workings of creation (as the laws of physics and chemistry might be called) and know that there must have been multiple, and separate, creations, all the workings of planetary chemistry sets—some of them, perhaps, the best thing ever evolved by our species. Or the most dangerous, if artificial life eventually comes back to bite the hand that invented it.

One of the most important messages that I wish to present in this book is that there has been significant progress in the artificial synthesis of life. While pundits routinely pontificate that science will never succeed in creating life from scratch in some equivalent of a test tube, quiet progress on many fronts begs to differ. The question is thus not, Can we make life, but should we? Should we make life that has never evolved through natural selection, life using chemistry that is a nose thumb to Darwin? We are in the post-9/11 world, of course, so we have to ask if this new life can be dangerous: Can it be made into a weapon? Can it be made into a tool that does the opposite of weaponry: helps humanity with food, or with pollution control, or in fighting disease? Or should it be done simply to show that life other than that evolved on Earth is indeed possible? What if we could build a life-form that could live at -150°C—essentially the temperature found on the moons of Jupiter and Saturn—and thus demonstrate that life could indeed live in these cold freezers of the solar system? This would prove that life could live in such cold places, and we would be ready to look for it. These would really be aliens. This is something that I wake up worrying about, in the dark of the early morning, the time of nightmares, for I am working toward the construction of such aliens. What if it mutates, takes over the Arctic, and then spreads south toward the winters of our populated world? Should scientists play God, even if it is a Jack Frost god?

Could there be earth life on any or all of these bodies beyond Earth? And if not earth life, any—or what—kind of life? In a wonderful story by Robert Sheckley, a poor human astronaut stranded on Mars stumbles onto an abandoned (and somewhat intelligent) Martian village. By shaking out some loose crumbs from his pockets, he makes the village understand what sort of food (and water) he needs to stay alive. But this type of material is in very short supply on Mars, and in trying to make the food and water that he needs, the village starts to destroy itself. The punch line of the story is that the earthling gives himself up to the village and is transformed into a Martian, who no longer needs water. There is a message here. We too often look for earthlike conditions, because that is what is needed for earth life. What about the burning worlds like Mercury and Venus? Or the frigid wastes on Mars, where there is virtually no liquid water, temperatures are forever below zero, and even the soil contains antibiotic chemicals? What would be the ideal chemistry of life? Or on Titan, where it is even colder and harsher? What sort of life, if any, would thrive there? What about farther in space, on a comet, perhaps? Each of these places has been the focus of a recent NASA mission of some sort, with only Europa not visited in the last year. For each, there is startling new information that pertains to the question of life in the universe. Earth life works wonderfully well on Earth. But elsewhere?

We may never find Wookies, but what we find, and make, will ultimately be far more interesting than a tall man in a hairy suit. So let us begin.

Chapter 1

What Is Life?

From a commonsense viewpoint, nothing seems easier than to tell what is alive and what is not.

—Gerald Feinberg and Robert Shapiro, Life Beyond Earth

The small submarine headed down toward the blackness of the deep sea bottom, thousands of feet below, and the cramped men inside could only wait out the seemingly endless descent, passing the time by peering through the Alvin’s thick glass port-holes. The voyage began in the sunlit portions of a sea filled with life modern in aspect but then descended back through the ages, for the deep sea is the home of many living fossils, species of great antiquity. Finally the voyage landed at the site where life may first have started, a place that might still harbor microbes that were present when DNA life first arose. Such a place might harbor other life as well, the predecessors of our familiar DNA life. But at what point as we go back do we reach the transition from life to nonlife? That particular question was about to become even more problematical on this day in 1978.

