Chapter Breakdown: [ NEW WAYS OF LOOKING AT LIFE - COMPLEXITY: WHAT'S THE BIG IDEA? - LOVE THAT DIRTY WATER - LIFE OUTSIDE THE KEY OF C? - LOOKING FOR LIFE UNDER THE STREET LIGHT - LIFE ON VENUS: AN AGNOSTIC VIEW - FISH TALES - STRANGE FRUIT - LIFE SIGNS? - IS VENUS COMMONPLACE? - ARE WE ALL VENUSIANS? - LONG LIVE MAGELLAN - BACK TO VENUS - A LONG HOT VENUSIAN AFTERNOON - OH WE, LIKE CATS - TERRAFORMING AND VENERAFORMING - OUR PLANET OURSELVES ]

	"The totality of life is merely a fancy kind of rust, afflicting the surfaces of certain lukewarm, minor planets" --H.J. Muller
	"It is with difficulty that we begin to grasp the mechanism of this transformation of solar energy into terrestrial forces. Its phenomena, which we are accustomed to regard from another standpoint, deceives us by the infinite variety of color, form and movement which are inherent in nature and of which we ourselves, through our life, form an integral part." --Vladimir Vernadsky, The Biosphere, 1926
	"Cause you never can tell What goes on down below. This pool might be bigger Than you or I know!" -- Dr. Seuss, McElligot's Pool

New Ways of Looking at Life
Is there life on Venus? Could there be life on Venus? The standard answers are "No and NO!". Venus is usually dismissed in a paragraph or two before an extensive discussion of the prospects for life on Mars, the icy moons Europa and Titan, and Earth-like planets elsewhere in the universe. Where life is concerned, Venus is consistently voted "least likely to succeed". In my opinion, this quick dismissal is not justified. It presupposes knowledge of the universal nature of life and the general characteristics of inhabited planets; knowledge that we do not yet possess.

Life is usually assumed to require organic molecules¹ dissolved in liquid water. Discussions of the habitability of other places in the universe have focused almost exclusively on the likelihood of finding planets with climate and atmospheric conditions that are "just right" for us.

By this standard model, Venus is obviously sterile because it is too hot and dry. But I think it may be premature to declare Venus off limits to life. I know that some may find this viewpoint ridiculous or even irresponsible. It could get me in hot water with some of my colleagues, but that's OK. Hot water, as a symbol for domains that are off-limits to life, is a very appropriate metaphor here.² In our present state of ignorance we should avoid all dogma in exobiology (the study of possible life beyond Earth).

Part of the problem is that it's difficult to define life, so how do we go about looking for it on other planets? Life is like a standing wave in a swiftly flowing stream--a stable structure through which matter and energy flow. If we are going to look for it around the universe, however, we need a more specific definition. Usually we define it as something like "a self-propagating chemical system that adapts to its environment." Two recent scientific movements suggest refinements to the definition, putting some new spin on our ideas about habitable places elsewhere. These two new developments are Complexity and Gaia.

I've already discussed Gaia in connection with life's possible role in Earth's evolution, but this perspective is also valuable for thinking about life elsewhere, and how we might recognize it. Gaia has its roots in the ideas of a remarkable Russian geochemist named Vladimir Vernadsky, who described the "biosphere" as that part of the Earth transformed by life. He defined life as a planetary property, as the way the Earth's surface responds to sunlight, covering itself with blue-green algae, forests, prairies and eventually parking lots and shopping malls.³ "The Earth is literally covered with an uninterrupted film of living matter", Vernadsky wrote in 1926. He described how this zone of life had modified the planet, facilitating further development of life, and how life's participation in numerous geochemical cycles dominated the appearance, structure and chemical state of Earth's surface and atmosphere.

More recently the gaians have written of "geophysiology," describing mechanisms of self-regulation by which life may be actively controlling the climate and other conditions on Earth. Some of the details are still quite controversial. In particular, the extent to which life is really in control of Earth's overall environment is subject to continued debate. But the Gaia hypothesis has motivated a lot of good research into the intricacies of life's role on our planet.

It cannot be denied that life has fundamentally altered the appearance, atmosphere, climate and chemical composition of the Earth. Our world is awash in life. Interacting communities of organisms create one another's environments, and this "world wide web" shapes and is shaped by the Earth. In a very real and tangible way, then, the Earth--all of it--is part of this circulating, self-perpetuating, complex, evolving, breathing, growing, dying, talking and dreaming thing called life.

The biosphere is a feature unique to our planet, so far as we know (which isn't very far at all). Life has a hold on the Earth and may never give it up, until the sun expands and consumes us five billion years from now. By then we may be long gone, watching the sun's dying pyrotechnics from a safe distance.

Life leaves its traces even in the "non-living" parts of Earth. Everywhere we find patches of chemical and physical complexity dropped by life in its haste. Life is so full of life that it occasionally spills it on the ground, leaving distinctive signatures of isotopes and chemicals, or structural patterns and rhythms for us to find. Should we find similar signatures and patterns on other inhabited worlds?

According to the Gaian view, life is a process that, once it gets started, becomes intimately involved in the later evolution of its home planet. Any inhabited planet should be brimming over with life, and life should have affected it physically in ways we might observe.

This overall concept has merit: but do we know enough to make specific predictions? The Gaians have made a nice first attempt to define the properties of inhabited planets. Their criteria, though, are of necessity heavily based on the example of Earth. They claim that we can tell whether a planet is inhabited from the composition of its atmosphere. Inhabited worlds have atmospheres that are out of equilibrium.⁴ Equilibrium equals death. They note how Earth's lively, cycling atmosphere, far from equilibrium, is deeply related to the planet's capacity to support life and the effect that life has on the planet. This is contrasted with the "dead" worlds of Mars and Venus, which they portray as static, in equilibrium, with atmospheres that are "just sitting there." This may be true of Mars, but this view of Venus is outdated. Like Earth, Venus seems to possess lively chemical flows and cycles that may actively maintain the atmosphere and clouds.

One problem with the "disequilibrium" criterion for inhabited worlds is that it is vague. The atmosphere of Venus is definitely not in equilibrium. It is closer to equilibrium than Earth's, but how far from equilibrium must an atmosphere be before it is considered alive?

