The most likely culprits are so-called Earth-crossing asteroids— objects with highly elliptical orbits that cross the plane of Earth’s more circular path around the Sun. At least three hundred of these potential killers are known, and in the next few decades some of them will pass uncomfortably close. On February 22, 1995, a just-discovered asteroid with the benign name 1995 CR whizzed by within a few Earth-Moon distances. On September 29, 2004, asteroid Toutatis, an elongated 1.5-by-3-mile object, passed even closer. And in 2029 asteroid Apophis, a 900-foot diameter rock, is predicted to cross much closer still, well inside the Moon’s orbit. That unsettling encounter will irrevocably alter the Apophis orbit and possibly bring it even closer in the future.

For every known Earth-crossing asteroid, there are probably a dozen or more yet to be spotted. And when one of these projectiles is finally observed, it will likely be much too close for us to do much about it. If we’re the bull’s-eye, we may only have a few days’ warning to settle our affairs.

The consequences of an impact will vary according to the size and location of the impact. A ten-mile boulder would devastate the globe just about anywhere it hits. (By contrast, the dinosaur-killing asteroid of 65 million years ago is estimated to have been about six miles across.) If a ten-mile object hits the oceans—a 70 percent chance, given the distribution of land and sea—then all but Earth’s highest mountain peaks will be swept clean by immense globe-destroying waves. Nothing will survive up to a few thousand feet above sea level. Every coastal city will utterly disappear.

If such a ten-mile asteroid hits land, the immediate devastation may be more localized. Everything within a thousand miles would be obliterated, and massive fires would sweep across whatever continent is the unlucky target. For a short time, more distant lands might be spared the violence, but such an impact would vaporize immense quantities of rock and soil, sending Sun-obscuring clouds into the high atmosphere for a year or more. Photosynthesis would all but shut down. Plant life would be devastated and the food chain would collapse. A few humans might survive the horror, but civilization as we know it would be destroyed.

Smaller impactors would cause less death and destruction, but any asteroid over a few hundred feet, whether it smacks the land or the sea, would cause a natural disaster greater than anything we have known. What to do? Should we ignore the threat as too remote, too insignificant in a world that has so many more immediately pressing problems? What could we do to divert a big rock?

The simplest, first step in avoiding such an event is to look as hard as we can for those elusive Earth-crossing destroyers—to know the enemy. We need dedicated telescopes, automated with digital processors, to locate the Earth-crossing projectiles, to plot their orbits and predict their future pathways. Such an endeavor is relatively cheap and already under way. More could be done, but at least the effort is being made.

And what if we found a large rock that is projected to smash into us a few years from now? For the late Carl Sagan, along with others in both the scientific and the military communities, asteroid deflection is an obvious strategy. If initiated early enough, even a small nudge by a rocket engine or a few well-placed nuclear explosions could shift an asteroid’s orbit sufficiently to change a collision course to a near-miss. Such an eventual necessity is reason enough for a robust program of space exploration, he argued. In a prescient 1993 essay, Sagan wrote, “Since hazards from asteroids and comets must apply to inhabited planets all over the Galaxy, if there are such, intelligent beings everywhere will have to unify their home worlds politically, leave their planets, and move to small nearby worlds around. Their eventual choice, as ours, is spaceflight or extinction.”

Spaceflight or extinction. To survive in the long run, we must journey outward to colonize neighboring worlds. First will come bases on the Moon, though our luminous satellite will long remain a hostile place to live and work. Next is Mars, where more abundant resources— especially lots of frozen subsurface water, but also sunlight, minerals, and a tenuous atmosphere—are at hand. It won’t be easy or cheap; nor is Mars destined to become a thriving colony anytime soon. But settling, and perhaps terra-forming, our promising neighbor may well be the next essential step in our species’s evolution.

Two obvious obstacles will probably delay, if not prevent, the establishment of a Mars base. The first is money. The many tens of billions of dollars it will take to design and implement a Mars landing is outside the most optimistic NASA budget, even in the best of financial times. A cooperative global effort may be the only option, but such a massive international program has never been attempted.

Astronaut survival is an equally daunting challenge, for it’s next to impossible to ensure a safe round-trip to Mars. Space is harsh, with myriad sand-size meteorite bullets to pierce the thin shell of even the most armored capsule and unpredictable solar bursts of lethal penetrating radiation.

What’s more, no rocket technology on the books would allow a spaceship to carry enough fuel to get to Mars and make it back. Some inventors talk of processing Martian water to synthesize enough fuel to refill the tanks, but that technology is only a dream and probably a long way off. Perhaps the more logical option—one that flies in the face of NASA mores but is increasingly promoted in passionate editorials—is a one-way trip. Were we to send an expedition with years of supplies instead of fuel, with sturdy shelter and a greenhouse, with seeds, with a lot of oxygen and water, and with tools to extract more life-giving resources from the red planet, then an expedition might just make it.