At first, the rich fauna of the daylit upper reaches of the subtropical Pacific surrounded the submarine: clouds of plankton, most evolved from the Cretaceous period on; schooling small fish and the larger piscine predators that pursued them, relicts too of the Cretaceous period; umbrellas of jellyfish and their ilk, from vastly older stocks, but made up of species that might be very recently evolved; the shooting forms of arrowworms; the darting and resting of crustaceans that seem even more modern than the fish in these sunlit seas. Farther downward the submarine descended, and the brightness and color of the sea changed, a gradual journey through the spectrum of blue in all its shades toward ever-deeper hues. Now life was less noticeable and different in aspect. The sardine shape of the fish changed, as did the look of the invertebrates, and now, at least to a paleontologist, the world looked more Mesozoic than otherwise. An occasional squid appeared, and even these no longer looked like their familiar surface-dwelling cousins. Long tentacles draped from the head regions in some, while others had squat, ammonia-filled bodies resembling tiny hot-air balloons. These exotic squid were probably the closest living relatives in both ancestry and ecology to the vast race of the extinct ammonites, poor victims of the end-Cretaceous asteroid, and they themselves were of great age. Here in the mid-water now, in a place as far from the bottom as from the top of the sea, there lived a fauna that depended on flotation sacs to keep it permanently suspended—a fauna from antiquity. Through the windows of the small sub, deeper now, more than a mile beneath the surface, the scientists could see undulating floaters, or slowly swimming invertebrates giving off rainbows of shimmering color. Deeper still, approaching two miles deep, small lights, like drifting stars, amid the surrounding pastures of life, not unlike fireflies at dusk on a warm Ohio evening, began to appear in the darkness. The larger carnivores—the peculiar fish and squid of these great depths—some amazingly grotesque with huge mouths lined with sharp teeth, on occasion passed by the windows. All were countershaded, with light-lit bellies and dark upper surfaces, so that anything above them would see only black, and anything below would not notice their silhouettes against the faint light of the far-distant surface. All had a shape that comes to us from the distant Paleozoic, when the platy placoderms and armored arthrodires known from spectacular fossils recovered in the Cleveland shale or Old Red Sandstone evolved the peculiar heterocercal or reversed shark-shaped tails that are found only on these deep-living species and on the fossils from the four-hundred-million-year-old seas of ancient planet Earth.

As the deep blue of the tropical sea lost finally all color and was replaced by velvet night, the great searchlights of the Alvin switched on, bringing bright light to a region that had been unlit for millions of years, and the sub finally reached the bottom, a journey down, and one seemingly back in time, to the dawn of life on Earth. An hour had passed since the submergence. After the seemingly endless descent, when the men’s imaginations had already cataloged the many ways that the submarine could fail its fragile inhabitants in the pressurized and cold depths, the bottom was finally spotted. Stark, lifeless, it resembled all the sea bottoms from the time before the Cambrian explosion, that moment 550 million years ago when the animal phyla sprang into existence. For 3.5 billion years prior to that moment all sea bottoms had been barren of any life but microbes, barren like this one.

For a time the Alvin glided over this desert sea bottom, a vision, perhaps, of what the deep-sea bottom of Europa might look like, surely also a smooth expanse of sediment in absolute darkness, but is it, or even this sea bottom, really lifeless? Then, shockingly, the smooth mud of this deep Pacific Ocean bottom gave way to a lithic landscape. A tangled rocky wilderness, the land of the submarine volcanic vents, lay illuminated below the Alvin. The bottom was like a disordered junkyard, with vast fields of pillow lava and twisted toothpaste squeezes of now-solid rock covered with a patina of sediment. The Alvin was about fifteen feet above the bottom now as it powered over the endless fields of volcanic rock, when its startled humans found themselves among a sudden profusion of animal life, one unlike that of the surface regions. It was a vent fauna, the strange animal fauna that had first been seen only two years before during dives in the Galápagos Islands. But those dives had been on a bottom far more peaceful than this one. This water became hazier, filled with dustlike particles and larger flocculation of repulsive-looking slime. Now there were tube worms, and white clams and crabs, and catalogs of other invertebrates unknown to humanity. In the worms and crabs and clams there was no doubt that the Alvin had found life—weird life, of course, but unambiguous vessels of earth life. But what of the floating slime, the white snowflakes that clouded what had been a pristine sea only minutes before? What was this material? Was this life?

The rocky bottom became more dissected, with walls and deep, narrow canyons appearing. The rocks in this new canyon land were covered with brown growth—mats of microbes?—and while the occupants of the small sub could not know it, much of the microbial slime that they viewed amid this deep rocky rubble was, like the larger animals, composed of living fossils, but in this case, species not of some Paleozoic age but of a far more ancient time, the time of the earth’s youth, time measured in billions, not millions, of years. Suddenly and unexpectedly a tall spire of rock appeared dead ahead. It was covered with life, but the scientists looked at something far more