Another problem is that there are many nonbiological sources of atmospheric disequilibrium, such as lightning and ultraviolet radiation, even on the few planets we have studied. Furthermore, not all life creates chemical disequilibrium. On Earth, plants do, but animals do the opposite: they eat disequilibrium and excrete equilibrium. With every breath you take you inhale oxygen and exhale carbon dioxide, bringing the Earth's atmosphere a bit closer to an equilibrium state. Life giveth disequilibrium, and life takes disequilibrium away. So, do we really know what to look for? Shouldn't an atmosphere suspiciously close to equilibrium be just as likely to signify life?

In fact, the atmospheres of Venus and Mars are both "suspiciously" close to equilibrium. They are dominated by CO₂, yet in their upper regions ultraviolet light naturally breaks up CO₂, creating CO and O. Given this, atmospheric chemists have had some difficulty figuring out why the CO₂ atmospheres of these planets are stable. We would expect both planets to have a lot more CO and O₂ and less CO₂. Is this a sign of life on these worlds? Are there creatures that breath in CO and O₂ and make CO₂? Probably not. We think that we've found natural chemical pathways that reunite the broken CO₂ molecules.

This example illustrates why is difficult to infer the presence of life from "strange" atmospheres. We don't know enough about non-biological or biological atmospheric processes to make sweeping statements. However, it's good that people are starting to think along the lines of a biosphere as something with planetary-scale properties. This helps us to think about what properties inhabited planets may have, and how they may differ from lifeless worlds.

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Complexity: What's the Big Idea?

	"You got to stand and face it. Life is so complicated." -- Ray Davies
	"The truth is rarely pure, and never simple" --Oscar Wilde
	"Matter awoke and organized itself. The flame gave way to music". --Hubert Reeves, Atoms of Silence

You've heard of the second law of thermodynamics: Entropy always increases. Things fall apart. If you don't keep cleaning your house it will become hopelessly messy. All the king's horses and men can't put Humpty Dumpty together again.

But how did Humpty get put together in the first place, if the universe always tends towards disorder? There are local tendencies towards increasing complexity and order which do not violate the second law, because it applies only to closed systems. If entropy (disorder) is lowered here, the universe pays for it somewhere else.⁵ In our open system, Earth, life feeds off of the sun. It takes energy to make ordered structures like us.

Actually, it takes a flow of energy or matter to keep an engine, a life form, or a biosphere running. As we discussed in chapter three, flows always create differences, or gradients⁶, a simple form of order. An engine or a life form feeds off a gradient in heat or chemical energy and always acts to reduce that difference. Without a continual input of new energy from outside, life forms and machines will erase all gradients, run down and die, producing a state of minimum order and maximum entropy where nothing changes. It can also described be described as a state of complete equilibrium. Pretty boring if you ask me.

The universe tends towards death and disorder. It's the law. But look out of any window or down at your toes. Our world is fantastically ordered and alive. Somehow, on the surface of the Earth, the flow of solar energy is transformed into the fantastically complex ordered system of the biosphere. Why here?

In some circumstances, patterns seem to emerge spontaneously from the flow of energy. The effort to understand how order comes from chaos, has lead to the creation of a field called non-equilibrium thermodynamics. It was pioneered several decades ago by Nobel Laureate Ilya Prigogine, who coined the term dissipative structures to describe the forms that arise spontaneously in flows of matter and energy, dissipating energy and creating order along the way.

A simple dissipative structure, one we have seen many times in this book, is a convection cell, in which heat flowing through a system organizes itself into discrete patterns of upwelling and downwelling matter. This organization can be very simple or more complex. The weather patterns in planetary atmospheres are dissipative structures created by the flow of solar heat. The flow of heat out of planetary interiors also results in the spontaneous organization of convection cells. Whirlpools and tornadoes are dissipative structures, pockets of order created within energetic flows.

Non-equilibrium thermodynamics also helps explain how the fantastic complexity of life on Earth can have arisen in a universe that tends towards disorder. Convection cells are the simplest example of dissipative structures, organisms and biospheres the most complex. This tendency of matter to use flows of energy to form complex structures, in apparent local defiance of the universal second law, has also been called self-organization.

Have you heard any of the ruckus surrounding the new scientific field of complexity theory? It is the mathematical study of self-organization, a direct intellectual descendent of non-equilibrium thermodynamics, that was born with the advent of computers big and fast enough to simulate some of the complex processes in the real world.

The complexity theorists use computer simulations to mimic the emergence of order in natural systems, trying to develop an understanding of the principles governing the "emergent properties" that arise from matter in certain circumstances. I say "trying" because no one has yet developed an overall theory. But they have demonstrated intriguing similarities in the properties of many different kinds of complex emergent systems, including life-forms, ecosystems and societies.

We've all observed emergent properties. Sometimes a new behavior arises from interactions among the elements of a system--a new quality that resides more in the patterns of mutual interaction between the components than it does in the components themselves. One example is a phase change. When ice freezes or melts, the individual water molecules remain the same but their interactions change. Emergent properties can arise in groups of human beings, too. When a basketball team suddenly gets "momentum", it is something that happens to the team collectively and can't quite be explained by, or reduced to the actions of individual players. Suddenly their passes are connecting, they are hitting the basket. They are on fire, as a team.

The scientists involved in the complexity movement are attempting to arrive at a new way of describing the emergence of biological order. They see life as an emergent phenomenon that arose on Earth due to the right conditions, involving flows of matter and energy and the availability of chemical building blocks able to tap the potential for order. They may be laying the groundwork for a theory of life that does not depend on the details of conditions on Earth a "physics and math of evolution and metabolism."

Complexity does not threaten to replace Darwinian natural selection or render it obsolete, but it may augment it in ways that could throw new light on the marvel we call evolution. Darwinians speak of the "blind watchmaker" of evolution, which selects from completely random variations over long periods of time. The "mistakes" in the genetic code that enhance survival naturally tend to propagate themselves, and thus life slowly evolves. But some complexity theorists are now questioning whether the watchmaker is truly blind. They suggest that since nature seems to spontaneously seek order in some situations, this emergent behavior might be behind a lot of biological innovation. In their view, natural selection chooses from among a menu of spontaneously ordered options. Maybe the watchmaker of evolution is not completely blind, or is at least guided by some pattern-forming habits built into this universe.