Fifty million years from now, Earth will still be a vibrant living world, its blue oceans and green continents shifted but recognizable. The fate of our human species is much less certain. Perhaps we will be extinct. But it is also possible that humans will survive and evolve, moving outward to colonize first our neighboring planets, then our neighboring stars. If so, if our descendants make it into space, then Earth will surely be treasured as never before—as a preserve, as a museum, as a shrine and place of pilgrimage. Perhaps only by leaving our world will humans ever fully appreciate the place of our species’s birth.

Reprinted by arrangement with Viking, a member of Penguin Group (USA) Inc., from The Story of Earth by Robert M. Hazen. Copyright (c) 2012 by Robert M. Hazen

Life is extremely resilient once it takes hold, but it requires rich chemistry, large energy sources, and stability, right from the beginning. The comparative planetology of our Solar System makes it seem like those initial conditions are hard to come by. Earth seems perfect, whereas the rest have obvious defects. Mars is on the smallish side, lacks a substantial atmosphere and water, and is very cold (although we still hope to find life there). Jupiter is too big; its crushing pressures and element-poor environment make interesting chemistry impossible. The trouble with such a comparative analysis, however, is that it leaves out a crucial class of planets that, purely by happenstance, doesn’t occur in our Solar System.

A super-Earth is a planet that is more massive and larger than Earth, although still made of rocks — perhaps with continents and oceans — and an atmosphere. There is no such planet in our Solar System, but we know that they must be common in other planetary systems. Moreover, theory predicts that they might have all the nice attributes of Earth, and, in fact, provide a more stable environment on their surface. True super-Earths!

A super-Earth is a planet defined by its mass — between 1 and 10 ME (where ME stands for Earth mass). The Earth’s mass is 6,310₂₄ kg, or a 6 with 24 zeros. That’s pretty big, but the Sun’s mass is 2,310_₃₀ kg — a million times larger — lest we lose perspective.

The first super-Earth was found by the serendipitous work of Eugenio Rivera, Jack Lissauer, and the California-Carnegie team in 2005. It orbits the small star Gliese 876 and is about seven times more massive than Earth. It is also very hot because it orbits very close to its star — only seven stellar radii, or approximately 1.7 million kilometers, away! (For comparison, this is only 3 percent of the distance from our Sun to Mercury.) Another, much colder super-Earth that is about 5 ME was discovered by J. P. Beaulieu and his team at the Paris Institute of Astrophysics.

In early 2007, Michel Mayor’s team in Geneva spotted at least three planets orbiting the star Gliese 581; two of them are super-Earths with minimum possible mass of 5 and 8 ME each, and orbital distances that are 7 percent and 25 percent of the distance from Earth to the Sun, respectively. A year later the same team reported several more super-Earths, some orbiting stars as big and hot as our Sun. The first transiting super-Earth was discovered by the CoRoT space mission in 2009: CoRoT-7b, a very hot small planet, probably similar to Gliese 876.

The preplanet structure — the “seed” of a planet — consists of solids (mostly silicates) and volatiles (such as water and ammonia), with trace amounts of hydrogen and noble gases. Due to the energy of the accretion process and the constant collisions with large solid bodies, this seed is thoroughly molten. (Some of Earth’s internal heat is a relic of this process.) In this state the structure differentiates. Iron and siderophile elements (high-density transition metals that like to bond with iron) precipitate from the silicate mix and sink under their own weight to form the core in the center. The remaining silicate minerals will remain in a mantle with the less dense ones closer to the top. Volatiles that are left over after hydrating the mantle minerals will rise to the surface and atmosphere.

Differentiation is an orderly and predictable process thanks to our knowledge of chemistry and mineral properties under pressure. Some super-Earths, the rocky ones, develop quite similarly, although the pressure in the mantle is almost tenfold higher and different varieties of minerals form. Other super-Earths, the oceanic ones, are totally exotic beasts, with oceans that are 100 kilometers deep overlying a dense hot solid water, called ice VII.

It might seem ridiculous to refer to this water as ice, given that it is at a searing temperature of 1,000 K, but under such high pressures, it forms. Water — H2O — has a familiar structure and formula, but our familiarity with it can make us overlook the fact that it is actually very complex. In common ice, the weak bonds between the molecules cause the molecules to form rings (mostly hexagons) that leave lots of empty space in between. The empty space gives it a lower density than liquid water, and so — as you know from a glass of ice water — it floats. Under high pressure the density of water increases as the molecules are forced closer together; the bonds are bent to form tighter rings, which also interpenetrate. That makes the water solid, almost irrespective of the temperature, and much denser than the liquid phase. The high-pressure ices that exist at high temperatures are known as ice VII, X, and XI; these are the ice phases we expect to find inside oceanic super-Earths. These ices are still less dense than rocks, however, so an oceanic super-Earth will be less dense than a rocky one of the same mass.

Ocean planets might be very common in the Universe because water is very common in the low-temperature environments where planets form and evolve. This might be especially true for super-Earths, which can retain volatiles more easily thanks to their larger mass and surface gravity. In order for a planet to become an ocean planet, it should form with or obtain at least 10 percent of its mass in water. Ammonia could be mixed in, but water is by far the dominant volatile chemical we see among the materials in proto-planetary disks. For comparison, Earth’s oceans are just about 0.02 percent of its mass.

