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Calvin Sims: Cosmochemistry depends on spectroscopy-the analysis of light by means of a spectrometer, which breaks up light, rainbow style, into its component colors. And those among us who feel that way then carry the nation, the world, into the future. I was three years old when John Glenn first orbited Earth. In there were two spacefarng nations.
These ambitions require not only money but also people smart enough to figure out how to tum them into reality, and visionary leaders to enable them. In China, with a population approaching 1.
Meanwhile, Europe and India are redoubling their efforts to conduct robotic science on spaceborne platforms, and there' s a growing interest in space exploration from more than a dozen other countries around the world, including Israel, Iran, Brazil, and Nigeria. China is building a new space launch site whose location, just nineteen degrees north of the equator, makes it geographically better for space launches than Cape Canaveral is for the United States.
This growing community of space-minded nations is hungry for its slice of the aerospace universe. In America, contrary to our self-image, we are no longer leaders, but simply players.
We've moved backward just by standing still. You can lear something deep about a nation when you look at what it accomplishes as a culture.
Do you know the most popular museum in the world over the past decade? It's not the Ufizi in Florence. It's not the Louvre in Paris. At a running average of some nine million visitors per year, it's the National Air and Space Museum in Washington, DC, which contains everything from the Wright Brothers' original aeroplane to the Apollo 11 Moon capsule, and much, much more.
Interational visitors are anxious to see the air and space artifacts housed in this museum, because they're an Amercan legacy to the world. More important, NASM represents the urge to dream and the will to enable it.
These traits are fundamental to being human, and have fortuitously coincided with what it has meant to be American. When you visit countries that don't nurture these kinds of ambitions, you can feel the absence of hope. Owing to all manner of politics, economics, and geography, people are reduced to worrying only about that day's shelter or the next day's meal. It's a shame, even a tragedy, how many people do not get to think about the future.
Technology coupled with wise leadership not only solves these problems but enables dreams of tomorrow. For generations, Americans have expected something new and better in their lives with every passing day-something that will make life a little more fun to live and a little more enlightening to behold. Exploration accomplishes this naturally. All we need to do is wake up to this fact. It's the Hubble Space Telescope, which has offered everybody on Earth a mind-expanding window to the cosmos.
But that hasn't always been the case. When it was launched in , a blunder in the design of the optics generated hopelessly blured images, much to everyone's dismay. Three years would pass before corrective optics were installed, enabling the sharp images that we now take for granted. What to do during the three years of fuzzy images?
It's a big, expensive telescope. Not wise to let it orbit idly. So we kept taking data, hoping some useful science would nonetheless come of it. Eager astrophysicists at Baltimore' s Space Telescope Science Institute, the research headquarters for the Hubble, didn't just sit around; they wrote suites of advanced image-processing software to help identify and isolate stars in the otherwise crowded, unfocused fields the telescope presented to them.
These novel techniques allowed some science to get done while the repair mission was being planned. Meanwhile, in collaboration with Hubble scientists, medical researchers at the Lombardi ComprehenSive Cancer Center at Georgetown University Medical Center in Washington, DC, recognized that the challenge faced by astrophysicists was similar to that faced by doctors in their visual search for tumors in mammograms.
With the help of funding from the National Science Foundation, the medical community adopted these new techniques to assist in the early detection of breast cancer. That means countless women are alive today because of ideas stimulated by a design faw in the Hubble Space Telescope. You cannot script these kinds of outcomes, yet they occur daily. The cross-pollination of disciplines almost always creates landscapes of innovation and discovery. And nothing accomplishes this like space exploration, which draws from the ranks of astrophysicists, biologists, chemists, engineers, and planetary geologists, whose collective efforts have the capacity to improve and enhance all that we have come to value as a modern society.
How many times have we heard the mantra "Why are we spending billions of dollars up there in space when we have pressing problems down here on Earth? Let's re-ask the question in an illuminating way: Half a penny.
I' d prefer it were more: Even during the storied Apollo era, peak NASA spending amounted to little more than four cents on the tax dollar. At that level, the Vision for Space Exploration would be sprinting ahead, funded at a level that could reclaim our preeminence on a frontier we pioneered. Instead the vision is just ambling along, with barely enough support to stay in the game and insuffcient support ever to lead it. So with more than ninety-nine out of a hundred cents going to fund all the rest of our nation' s priorities, the space program does not prevent nor has it ever prevented other things from happening.
Instead, America's former investments in aerospace have shaped our discovery-infused culture in ways that are obvious to the rest of the world. But we are a sufficiently wealthy nation to embrace this investment in our own tomorow-to drive our economy, our ambitions, and. You might see a vein of pink limestone on the wall of a canyon, a ladybug eating an aphid on the stem of a rose, a clamshell poking out of the sand. All you have to do is look. Board a jetliner crossing a continent, though, and those surface details soon disappear.