That may explain why so many biological shapes are fractals. Fractals are forms with self-similarity across scale, that is, shapes in which the smaller parts are the same shape as the whole. Some examples are branching trees, spiraling sea-shells, and your nervous and circulatory systems. The most famous fractal of all is the Mandelbrot set. You know, those baroque, day-glo⁷, Dr. Seuss-on-mushrooms designs you've seen on T-shirts and in music videos. These infinitely intricate patterns are all created from a simple mathematical equation, repeated over and over again on a fast computer.

The Mandelbrot Set and other computer generated fractals often seem remarkably familiar. You watch fractal videos and think "There's a sea-horse", or "there's a line of marching tigers". Why do the shapes of living things on Earth seem to have so much in common with these mathematically generated forms?⁸ Fractals are a kind of geometrical complexity. Complexity theorists have found that many emergent self-organizing systems create fractal shapes.

Fractals are made by simple equations in iterative computer programs: the product of one round of calculation is used as the input for the next step. This is the mathematical equivalent of feedback, of a nonlinear process. Probably nature likes to make fractals because many natural growth processes are iterative. Somewhere their "instructions" contain the command "Go back to the previous step and repeat until done." For whatever reason, nature seems to love to assemble itself into fractals.

When you start looking for fractals on Earth, you see them everywhere. You see common geometrical forms in life from the micro to the macroscopic scales. The same shapes appear in life made from very different materials, on land and in the sea. Fractal forms seem to arise from basic physical constraints on growth processes, universal physical realities. Whatever generates fractals may be deeply impeded in the rules of life, quite possibly deeply enough to transcend worlds. When we do finally meet the aliens, maybe they won't look completely unfamiliar! Anyone who has spent time looking at the Mandelbrot set might respond to the first pictures of alien life by saying, "Oh, I've seen THAT one before!" [visual of part of mandlebrot set, Ernst Haekel drawing of micro-life, and Tory Read photo of fractal plant life at Botanical Gardens]

One possible answer to "what is life?" is "I don't know, but we'll know it when we see it." We might look for life on other worlds by examining photographs for well developed fractals. This search strategy assumes no particular biological mechanism, which is good given our ignorance and nature's inventiveness.

Of course there are geological forms, like branching rivers, that look fractal but are not necessarily related to life. Complexity theory would need to advance to the point where we can reliably predict which kinds of fractals are biological ones before we could make use of this strategy. Here is a prediction: We will find fractal forms, and they will seem familiar to us, when we find life on other worlds.⁹

Critics attack complexity theorists because they don't (yet) have a unified theory encompassing all the bits and pieces of this new research direction. They do, however, have a lot of intriguing results that are worth getting excited over, even if no one knows quite where it is all leading. Complexity represents a new way of looking at nature that doesn't quite fit the rules of science as it has been done. For example, it is inherently non-reductionist, focusing instead on emergence. One of the objections is that it is not predictive--at least not yet, in the way that science has required itself to be. Maybe in some sense it is not even science but natural philosophy. In any case, it is an important new way of looking at things that have traditionally been the domain of science. Complexity seems to be able to describe a surprisingly wide range of natural phenomena underneath one emerging branch of theory. We could miss out on something important if we dismiss it rhetorically because it provides no unified, predictive theory, or because it does not fit the old rules.

This dialog on the value of complexity is interesting to watch because it is a battle of cultures or even world-views within science. The debate is not just about whether certain theories are right, but about a way of looking at the world, and even the boundaries and definition of scientific thinking. To the extent that it's not science, science may reveal itself to be inadequate to deal with some territory that it has traditionally claimed. In this contest, I put my money on the "complexologists".¹⁰

Is life implicit in the laws of physics?¹¹ Does the universe have an inherent capacity or a tendency to become alive, given the right conditions? Many people have said that it does, that life has been in the universe from the word "bang." We have no way of saying for sure, at least given what we know now. We can poke around the edges of this question with science, but it is also fair game for intuition and faith. I feel fairly certain that the universe wants to be alive, that the arrival of consciousness here, and probably elsewhere, is inevitable. We are the universe waking up. I do not have any strictly scientific arguments to support this, but everything I know and have seen of this universe, informed and enriched by all my scientific studies, as well as direct experience, contributes to this viewpoint. I prefer not to believe that we are the only conduits for consciousness in the entire universe, not because I have any evidence to the contrary, but because the notion seems absurd to me. It's largely a matter of aesthetic preference. One of the exciting implications, for me, about complexity theory is that it may represent the beginnings of a quantitative theory that could address this question.

The current paradigm of exobiology has been around for about 30 years or so: life is carbon based, made by chemical evolution of organics in water. Earth-like environments are the only places where life can really be expected to flourish. You have to wonder, though, about any theory that concludes that our kind of life is the only kind, and that our planet is uniquely qualified to become alive. If complexity theorists can develop a general theory of living systems, maybe we will have criteria less dependent on our experience within the biology of only one world.

Perhaps a combination of ideas from Gaia theory and Complexity theory can help us to think more generally about planets as environments for life. Gaia encourages us to think of a biosphere as a global property that certain planets might possess. Complexity suggests that life emerges spontaneously amidst the right kinds energy and matter flow, and where conditions are suitable for stable structures to form and last long enough to perpetuate themselves.

What would make one planet better than another as a place for a biosphere to grow? Before we plant a garden, we till the soil, turning it over to ensure that nutrients are brought up from below and air is mixed in from above. A planet like Earth tills its own soil, with its constantly cycling interior, surface and atmosphere. This activity keeps nutrients and energy sources constantly available, making the surface of Earth a fertile place, a good niche for life. Planets like this may be likely to form biospheres as a natural consequence of their physical evolution. Perhaps an active, overturning surface, and an atmosphere with dynamic chemical cycles will prove to be good qualities for living worlds.

Even if you removed life, Earth might still seem like a living system, with its complex interweaving feedback cycles of matter and energy and many chemical reservoirs interacting and regulating each other on different timescales. Living beings are constantly renewing themselves, and living planets may do the same. Our skin seems permanent, but no cell lasts more than 2 weeks. Our bones seem solid but are always being deposited and re-absorbed, like an active planetary surface. So, just maybe, this is what's really required for life. Maybe a planet that is geologically "alive" is more likely to be biologically alive. Maybe, a living planet will always "look alive", in the sense that the Earth does, with a constantly self-renewing surface and atmosphere.