An ocean planet, regardless of its surface temperature, should have the same layers inside: an iron core surrounded by a silicate-rich mantle that transitions into the hot water ice. The latter will become liquid water near the surface (the last 100 kilometers or so). The surface of the liquid water ocean will be covered with ice Ih, if the planet is far from its star and cold, like Jupiter’s moon Europa. If the planet is close to its star and hot at the surface, the liquid ocean will transition into a thick hot steam atmosphere. If the planet has moderate temperatures such as we have on Earth, the water ocean will resemble Earth’s, but there will be no continents or basalt tectonic plates under it. The interior of the ocean planet will remain under the control of the planet’s internal reservoir of heat. The transition between silicate mantle and hot water ice happens with a small change in density but no change in temperature, and the two materials have similarly high viscosity. Like the silicate mantle, the hot water ice “mantle” convects slowly.

The two families of super-Earths have planets that are diverse in size and amount of water. These characteristics depend on the mixture of elements present as the planet forms. From studying the spectra of many stars, we know that the amount of iron and other heavy elements will be different in different planetary systems. We already know that where in the proto-planetary disk a planet forms also matters. So, among the rocky planets we could find super-Mercurys — planets that have as much as 70 percent of iron core inside, like our planet Mercury. Or we could find super-Moons — planets that have no iron core, just an iron-rich mantle and perhaps a water layer.

There is a third possible family of super-Earths and terrestrial planets— carbon planets. These would be extremely rare, as they require more carbon than oxygen to be present in the planet-forming mixture. Normally carbon is half as abundant as oxygen. But astronomers have observed rare stars in which carbon is more plentiful than oxygen. A planet that forms from such a mixture will be different — it will have a mantle rich in silicon carbide and graphite in its interior. It will still have a precipitated iron core, but its overall size and the chemistry on its surface and crust will be very different. Silicon carbide is a very hardy substance — we use it to make durable ceramics, the disk brakes of sports cars, and tools for other high-stress environments. So volcanism, tectonics, and weathering are going to be minimal on carbon planets. Also, carbon planets are likely deficient in water.

Astronomy has always been about big numbers — astronomical numbers — and experience with big numbers has taught us that they do not guarantee inevitability. We have to go and find out for ourselves. Still, it seems likely that on some of those Earth-like planets, we will find signs of life. When we discover New Earth — a planet we could call home — the question of the “plurality of worlds” will come front and center, reminding us yet again that we are not the center of the universe.

Reprinted from “Life of Super-Earths: How the Hunt for Alien Worlds and Artificial Cells Will Revolutionize Life on Our Planet” by Dimitar Sasselov. Available from Basic Books, a member of the Perseus Books Group. Copyright © 2012.

In their new book, “Time Travel and Warp Drives,” Tufts physics professor Allen Everett and University of Central Connecticut math professor Thomas Roman explain the science behind the fiction of time travel, and tackle the question: Is it even possible? The authors delve into the lore of sci-fi shows and books to explain how wormholes, warp drives, and parallel universes work; and what Einstein’s theory of relativity is and its relevance to time travel. They also parse through all those pesky paradoxes that arise when one tries to go back in time.

Everett spoke with Salon over the phone to discuss how we perceive time, traveling at the speed of light, and why we can’t go back in time to kill Hitler.

I’m going to jump the gun and ask: In your opinion, is time travel possible?

There are ways in which it might be possible, but there are problems with all of those. I think it’s conceivable that time travel is possible. If someone put a gun to my head and made me make a yes or no prediction, I would predict no — with what we know now.

Twenty years ago, I think the answer would have been that it just wasn’t possible. We have learned some things about general relativity in the last 30 or 40 years or so, which make us take, at least for some of us in the profession, the idea of it being possible more seriously. But, still, one would have to say that the odds are against it. You might run into problems with time travel that you don’t run into with superluminal [faster than the speed of light] travel.

The correct statement is that backward time travel is not yet possible and may never be. We can travel forward in time.

How so, theoretically?

If you get into a space machine and travel from Earth to a nearby star and return, at a high speed (near the speed of light), when you get back to Earth, you will find that perhaps the trip took one year for you, as measured by your clock on the spaceship, but when you return to Earth, you will find that you returned to an Earth which is 10 years into the future, from the time when you left. So that’s exactly what we mean by traveling into the future. The possibility of doing that is well-established physics. As a practical matter it’s hard to do with people because the effect only becomes noticeable when the speed approaches the speed of light and it takes a prohibitive amount of energy to accelerate a people-carrying rocket ship to the speed of light and then slow it down again.

You can accelerate elementary particles (which decay radioactively to speeds very close to the speed of light). There are abundant observations to the fact that particles live longer when they are traveling at speeds close to the speed of light than they do when they are at rest. That is part of everyday observations in elementary particle laboratories. So you can certainly travel, in principle at least, into the future and return, but you can’t go back and listen to Mozart play a piano concerto. The chance of doing that is iffy at best.