Venus has an active surface and interior and a lively atmosphere with complex chemical cycles that perpetuate gradients of matter and energy. In theory, this kind of disequilibrium environment could feed a steady supply of nutrients and energy to any creatures crafty enough to evolve in the Venusian environment.

Of course there is a serious objection to this. Neither organic (carbon) compounds nor liquid water can exist at the temperature of the Venusian surface. But how sure can we be that this rules out life?

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Love That Dirty Water

"The universe is not only queerer than we imagine, but it is queerer than we can imagine" --J.B.S. Haldane

First let me say that I am a big fan of carbon-based life. Some of my best friends are carbon-based. Carbon and water are two substances that each have incredible properties on their own. In combination they do something completely different, something that neither could do on its own. Carbon, with some oxygen, nitrogen and a few other elements mixed in serves as the universal template, the flexible yet solid Lego blocks of life that can build up an endless variety of huge and complex molecules. Water is the universal solvent. Dissolved in water, carbon molecules are free to flop around, twist themselves into complex shapes and interact with one another in the intricate dance that we call life. Something magical and creative beyond belief happened here as a result of carbon and water. Once it started it never stopped and it completely re-made our world. Carbon in water crawls and flies, respirates and synthesizes, colonizes, adapts, seeks and hides, gives birth, invents, worries, wonders and sings. If that's not magic, then what is?

Furthermore carbon-based life may be common in our universe. Both carbon and water are abundant everywhere we look, even out to distant galaxies. We have found carbon molecules, often mixed with water ice in comets, asteroids, meteorites, and even interstellar dust. Experiments have shown that at least the preliminary chemical steps of life might be commonplace wherever carbon and water meet. By contrast, the prospects for other kinds of life are dim--or at least uncertain--or such is the view from here--from this planet, so shaped by our kind of life, and also from inside our carbon based brains as we look out through our carbon-based eyes.

Science strives for objectivity and uses controlled, blind and repeatable experiments to remove the bias of the investigator. However, in the study of life we are the phenomenon under investigation. This makes objectivity difficult or impossible. Thus we should be very humble in our conclusions. Arrogance and dogma, in particular in an area where objectivity is impossible, are the antithesis of science.¹²

Sometimes I wonder if we are capable of thinking objectively about carbon-in-water. Are we deeply carbon biased? Who can blame us if we are? (maybe a sulfuric slime-sloth could.) I am talking about a possible bias to our perceptions here which is definitely not "subconscious" in the normal sense of the word, because that implies that it is based on some ideas that reside somewhere in the mind. This bias may be built into the chemical structure of our every cell. Pre-conscious might be a better word.

Our doors of perception are made of carbon-in-water. We see the universe through carbon-tinted glasses. Our very mechanisms of thinking and seeing are constructed of these same materials. Our external and internal worlds have been shaped by four billion years of carbon evolution. Much of what we are used to sensing and we find interesting is defined by this chemistry. This is pure speculation, but maybe carbon determines the patterns we respond to, and the scales of structure and organization that we notice. Not just spatial scales, but temporal ones: we are tuned to phenomena that change at the pace of carbon chemistry. Are we missing anything as a result? True, our science has been steadily increasing the temporal and spatial range of our awareness, opening up the filters. But the filters are there. These are some of the carbon biases which I can imagine. Some of them probably don't apply at all. But what of the biases which we can't imagine?

How much does this limit, or define, what we see of the universe? Is our love of carbon (and our propensity to view the universe's potential fertility wholly in terms of carbon-based life) merely a bias based on our local experience, or is carbon really the only way to live? I have no idea. It's possible that this is inherently difficult for us to know. We have here an example of one world with life. That is not much to base a solid scientific conclusion on.

For another angle on this subject, consider the phenomenon of path dependence. Certain choices made in the past, possibly at random, become entrenched as the machinery evolves to facilitate and use an existing system. A great example is the QWERTY keyboard found on every computer.¹³ This layout doesn't make any sense for ease of typing. It came about due to the mechanical requirements of early "typewriter" design. Schemes to make typing easier have never gotten off the ground because this system is locked in: the cost of switching over is too high. You would have to change people's habits, change all keyboard manufacturing equipment, other equipment and software that interfaces with keyboard-driven machines, all the equipment used to manufacture that equipment and so forth.

Many of the specifics of our biological systems are path dependent. DNA is surely not the only molecule that living things could use to reproduce. Our protein-making machinery uses only 20 of the many possible amino acids. There is no obvious reason why these twenty are the best, but the system was perfected using these long ago. One feature of such a path-dependent evolution is that a system that has evolved to the point where it operates well, with efficiency and reliability, may seem like the best (or only) system even if it is only one of many possibilities, dependent on arbitrary choices made long ago which have since been codified and maximized.

It is obvious that this could be the case with some of the specifics of our finely tuned biochemistry. But how deep does this path-dependence go? Is it possible that some of the more basic choices our biochemistry has made, like the choice to go with carbon and water, could actually be path dependent? If we had started out with a different system, would it by now have evolved to the point where it works so well that it seems to us like the only one possible? "Geosphysiology" suggests that biological evolution always reworks its planet to optimize it for a growing biosphere. Maybe any sufficiently evolved chemical system will appear, to organisms evolved within it, as the only possible kind of biochemistry, at least when they first wake to consciousness and assess their situation in the cosmos.¹⁴

Carbon may need very special circumstances to come alive. In a wide range of conditions and locations carbon spontaneously forms the small modular units, like amino acids, that could be the building blocks of our kind of life. In the right conditions these units can assemble themselves into the large, complex organic molecules of "life as we know it". (like proteins, which are long chains made of thousands of amino acids) But, those "right conditions" define a much more narrow set of requirements. Carbon probably needs liquid water. It probably also needs a certain pH range (neither too acidic nor too basic), and some protection from the ultraviolet radiation which is ubiquitous in the universe. Most places carbon does not have "the right stuff", does not behave in such a way as to be conducive to life. As far as we know it's only in the unique liquid water environment of the Earth that these little bits of carbon get together and make life. This is why our thoughts about searching for life on other worlds are so focused on looking for other planets with liquid water.

If we lived in another environment, would carbon seem so special to us? If we lived on Venus, we might not even know about organic chemistry. Carbon would be something that exists as an oxidized gas (CO or CO₂) at room temperature and does not form stable complex molecules. Maybe we would learn about carbon molecules in the interstellar medium, on comets, or on Earth. Maybe we would notice a pervasive green pigment on Earth that seems to involve carbon chemistry. We might call it the "unknown absorber".

The temperature range of liquid water informs our intuitive sense of what is too hot, what is too cold, and what is just right for life. The properties of complex chemicals like proteins and DNA are highly sensitive to their external environment. That is why "life as we know it" has such a narrow comfort range. Heat us up just a bit and we cook; our proteins "denature", falling apart into their constituent amino acids. Cool us down a bit too much and we freeze, our cells turning to ice crystals that shred our cell walls. The realm of water defines terrestrial life's ultimate boundaries. Is it the same in the universe at large? Does life always need a watering hole?

Or does the universe have other ways to solve this problem? Could it be that by only seriously considering carbon-based life we are blinding ourselves to much of the universe's true biological potential?

One of the lessons we are learning from our recent explorations of Venus is that nature is not likely to do exactly the same thing twice in the evolution of complex planets. Could it be the same with the evolution of complex life?

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We are still trying to learn how biochemistry works here on Earth. We do not know nearly enough to have figured it all out from the basic laws of physics and chemistry. It's no accident that chemistry is a metaphor for unpredictable human interactions: in the same way, we don't know nearly enough to be able to predict what the outcome of all possible chemical combinations will be, although we are getting better at it in some cases. If we ever did perfect this art (or science) there would be no need for experimental chemistry.

We are still clueless about many details of the workings of our own bodies, but we know carbon chemistry fairly well because we are naturally curious about it, and there are huge economic incentives to study it. What other element can claim to be the basis of several academic disciplines (organic chemistry, biochemistry) and numerous multinational corporations (Sandoz, Genentech)? Who knows what potential, what lurking complexity, what surprises we would find if we turned the macroscope of our intellect with such sustained and focused intensity on any other corner of the periodic table?

These days many people are trying to save Earth's rain forests from destruction. This is important not only because of their role as a contributor to the global atmospheric balance and a habitat for life, and not just because of their sheer priceless beauty, but also because of the vast and largely untapped chemical creativity in the forest species. We are still finding substances with significant pharmaceutical potential that we haven't the foggiest how to invent or manufacture. Time and again, even in the familiar environs of Earth, we find that "dumb" nature is so much smarter and more resourceful than we are. How can we put narrow limits on its creativity elsewhere in the universe? Nature always surprises us. Why shouldn't this be true on the level of planetary environments and chemistry for life? If the universe wants to be alive badly enough, it will find a way. Nature will find the hidden pockets of order, nurture them, and shape them into biospheres which grow into and with their worlds, transforming them into magic kingdoms like, but unlike, our own. To assume that carbon-in-water life is the only kind possible could be like our historical assumption that Earth was the only world.

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If we relax this criterion, then the ban against life on Venus is less certain. Everyone seems to be convinced that it is completely obvious there is no life there, but several new developments have made me re-think this--some new ideas about Venus and some new ideas about life. Venus may have some of the general properties of a "living planet": a geologically active surface and a self-refreshing atmospheric and cloud system. Some scientists working on general theories about biological evolution believe there may be a tendency in the universe for self-organization, complexity and--just possibly --biology. This may or may not have specific chemical requirements.

Admittedly, this is a long shot, but I consider life on Venus to still be an open question. In any case, thinking about it is a worthwhile exercise that may help us to better understand the real limits of life.

This solar system is full of surprises. We keep finding familiar processes occurring in the strangest of places. Nobody expected to find "rivers" on the plains of Venus or "snow" on its high peaks. On Venus, sulfuric acid plays the role of forming clouds, just as carbon dioxide does on Mars and methane does on Titan. Other substances are condensing out on the mountain tops and sustaining long distance flows. These are all roles played by water on Earth.

Planetary evolution has certain recurring themes: phenomena and structures that are common on planets with widely different conditions. When the material that plays this role on Earth is unavailable or inappropriate, then something else takes its place. Different physical conditions allow different substances to step up to the plate and perform the same function. Could it be so with life?

In this view, the statement "Life can't exist on Venus because it's too hot." may be analogous to "It can't snow on Venus because it's too hot." If rivers can form on Venus without a drop of water, maybe some kind of cells and organisms could evolve, using stuff that we are not predisposed to think of in such a role. A living cell is much more complex than a river. Does that make it more or less likely that we would recognize or imagine the correct analogy?

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Venus might have been the best place of all for organic life to get started. Our sun has been heating up steadily over the 4.5 billion years of its existence. Sunlight was dimmer by about 40 percent when the sun and the planets were very young. This means that, depending on the details of atmospheric evolution, all of the terrestrial planets might have been a lot colder. Earth and Mars may have been too cold, and Venus "just right" for life of the water-borne variety. If life did form on Venus and spread to the other planets it must have emigrated quite early, since our ancestors were certainly here 3.8 billion years ago. On Mars the poor little buggers would eventually have been freeze-dried by subsequent global change, whereas on Venus they would have been broiled, unless they found a way to live in the cool clouds and eat acid.

We may have gotten started on Venus. If so, then our spacecraft are the first calling cards of a prodigal sister, returning home after living for billions of years on another world.

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By early October 1994 it was clear that the end was at hand. We had completed most mission goals, and funds were running dry. The spacecraft was losing power rapidly, its solar panels finally giving out after seeing Magellan through more than 15,000 orbits. Magellan could have been left circling around Venus, but its low orbit would have decayed eventually, and it would have met the same fate. Instead, it was done in by an "assisted suicide" that allowed us to perform one final experiment. On October 11, 1994, five-and-a-half years after it was launched from Earth, we fired thrusters to lower Magellan's orbit into the upper atmosphere. The wing-like solar panels were rotated to make a windmill shape, and we measured the increasing thickness of the upper atmosphere by watching how Magellan spun as it plunged. Magellan died as a kamikaze corkscrew for science, sending home new information until the end.