You write that “it would be a bit tough to organize any kind of galactic federation” because of a phenomenon called “time dilation.” Can you explain what that is?

Suppose there’s a nearby galaxy which belongs to the emperor’s galactic empire. The emperor says, “I’m going to change the law in the empire. Henceforth, everyone on getting up in the morning must devote five minutes to praising the emperor.” So he sends one of his deputies off to a nearby star system with instructions to institute his new law, and in order to get there in a reasonable length of time, he’d have to be traveling at nearly the speed of light. He will get to the planet [in the nearby star system] in, let’s say, 100 years in the future, as far as the people on the planet are concerned. So they will say the law went into affect in the year [2111], but the Emperor’s deputy will take, say, only 10 years to travel to the planet, and another 10 years to travel back to Earth because of the time dilation effect. The law will be different at every point in the galactic empire because different observers will think the law went into effect at different times. I think that would make it difficult to run a reasonable empire.

Good point. So the person in the spaceship is experiencing time at a different rate?

Essentially, clocks in the spaceship are running more slowly than clocks that are at rest [outside the spaceship].

Does this have to do with our subjective experience of time?

No. If they don’t look outside, the people on the spaceship will not be aware that the time is moving slowly for them, but they will become aware of it when they return to Earth and find out that while 20 years has elapsed for them, 200 years has elapsed on Earth.

OK, if there are two different times, inside and outside time machine, then doesn’t time travel occur around us all the time? You mention in the book the idea of a bullet being fired. Theoretically, is the time inside the bullet slower than our time outside the bullet?

Yeah. If you imagine you had a tiny little watch in the bullet and you fired the bullet at a target, let’s say, 10 miles away. The bullet would take something like 10 seconds to get there, as seen by people on the Earth, but the little watch in the bullet, when it hits the target, will not read 10 seconds, but, say, 3 seconds. So the time as read by the clock in bullet will not be the same as the clock at the target, when the bullet get to the target — that’s provided you have synchronized the clocks.

[Going back to our previous example with the emperor], people on Earth and on the [other] planet think their clocks are running at the same rate, but then the clock on spaceship, when it arrives at the other planet, will not be synchronized with the clock on [that] planet because the clock in the spaceship (just as the clock in the bullet) has been traveling at high speed and has undergone time dilation.

A commonly repeated concern when speaking of time travel (to the past especially) is the danger of changing history. Is it possible to change the past? Can you get around the paradox of your travel being assumed (i.e., you are meant to go back but would you still be able to if your history is altered)? Is that when we run into problems?

Yes. That’s when you get into logical problems. You may go back in time trying to assassinate Hitler, but on the other hand you know that Hitler wasn’t assassinated. You cannot change the past. That past has already happened. Nothing you can do about it. If you travel back in time, the only possibility is if, somehow, you’re forced to do so in some way that doesn’t alter the past. Or, there is the other possibility that when you travel backward in time you wind up in a parallel universe. So in the universe we live in where Hitler wasn’t assassinated, we could, conceivably, travel backward in time into a different universe where you would assassinate Hitler and the subsequent time evolution in that second universe would then be quite different.

Can you explain what space-time is? We know time as the fourth dimension, but can we visualize it, spatially, like the three others?

In many ways, time is similar to the three dimensions of space but in other ways it is quite different. They are connected with one another, [but] there are important differences between them. A quantity in physics is defined by how you measure it. You measure the spatial difference between two points with a meter stick; you measure the temporal distance between them with a clock. That means, to a physicist, that they are fundamentally different quantities because the experiments that you did do to measure them are different.

Are there some fundamental truths or laws that must hold for time travel to be possible?

Among the most important laws of physics are the conservation laws, with things like energy and momentum, which must remain constant in time. As far as we know there is no way of producing or getting rid of the total amount of energy in the universe.

In Madeleine L’Engle’s “A Wrinkle in Time,” the characters travel by a method they call “tesseracting,” which involves folding space. Is time folding theoretically possible, in the way, say, we’re able to fold two- or three-dimensional objects?

Yes, if you can achieve the right distribution of matter and energy which would fold space in the manner you might like it to be folded. Whether you can really achieve that distribution of matter and energy is less clear. In particular, one of the things that is true is that if you want to fold space in such a way that time travel becomes possible, for example, you need a distribution of matter and energy with the property that there is a region of space and time where the energy density is negative—negative meaning that there is even less matter and energy present than the amount in empty space.

You talk about chaos or disorder in relation to backward time travel. Can you explain their relationship?

The question is: What is it that causes a difference between the two directions in time? The basic, classical laws of physics, which are Newton’s laws and their corresponding mechanical laws, make no distinction between the two directions in time—a process which can occur in one direction, can also occur in the opposite direction.

Why is backward time direction different than forward time direction? To me, the answer to that is something called the second law of thermodynamics, which says that the total entropy of the universe increases as time increases. Entropy is, essentially, the amount of confusion — mixing — in the universe. So, it’s that law which says it’s perfectly possible to see a diver dive off a diving board into a swimming pool. The laws of physics say that, if you arrange the system just right, in fact you can find that the diver will pop, spontaneously, out of the water and land on the diving board. It is possible, but the probability of the system having just the right conditions for that to happen is so small that we will never see it in the whole history of the universe. So when we talk about the difference between going forward and backward in time, what is it that defines that difference? Physicists say: What is it that produces an arrow of time? The answer is the second law of thermodynamics.