Our tracking stations lost Magellan's signal for the last time at three in the morning, California time, on October 12. We can pretty much guess what happened after that, as Magellan finally entered¹⁷ the world it had circled and scrutinized for years. The solar panels and large main antenna must have been torn off first. Then various smaller pieces would have started to rip off, some igniting in the growing heat from friction with the increasingly dense atmosphere. But Magellan entered fairly slowly and probably did not burn up entirely. The larger chunks probably fell to the surface, where they would have landed gently because of the dense atmosphere, like shells settling to the bottom of the sea. Judging from Magellan's location at the time of its final transmission, some pieces may have landed on the high peaks of Maxwell Montes. Maybe some day the Smithsonian will offer a prize for the first Magellan-part found and returned to Earth.

We have not yet thoroughly analyzed, much less understood, the huge wealth of data dumped on us by Magellan. It takes a while to digest a world's worth of images, re-evaluate our home world in light of the data deluge, and develop a new understanding of Earth-like planets. The big picture of Venusian evolution is still shrouded in clouds, now patchy and thinning in places, which will continue to be slowly dispersed by mature reflection.

We've learned a lot about Venus and we will learn a lot more by carefully studying our Magellan images over the decades to come. But we still need a lot of answers that we will have to go back to Venus and ask for.

******

We think of Venus as a bright, luminous planet, but if we went and spent some time on the surface, the light would seem dim and diffuse. It's relatively dark there for the same reason that the planet glows so brightly in the skies of Earth: most of the light is reflected back into space by the clouds. But there is plenty of light at the surface to see (like a deeply overcast day on Earth) and your eyes would quickly adjust. The most striking characteristic of the light would be its deep red cast, a permanent sunset color that results from scattering of light by layers of thick atmosphere and clouds. Looking up into that deep red sky, you might learn to judge the time of day by the slow movement of brightness across it, but you would never see the sun, and there would be no shadows (terrestrial vampires would feel at home).

I've said earlier that the sky is an unbroken, unchanging overcast. I was repeating what I've heard many times, which always seemed reasonable enough. But now I'm not so sure. Now we know how patchy the clouds are. As I described in chapter 3, recent discoveries in the near-infrared "windows" showed us that the bottom layer of clouds, where most of the cloud mass is and most of the light is blocked, is full of holes. Although we never saw them with earth-based telescopes or orbiting spacecraft not tuned to the right infrared channel, we now know that there are thin and thick patches of all shapes and sizes down there. On the night side, in the infrared, the places where the clouds are thin appear as "hot spots" from which the heat radiation shines out to space. (as seen in the Galileo picture on page N). On the day side, I suspect we would see these as brighter patches in the sky. On overcast days here on Earth we still see bright and dark patches of sky where the thickness of the clouds varies. I think we would see the same thing on Venus. The contrast between the "hot spots" and "cold spots" on the night side is huge--some places are 10 times as bright as others. Some of the spots are hundreds of miles across. I think the biggest and brightest patches could be seen from the ground. If so, the sky of Venus becomes a lot more interesting because it would be constantly changing.

Furthermore, the superrotation of the upper atmosphere would be rendered visible from the ground. These cloud patches would move a thousand miles from eastern to western horizon in about 5 hours. What a sight that might be: giant shifting shapes of light and darkness slowly forming and dissolving as they traversed the sky 30 miles overhead. You might sense subtle changes in the light around you as large thick and thin patches of cloud passed by above. Standing on the ground, the air around you would be very still, perhaps broken occasionally by a very light gust of searing wind. But glancing upwards you would see a constant reminder of the raging winds that circle the planet.

That's the daytime. At night, things could be considerably stranger. At midnight the sky is completely dark, and the main source of illumination is the glowing of the red-hot ground! The surface is so hot (almost 900o) that its thermal radiation would produce a faint red glow. The darkness might also occasionally be broken by a faint flash of lightning from high above in the clouds¹⁸.

It's not just the quality of the light but the pace of its changes that would tell you immediately that you are not in Kansas any more. On Earth, day and night last roughly 12 hours, depending on the season and your latitude. The terminator (the line between day and night¹⁹) sweeps across the landscape at 1000 miles per hour at the equator, and is slower at higher latitudes.²⁰

On Venus, day and night each last 59 Earth days, or about two Earth months. The terminator is a diffuse boundary that strolls from West to East at a leisurely 8 miles per hour at the equator. At a high latitude, say Maxwell Montes at 70oN, it would move at 3 miles per hour. So if you stayed in one place you would have to wait a very long time for the light to change, but it might be worth the wait. As twilight approached, the sky would very slowly dim and the glow of the ground would become noticeable. Maybe it would feel like those enchanted times on Earth when the landscape is illuminated by a slowly shifting balance of full moonlight and fading twilight. Dawn would bring a similar slow changing of the guard from ground-glow to sky-glow.

This leisurely pace of change could have its advantages. On Earth, if you are traveling in a jet aircraft, you can play tricks with the time of day. Traveling westward at the right speed, you can make sunset last for a very long time. Traveling eastward, the night passes quickly. On Venus the changing of the light is so slow that you could do these things on foot! Remember how St. Exupery's Little Prince kept moving his chair around his asteroid to watch the sunset over and over again? Similarly, if you had a favorite time of day on Venus, where the light was perfectly balanced between ground and sky, you wouldn't have to wait for night to fall. You could just walk there.

Some of the most interesting places to be on Venus, in terms of the quality of the changing light, might be near the north and south poles. Here you might find a perpetual twilight, a balance between the constant ground-glow and the sky-glow that SLOWLY travels around the horizon, as Venus spins.

Because its spin-axis is not tilted like Earth's, Venus has no seasons, but the changing time of day there has the pace of seasonal change here. A month-long afternoon is followed by several weeks of twilight before night fully falls. All of this refers to changes in illumination, not temperature. If you become overheated during a long, Venusian afternoon, and you want to cool off, don't bother to wait for dark. Not only is it a long wait, but the temperature doesn't change. Going north or south to the poles won't help either. The thick atmosphere of Venus redistributes heat so that time of day and latitude have no effect on surface temperature. If you want instant heat relief, climb a mountain.²¹ Everywhere on Venus, it gets about 5 degrees cooler for every thousand feet of altitude. The high peaks of Maxwell, towering 38,000 feet above the plains, are a cool 710 degrees in the shade.

Walking on Venus might be easier than on any other planet, if we could design a survival suit that was not too cumbersome. Remember the images of Apollo astronauts stumbling and bumbling around the lunar landscape, occasionally falling and taking expensive pieces of equipment with them? They had to devise a whole new way of walking, or hopping, to get around in the Moon's low gravity, which is 1/6 Earth's. Our way of getting around on our planet is deeply tied to its gravity. But your weight on Venus would be only 10 per cent less than here, so you would not need a new way of walking. In fact, this would give you an added lift, an extra spring in your step, without really throwing you off.

As for what its like at different locations, there are probably as many answers as there are places. Personally, I would love to stand on the banks of one of the rock-rivers and see if it really looks like a river on Earth, or hike up the side of a shield volcano, searching for a bubbling lava lake. We won't really know what it's like there until we go and find out.

******

Oh We, Like Cats

"One of these days these boots are gonna walk all over you." -- Nancy Sinatra

But will we go? We've sent our machines there, and will continue to do so. But will humans ever walk on Venus? Human exploration of space has slowed to a crawl. This seems to be part of a larger collective lack of nerve, a wave of self-doubt and fear of the future that we are experiencing as we approach the millennium. We are wondering what we have done to ourselves, other species, and our world. We are struggling with our addiction to high technology: we need it, we love it, and yet we have not completely learned how to live with it in a non self-destructive way.

Maybe we need to slow down, catch our breath, and get our own house in order before heading out into space again. After all, look what happened the last time. We went to the moon without really knowing what we were doing or why we were doing it, and it didn't stick. We then retreated so thoroughly that we can't even get back there today. Apollo was quite an achievement, but when we send people to Mars or even eventually to Venus, it would be better to have a clear, long-term plan.

I have a fantasy of cloud-cities on Venus, huge enclosed habitats suspended from giant balloons. At a certain altitude where the temperature and pressure would be comfortable for us, we would mostly just have to keep the air fresh, maybe by collecting solar energy to make oxygen from CO₂, or better yet, growing plants to do the job for us. Why should we bother to do such a thing? I don't know. These could be research stations, or maybe there will be some economic incentive, something rare or beautiful found only on Venus. Or maybe, in the very long run after we have solved all our major problems here on Earth, we will go just for the hell of it, because it is there. (Yes, now I really am fantasizing.)

Anyway, it doesn't really matter what I say here, or anyone else writes in any book. Generations from now, I think, we will explore the clouds and the surface of Venus in person. I can't think of a rational reason to go, but we humans will always keep exploring, perhaps because it is our destiny, or because we can't resist knowing what lies beyond that closed door. If you have ever lived with cats, you know that they will get into anything new or mysterious that appears in the house. Any unexplored frontier compels them. They will keep trying until they get inside. Humans are a lot like cats, so curious that we must poke our heads everywhere, look around every corner, under every curtain and behind every door, even when it might get us into trouble. We will continue to explore the universe for the same reason cats explore closets. Like cats, we also sometimes have more impulsive curiosity than foresight. It's easy and fun to climb up the tree, but now how you gonna get back down? (Where you gonna bury that nuclear waste?) But we are capable of learning. You know what curiosity did to the cat, but we are a bit smarter.²² I know that's not saying much, but if our curiosity is augmented with wisdom, if we integrate what we find along the way into a new, larger and longer perspective, I think we will go far.

******

Terraforming and Veneraforming

	"Earth First! We'll mine the other planets later." -- bumper sticker seen outside Telluride, Colorado
	"The mutation from terrestrial to interstellar life must be made, because the womb planet itself is going to blow up within a few billion years . . . Planet Earth is a stepping stone on our time-trip through the galaxy. Life has to get its seed-self off the planet to survive." --Timothy Leary

Venus today may not seem like a place where anyone in her or his right mind would ever want to go. Could we re-make it in Earth's image? This idea is as tantalizing in some ways as it is horrifying in others.

Various schemes have been dreamed-up about how we might one day alter the environments of other planets to be more like Earth, so that we could go live on them without needing suits or domes. This is called "terraforming." Most schemes focus on Mars because it already has the most Earth-like surface conditions and so would need the least work.²³ These plans are somewhat cartoon-like: "All we have to do is add 20 zillion tons of oxygen and then plant some geraniums." They tend to focus on what is needed for life and ignore hazards that may be present. For instance, if we created a warm, oxygen atmosphere on Mars, what poisonous trace gasses might also be there, oozing out of the rocks? All of the schemes are fantastically expensive and impossible given our current technology. The impossibility of doing these things, for now, absolves us from the responsibility of deciding whether we should.

On Venus, the major impediments to our comfort are the temperature, the pressure, the unbreathable CO₂ atmosphere, and the lack of water (otherwise it's quite nice!). Terraforming schemes all focus on getting rid of large amounts of CO₂ and converting some of it to oxygen. This would solve three out of four problems. Then, just add water and voila! There is another problem that some of the schemers and dreamers do not consider: if Venus had Earth's atmosphere but retained its very slow rotation, daytime heat and nighttime cold might be unbearable. It's hard to say what kind of weather would result. So, while we are scheming, we should also figure out how to spin Venus up to a more "normal" rotation rate.

In brief, here are four ideas proposed to "fix" Venus to be more like Earth:

These schemes may all seem a bit fantastic, silly even. Each of them has been discussed in much more elaborate terms, with detailed calculations of the energies and timescales involved. This doesn't make any of them sound a lot more credible though. The least offensive and the most doable is the last one. Biological solutions do not take huge amounts of energy because they use the natural, exponentially multiplying quality of life. If we found or created a suitable organism, we would only need to introduce a small amount and it would eventually spread and transform the planet.

One more possibility is worth mentioning. In chapter 5 I pointed out that some new evolutionary climate models hint at instability in the climate of Venus, or at least the potential for instability that we might be able to trigger. If so, we might use a minor application of any of the above schemes to jump-start a runaway cooling. Cool things down just a little , and surface-atmosphere chemical reactions might remove CO₂ from the atmosphere, reducing the greenhouse effect and cooling things still further. The resulting feedback loop would cause the climate to decay to a condition we would find more comfortable.