So this law explains cause and effect and why you can’t have an effect before its cause?

Yes.

Is it theoretically possible to get stuck in a time loop, like Bill Murray in “Groundhog Day”? 

The answer is yes, but you have to assume the “many worlds” interpretation of quantum mechanics is the correct one, and then you’re not exactly stuck in a time loop — every time you go around the loop, you come back to the same starting point in a parallel universe.

So, even if time travel is not possible for humans (for now), what do you think of its future prospects? And what kind of social impact does this kind of research bear on daily life?

Well, it’s hard to say because you don’t know what the results of the research are going to be. Physicists have learned quite a bit about the consequences of relativity as the result of this kind of research, so we know a lot more than we did, say, maybe 30 years ago. A person on the street might say, “So what?”—and that’s not an unreasonable attitude to have. Will there be actual consequences on people’s lives? It’s hard to answer that question. I would hope that the evolution of human society is going to be a lot different if it turns out that in some way or other, one can travel faster than light, in which case we would probably expand into the galaxy. From the point of view of humanity, I think the question of whether superluminal travel is possible will have a lot more consequence than the question of whether time travel is possible.

Salon spoke to Neubauer over the phone about the rise of the super-brain, his own religious beliefs and why outer space is almost certainly filled with life.

The book argues that books and cellphones and the Internet could be seen as part of our grander evolutionary strategy.

As I walk down the halls here, I see so many students typing away at their computers and everybody’s walking around with their little auxiliary brain. One brain is no longer sufficient and that is certainly the next step in terms of being able to master the forces that have impinged on us and be able to protect and expand humanity. Computers and the Internet now are in a sense creating a global brain where you can access information almost instantaneously and anyone has access to it.

In a sense, the Internet could be seen as the apex of human evolution.

The Internet provides us [evolutionary] mastery. It shows us how to build things, overcome disease, and allows us to maintain and buffer our way of life despite perturbations from the environment. We are a species now that can not only live on land but go onto the sea and go into space. We’re able to heat and cool our buildings at will in big cities where the lights never go out.

On the other hand, we’re losing the ability to have long-lasting human relationships and I don’t think everything is better necessarily through the union of technology and human behavior. We still need to confront each other face to face and talk about things to establish trust and work together. I don’t see technology as the solution to all of our problems.

At the end of the book you introduce an element that a lot of scientists or science writers would be unwilling to address: God. You argue that evolution and monotheistic religion are compatible. Why?

I should point out, that takes up about six pages in a book of about 275 pages. I am religious, I’m Jewish, and I find that being totally open to what modern science has to say does not interfere with my religious beliefs, and my particular bias is monotheism. I talk about [humanity] as an apex of nature and as a culmination of this high information pathway and that is compatible with the idea that personality was there at the beginning. I’m very far from this kind of Bible thumping that says therefore there must have been a garden of Eden and therefore the earth is 6,000 years old, etc. I’m trying to outline a way in which evolution is actually a friend of religion rather than it’s enemy. I think that is possible and that one can be totally open to what science is saying and still retain religious faith.

The numbers which allow our universe to exist are so improbable. There are about 14 different numbers which cannot be derived from fundamentals in physics, that allow this kind of universe to exist. It is also really orthodox at this point to say that there must be an infinity of universes and that there is a kind of eternal inflation taking place, that the entire cosmos is kind of like a glass of champagne that continuously has bubbles coming up in it.

I imagine that’s a very courageous stance to take in your field.

Well, thank you. It’s gotten me into trouble. It almost didn’t pass the board of Columbia [University Press] when they wanted to make a final decision about the book and luckily it made it through.

Back to the technological issue: If we see the Internet as part of  human evolution, that suggests that evolution is no longer a random event — and that we’re now in control of it. 

Randomness is clearly an important factor in what’s happening in nature. But the analogy I give is if you throw a rock down a mountainside, accidents will happen as it falls downwards — so each time you do it is likely to land in a different place. But you also can talk about the rock having an overall direction, and what I’m suggesting is that the way this universe was set up within the very first microsecond, there were parameters that gave it a destiny, and that destiny is working itself out through evolution over time. I shy away from the term “design” because I don’t think that everything is being controlled moment to moment — this is not God’s puppet show. The God that some people believe in has to come to the table and take a shot every once in a while to sink a ball, but the God I believe in took one shot at the beginning of the game and sank all the balls.

In the book you conclude that it’s very likely that life exists on other planets. Why?

Up until February of this year, astronomers had found about 500 planets outside our solar system, but now the United States has launched the Keppler Space telescope and after analyzing the data for about a half of the year, it has come up with another 1,500 prospective planets in an area that covers about 4 percent of the Milky Way.

Just by the law of probability, every star, no matter what its size, will have its habitable zone. That zone will be further out for a hot star and a cool one will have that zone closer in. If that is happening billions upon billions of times — the Milky Way is estimated to have about 2- to 3 hundred billion stars and there are estimated to be at least 80 billion galaxies in the universe — it’s just simple probability that what has happened in this solar system is very likely happening in many places across the universe.

But there also need to be building blocks for that life — lipids, amino acids and so forth. 

The scientific progress that’s been made in regard to the origin of life is just amazing. All of the components of cells have now been located through non-biological means. RNA can be synthesized in a non-biological way. Amino acids are widespread out there in interstellar space. Lipids are coming in on things like the Murchison meteorite. There’s a whole class of meteorites known as carbonaceous meteorites that have fractions of carbon in them.

Because of stars, there are very large quantities of carbon and oxygen out there. Take oxygen and combine it with the most abundant element in the universe, which is hydrogen, and it’s water — which is now believed to be the most abundant solid phase molecule across the entire universe. So if we have abundant amounts of carbon and water and these raw materials of cells then I would say that the chances are very high that this process is happening elsewhere.

On a more specific level, what does and doesn’t allow a planet to foster life?

There was a book about 10 years ago called “Rare Earth,” which argued that life was probably widespread in the universe but that complex life was not. But a more recent book, by J. Kasting, a scientist at NASA called “How to Find a Habitable Planet,” takes on a lot of these arguments and shows that there are just as strong arguments going the other way. If we look at life here on Earth it has an unbelievable toughness. We’re finding life in liquids as acidic as battery acid. We are finding life in boiling pools. When we drill in the Antarctic under large distances of ice, in places that are in eternal darkness, there’s plenty of life there and it’s not just simple life, they’ve come up with shrimp and fish that live under those conditions. In other words, it looks like life might be an accident waiting to happen.

So why haven’t we made contact yet?

As someone has suggested, perhaps they have seen the content of our TV programs and that’s precisely why they decided not to contact us, but Kasting, in his book, estimates that habitable worlds would be separated by about 250 light-years. That means if you say, “How are you?” you would need to wait 500 years for a reply that says, “Yes. I’m fine.” We may be underestimating the ease with which a universe that has life scattered all over the place is able to communicate.

The activists, most of them in their 30s and 40s, expected the climb to the top of the smokestack would take less than three hours. Instead, scaling a narrow metal ladder inside took nine. “It was the most physically exhausting thing I have ever done,” 35-year-old Ben Stewart said later. “It was like climbing through a huge radiator — the hottest, dirtiest place you could imagine.”

In the end, the fatigued, soot-covered climbers were only able to paint the word “Gordon” on the chimney before, facing dizzying heights, police helicopters, and a high court injunction, they were compelled to abandon the attempt and submit to arrest. They could hardly have known then that their botched attempt at signage would help transform British debate about fossil-fuel power plants — and that it would send tremors through an emerging global movement determined to use direct action to combat the depredations of climate change.

The case took on historic weight only after the Kingsnorth Six went to court, where they presented to a jury what is known in the United States as a “necessity” defense. This defense applies to situations in which a person violates a law to prevent a greater, imminent harm from occurring: for example, when someone breaks down a door to put out a fire in a burning building.

In the Kingsnorth case, world-renowned climate scientist James Hansen, director of the NASA Goddard Institute for Space Studies, flew to England to testify. According to the Guardian, he presented evidence that the Kingsnorth plant alone could be expected to cause sufficient global warming to prompt “the extinction of 400 species over its lifetime.” Citing a British government study showing that each ton of released carbon dioxide incurs $85 in future climate-change costs, the activists contended that shutting the plant down for the day had prevented $1.6 million in damages — a far greater harm to society than any rendered by their paint — and that their transgressions should therefore be excused.

What surprised both Greenpeace and the prosecution was that 12 ordinary Britons agreed. The jury returned with an acquittal, and the freed defendants made the front pages of newspapers throughout the country. The tumult also produced political results. In April, British energy and climate change minister Ed Miliband announced a reversal in governmental policy on power stations, declaring, “The era of new unabated coal has come to an end.” Discussing Kingsnorth, Daniel Mittler, a longtime environmental activist in Germany, told me recently, “it was probably one of the most impactful civil disobedience cases the world has ever seen, because it was the right action at the right time.”

If not now …

The idea that now is the right time for more resolute action to address the climate crisis is spreading fast enough to dot the global map with hot spots of disobedience. As it turns out, the Kingsnorth Six are part of a rapidly growing population. Joining them are the Dominion 11, arrested after forming a human blockade to stop the construction of a coal plant in Wise County, Va., in November 2008, and the Drax 29, who went on trial this summer for boarding and stopping a train delivering coal to a power plant in North Yorkshire, England, last year.