These schemes seem impossible and perhaps unethical, so why even bother to discuss them? Well, today's impossibility is tomorrow's engineering project. Who would have thought, 100 years ago, that we would have walked on the moon (and then abandoned it!) by now? The dreamers are sometimes the advance wave of the next revolution. But there is a much better reason to be talking about this now. Thinking about terraforming is good intellectual sport. It's fun, and it stretches our mind-muscles in useful ways. Fantasizing about how we would terraform other planets helps us think about how planets and climates work and how they might change. Thinking about changing planets in a purposeful way is especially good for us, because we have been changing our own planet in random, haphazard ways. We need to learn how to take a more collective, constructive approach to altering our planet's environment. By imagining how we could do this elsewhere, we enlarge our understanding of global change. Any successful terraforming project would take generations to complete. It's good for us to practice thinking about global change on such long timescales. In fact, our survival will depend on our learning how to do this. The value of thinking about terraforming is that it can help us learn how to stop veneraforming our own planet! (making it more like Venus.²⁴)

Understandably, talk of monkeying around with planets makes many people uncomfortable. There is a natural resistance to such ideas, given our sorry recent history of tinkering with this world beyond our ability to foresee, or cope with, the consequences. There is a strong reaction against the human arrogance of thinking we can "play god" with the solar system when we seem to be barely able to manage our affairs down here. We do have a history of charging off and "exploring" places in an intrusive and impulsive way, messing things up, then realizing it later and issuing half-hearted apologies. We must learn from this, and step mindfully into the Solar System. At the very least, we should hold ourselves to the standard of being able to consciously terraform Earth (rather than unconsciously veneraforming it as we are doing now) before we take on other worlds.

Finally, there is a further moral dimension: Do we know for sure there is not extant life on Venus or Mars that we would be destroying? We must be much more certain about this than we are now before we risk, in our ignorance, wiping out a biosphere.

Even so, we may one day decide that it is a good idea to transform other worlds. If we ever determine, for sure, that, say, Mars is utterly lifeless (something not possible with our current scientific abilities) then the ethical imperative changes. Propagating life is arguably a good thing, and preserving life is certainly a good thing. If we want to insure that Earth life, including humans and other creatures, survives the planetary disaster that surely will come some day (by asteroid, comet, human stupidity or something unanticipated), we must gain permanent outposts beyond Earth. Mars and Venus may eventually be options for this kind of trans-planetary life insurance policy.

We are community, within and without.²⁵ It's only natural to want to extend this and create an interplanetary community. There is beauty and inspiration in the vision of humanity's spreading into the galaxy, leaving the cradle, becoming who-knows-what. Throughout my teenage years, this was one of the guiding visions of my life. I have since gained a healthy respect for our current limitations. I still believe in the vision, but I think we have some major tests to pass first. We have to do our homework before we can graduate to being a wise, space-faring species. To survive, thrive and possibly expand, we must learn some of the lessons Earth is trying to teach us right now--lessons about our limits and our interconnectedness, lessons about what it means to function and live sustainably as part of a planetary community.

Fortunately, it will be a long time before we are capable of terraforming, so we can mull over the ethical implications for at least a century and perhaps several. Maybe we will decide that it is not such a good idea. Terraforming will remain a purely intellectual exercise for the foreseeable future and, as such it is fun, and arguably worthwhile to fantasize about. But if anyone suggests seriously that we embark on any of these schemes any time soon, they should be institutionalized, or forced to teach Freshman Astronomy at a large public university. Any actual plan to implement such changes would be the height of folly until we learn a lot more about life, about planets, and about ourselves.

Footnotes:

¹ Complex molecules dominated by carbon.

² Or maybe it will just be given an icy reception. Equally appropriate.

³ Fortunately for him, I don't think Vernadsky lived to see the advent of the modern mall. He died in 1945.

⁴ See chapter 4 for a discussion of the meaning of equilibrium.

⁵ The total entropy of the solar system increases every day, mostly because the sun increases its entropy as it radiates energy.

⁶ Recall the example of a gradient of salinity across the zone where rivers of fresh water flow into, and mix with, the salty sea.

⁷ There is nothing inherently colorful about these patterns. They are just collections of numbers being represented with an arbitrary color scheme.

⁸ Some non-living natural processes make fractals, too, most notably erosive structures, like branching rivers. It is interesting that these forms usually involve some of the same conditions that make life arise, like flowing water. Is this a coincidence?

⁹ I love this kind of prediction. I can only be proven right or wrong by a fantastic discovery.

¹⁰ What do I win if I'm right?

¹¹ Some have said that complexity implies that we are "expected". I like "implicit" better than "expected", which implies that someone has been expecting us.

¹² Such arrogance certainly will not win science many fans. Scientists often complain about the proliferation of pseudoscience, mysticism and superstition and decry the lack of faith in the scientific method. If we added more humility, and appreciation of the unknown and unknowable to our scientific education it could go a long way towards helping us compete in the world-view marketplace.

¹³ This has its origins in an antique machine called the "typewriter".

¹⁴ Is it possible that our expectation of finding life that is chemically just like us, on a planet similar to ours will seem, from some future vantage point, as quaintly naive and amusing as Star Trek aliens who all look like humans with minor anti-cosmetic surgery?

¹⁵ One of these Martian meteorites, Nakhla, actually struck and killed a most unlucky dog when it fell in Egypt in 1911. There are probably Venusian meteorites too, but we haven't identified any yet.

¹⁶ I really want to say, "him", that's what happened to "HIM!" This feels like talking about the death of a friend, not just a machine. But, I don't want to get into that whole pronoun business again.

¹⁷ This has been called Magellan's atmospheric "re-entry", but that doesn't seem quite the right term for a spacecraft launched from another world.

¹⁸ We are still not sure whether there is lightning on Venus. We've recorded some suggestive electrical pulses, but we have yet to observe the telltale flash.

¹⁹ Not a beefy robot sent from the future.

²⁰ You multiply this by the cosine of your latitude, so that at 45^o it moves at about 700 mph. It also changes with the seasons.

²¹ Summer time in Tucson, where I lived for 7 years during grad school, is pretty much like Venus, always hot in the desert, day and night, always cool up in the mountains.

²² If physically somewhat less resilient, and each possessed of 8 fewer lives...

²³ This may seem far out to you, but hey, Las Vegas and Tucson have been terraformed, at least temporarily, so anything is possible.

²⁴ See "Venus Envy" in chapter four.

²⁵ That is, our bodies are, in a sense, communities of microorganisms, and our biosphere is an intricate mesh of interacting communities.