In fact, arrests are piling up quicker than journalists can coin name-and-number nicknames. The Coal Swarm Web site keeps track of an ever-lengthening list of protests. New headlines now appear weekly:

“Activists scale 20-story dragline at mountaintop removal site in Twilight, WV”

“14 Arrested at TVA headquarters in Knoxville, TN”

“10 activists board coal ship in Kent, England”

“Activists shut down Collie Power Station, Western Australia”

In August 2007, Al Gore, Nobel Prize-winning author of “An Inconvenient Truth,” told Nicholas Kristof of the New York Times, “I can’t understand why there aren’t rings of young people blocking bulldozers and preventing them from constructing coal-fired power plants.” By the time Gore made that statement, some young people had already started blocking bulldozers, and many more, young and old, would soon follow.

Still, Gore can be excused for feeling that such measures were overdue. With global warming, perhaps more than any other issue, there is a disjuncture between a widespread acknowledgment of the gravity of the situation we face and a social willingness to respond in any proportionate way.

The landmark 2007 report from the Intergovernmental Panel on Climate Change (IPCC) suggested that a two degree Celsius rise in average temperature, likely by 2050, would create severe water shortages for as many as 2 billion people and place between 20 percent to 30 percent of all plant and animal species at risk of extinction. It gets worse from there. An April 2009 Guardian poll reported: “Almost nine out of 10 climate scientists do not believe political efforts to restrict global warming to 2C will succeed.” More probable, they believe, is “an average rise of 4-5C by the end of this century,” a level that could create hundreds of millions of refugees fleeing areas afflicted by desertification, depleted food supplies, or coastal flooding.

That these consensus predictions may feel remote and improbable to much of the American public does not reflect a real scientific debate, but rather a common reluctance to face unpleasant facts — and also the considerable success of the coal and oil lobbies in dampening the electorate’s sense of urgency about the issue. Those two realities are precisely what direct action intends to confront.

An inconvenient politics

When Vice President Gore started endorsing civil disobedience, Abigail Singer, an activist with Rising Tide, a leading network of grass-roots climate groups, noted, “It’d be more powerful if he put his body where his mouth is.” She had a point.

As it happens, 68-year-old James Hansen, arguably the most famous climate scientist alive, has been less reticent about putting himself on the line. His involvement has furnished a great deal of mainstream respectability to those turning to more confrontational means of expressing dissent, and the trajectory of his political engagement catches an important trend.

Throughout the 1980s and 1990s, Hansen published many groundbreaking papers demonstrating the reality of a warming planet. Just as the work scientists had done in the early 1980s proving that human activity was creating a hole in the ozone layer had resulted in a 1987 treaty against chlorofluorocarbons, Hansen assumed that the work of those documenting climate change would result in swift legislative remedy.

“He’s very patient,” Hansen’s wife, Anniek, told Elizabeth Kolbert of the New Yorker. “And he just kept on working and publishing, thinking that someone would do something.” This time around, however, industrial interests proved far more entrenched. In order to help move glacially slow climate negotiations forward, Hansen started speaking out and, more recently, has begun risking arrest at demonstrations.

Of course, there is never a shortage of people who will question the tactics of civil disobedience and direct action. “We’re every bit as worried about climate change as the protestors,” a spokesperson for the E.On Corp., the energy company that runs Kingsnorth, said upon the announcement of the famous verdict, “but there are ways and means to protest and we would suggest their demonstration was not the way to do it.”

There are far less compromised skeptics, too. Many harbor a distaste for social-movement theatrics or operate on the belief that, sooner or later, science will speak loudly enough to force the political situation to sort itself out. Harvard University oceanographer James McCarthy expressed such a view when the IPCC released its 2007 report. “The worst stuff is not going to happen,” he said, “because we can’t be that stupid.”

Sadly, the latent hope that politicians will eventually come to their senses cannot suffice as a political strategy. The stark facts of segregation in the American South never put an end to that long-standing injustice; it took an unruly civil rights movement to force change. In this case, presumably less farsighted and more profit-hungry energy companies than the climate-concerned E.On have invested tens of millions of dollars in convincing elected officials and newspaper editorial boards that reducing emissions of greenhouse gases is neither practical nor particularly needed. The operative force at work here is not stupidity, but political power.

Hansen and others motivated to confront the industry head on have concluded that, unless there is a public counterbalance to the organized money of those who profit from the status quo, what science has to say will be largely irrelevant, no matter how theoretically convincing it may be. Unless citizens themselves become inconvenient, the truth will remain a minor consideration.

The disaster you can see

It is no accident that, on June 23, when Hansen was arrested for his first time, it was in West Virginia, the heart of coal country. Because coal is the largest single source of greenhouse gas emissions both in the United States and worldwide, and because there is enough coal left in the ground to heat the planet to catastrophic levels, that fossil fuel has been the focus of much new protest. As long as U.S. and European power plants continue spewing coal smoke, their governments will have absolutely no credibility in trying to influence the policies of rising economies such as China and India. Nonetheless, current U.S. legislation ensures that coal burning will continue largely unchecked for decades to come.

In West Virginia, concerns about coal’s impact on the atmosphere have intersected with a local environmental atrocity known as mountaintop-removal mining, a practice that Sens. John McCain and Barack Obama both claimed to oppose in the presidential campaign, but which continues today. This has made Appalachia the heart of direct action on the climate-change issue in the U.S. — or, as a blog tracking area protests puts it, “Climate Ground Zero.”

“You stand at the edge of one of these mountaintop removal sites and you’ll never feel the same way again,” says Mat Louis-Rosenberg, a staffer at Coal River Mountain Watch in southern West Virginia. The practice turns rolling mountains and valleys into flat, desolate moonscapes. Locals regularly hear the blasts of surface mines from their homes and then drink the resulting contaminants in their well water. When newly created lakes of toxic coal waste give way — as happened last December as a billion gallons of sludge flooded 300 acres of land near Harriman, Tenn. — they are the ones whose homes stand immediately downstream.

These dangers have given organizers a chance to create campaigns that connect the abstractions of climate change to specific sites of environmental ruin. “You can get a visceral and immediate sense of how bad this is,” says Louis-Rosenberg. “It’s not an invisible gas and a bunch of science that most people don’t understand.”

This year, in a series of escalating initiatives, environmentalists in the area have chained themselves to rock trucks, obstructed coal roads, and climbed up a huge crane-line mining machine to halt its work. A delegation of concerned citizens, including Hansen, crossed a police line onto the property of Massey Energy, a company responsible for mountaintop removals. Louis-Rosenberg places such direct action alongside a raft of other activities: community organizing, research for environmental impact statements, and gathering co-sponsors for a congressional ban on filling valleys with mining waste. “Ultimately, things will have to see their resolution in some sort of federal regulation or legislation,” he says. “But at this point there is not the political will to deal with the crisis. I see it as my role as an activist to create that political will.”

The next “Seattle moment”?

When the Kingsnorth decision was announced, an E.On representative said the company was “worried that this ruling will encourage other protestors to engage in similar actions at power plants across the country.” The worry was justified.

The diverse local protests taking place internationally are starting to feel like part of something larger, especially since they are already beginning to have an impact. Of the 214 new coal plants proposed in the United States since the year 2000, more than half have been canceled, abandoned, or put on hold. The Web site Coal Moratorium Now, which tracks public campaigns, shows that citizen dissent played a critical role in many of the cancellations or delays. Other results have been less obvious but no less real. Facing greater resistance, and the prospect of costly public relations battles, power companies are simply proposing to build fewer coal plants than was once the case.

Environmental organizers are planning for still larger mobilizations. In March, hundreds of people, including Hansen and 350.org campaign organizer Bill McKibben, joined in human chains to block the entrances to a target of enticing symbolic importance: Washington, D.C.’s Capitol Power Plant, a coal-burning facility built in 1910 that provides steam and refrigeration power to Capitol Hill. Police avoided making arrests, which could have easily exceeded highs for any previous act of civil disobedience around climate issues in American history. Nonetheless, the gathering produced a desired effect: House Speaker Nancy Pelosi and Senate Majority Leader Harry Reid sent a letter to Acting Architect of the Capitol Stephen Ayers requesting that the plant switch to natural gas.

On a global level, activists are starting to envision an international day of action that might launch disparate local campaigns into the mainstream spotlight and create a more unified global movement. A buzz of expectation and organizing now surrounds a December U.N. climate conference in Copenhagen, Denmark, where environmental ministers and other officials will gather to create a new treaty to replace the Kyoto protocol. The conference is taking place almost exactly 10 years after the 1999 Seattle protests, which overwhelmed the ministerial meetings of the World Trade Organization and altered the shape of globalization debates for years after.

Hopes for re-creating an event of that magnitude are based on more than just a coincidental anniversary year. Before Seattle, localized activity by global justice advocates had similarly swelled — with a wave of student anti-sweatshop drives, environmental boot camps, organic food gatherings, corporate ad spoofs, indigenous rights battles, and cross-border labor campaigns already simmering. Seattle united these into a recognized “movement of movements” more potent than the sum of its parts.

Organizers have suggested that as many as 100,000 people might take to the streets in Copenhagen. Among those planning around the Denmark conference, there is currently a debate about whether to converge on the conference itself or to target a heavily polluting company somewhere nearby as an example of bad climate-change behavior.

Likewise, in the United States, where events will be timed to take place in solidarity with the demonstrations in Copenhagen, there is a debate about whether to try to work with the Obama administration or turn up the heat on it. In the end, a range of tactics will no doubt be deployed in Copenhagen and in other cities around the world. A coalition of groups, including the normally satiric Yes Men, is managing a site called BeyondTalk.net, which allows people to sign a pledge expressing their willingness to join in nonviolent civil disobedience as the conference date nears.

As of this writing, 3,210 people have signed on. Compared with the numbers of people who will ultimately have to be persuaded of the need to act in order to force meaningful solutions to climate change, that remains a modest tally. In terms of the growing levels of dedication and personal sacrifice it represents, its significance is far greater. After all, that’s more than 3,000 people willing to take the chance that a determined action, even a botched one, might ultimately reverberate far and wide. It’s more than 3,000 people who may just be willing to climb for hours through a huge radiator in order to stop the planet from becoming one in all too short a time.