No aphid appetizers. No curious clams. Reach cruising altitude, around seven miles up, and identifying major roadways becomes a challenge. Detail continues to vanish as you ascend to space.
From the window of the International Space Station, which orbits at about miles up, you might find London, Los Angeles, New York, or Paris in the daytime, not because you can see them but because you leared where they are in geography class. At night their brilliant city lights present only the faintest glow. By day, contrary to common wisdom, with the unaided eye you probably won't see the pyramids at Giza, and you certainly won't see the Great Wall of China.
Their obscurity is partly the result of having been made from the soil and stone of the surrounding landscape. And although the Great Wall is thousands of miles long, it' s only about twenty feet wide-much narrower than the US interstate highways you can barely see from a transcontinental jet.
Plenty of natural scenery is visible, though: From the Moon, a quarter-million miles away, New York, Paris, and the rest of Earth' s urban glitter don't even show up as a twinkle. But from your lunar vantage you can still watch major weather fronts move across the planet.
Travel out to Neptune, 2. And what of Earth itself A speck no brighter than a dim star, all but lost in the glare of the Sun. And that's generous. Without the help of a picture caption, you might not find it at alL What would happen if some big-brained aliens from the great beyond scanned the skies with their naturally superb visual organs, further aided by alien state-of-the-art optical accessories?
What visible features of planet Earth might they detect? Blueness would be first and foremost. Water covers more than two-thirds of Earth' s surface; the Pacific Ocean alone makes up an entire side of the planet. Any beings with enough equipment and expertise to detect our planet' s color would surely infer the presence of water, the third most abundant molecule in the universe.
If the resolution of their equipment were high enough, the aliens would see more than just a pale blue dot. They would see intricate coastlines, too, strongly suggesting that the water is liquid. And smart aliens would surely know that if a planet has liquid water, the planet's temperature and atmospheric pressure fall within a well-determined range.
Earth's distinctive polar ice caps, which grow and shrink from the seasonal temperature variations, could also be seen optically. So could our planet's twenty-four-hour rotation, because recognizable landmasses rotate into view at predictable intervals. The aliens would also see major weather systems come and go; with careful study, they could readily distinguish features related to clouds in the atmosphere from features related to the surface of Earth itself.
We live within ten light-years of the nearest known exoplanet-that is, a planet orbiting a star other than the Sun. Most catalogued exoplanets lie more than a hundred light-years away. Earth's brightness is less than one-billionth that of the Sun, and our planet's proximity to the Sun would make it extremely hard for anybody to see Earth directly with an optical telescope. So if aliens have found us, they are likely searching in wavelengths other than visible light-or else their engineers are adapting some other strategy altogether.
Maybe they do what our own planet hunters typically do: A star's periodic jiggle betrays the existence of an orbiting planet that may otherwise be too dim to see directly.
The planet and host star both revolve around their common center of mass. The more massive the planet, the larger the star's orbit around the center of mass must be, and the more apparent the jiggle when you analyze the star's light. Unfortunately for planet-hunting aliens, Earth is puny, and so the Sun barely budges, posing a further challenge to alien engineers.
Radio waves might work, though. Maybe our eavesdropping aliens have something like the Arecibo Observatory in Puerto Rico, home of Earth's largest Single-dish radio telescope-which you might have seen in the early location shots of the movie LO1lOc , based on a novel by Carl Sagan.
Consider everything we've got that generates radio waves: Co if those alien eavesdroppers tum their own version of a radio telescope in our direction, they might infer that our planet hosts technology. One complication, though: Maybe they wouldn' t be able to distinguish Earth's signal from those of the larger planets in our solar system, all of which are sizable sources of radio waves.
Maybe they would think we're a new kind of odd, radio-intensive planet. Maybe they wouldn't be able to distinguish Earth's radio emissions from those of the Sun, forCing them to conclude that the Sun is a new kind of odd, radio-intensive star. Astrophysicists right here on Earth, at the University of Cambridge in England, were Similarly stumped back in While surveying the skies with a radio telescope for any source of strong radio waves, Anthony Hewish and his team discovered something extremely odd: Jocelyn Bell, a graduate student of Hewish's at the time, was the first to notice it.
Soon Bell' s colleagues established that the pulses came from a great distance. There' s also cosmochemistry. The chemical analysis of planetary atmospheres has become a lively feld of modem astrophysics. Cosmochemistry depends on spectroscopy-the analysis of light by means of a spectrometer, which breaks up light, rainbow style, into its component colors.
By exploiting the tools and tactics of spectroscopists, cosmochemists can infer the presence of life on an exoplanet, regardless of whether that life has sentience, intelligence, or technology. The method works because every element, every molecule-no matter where it exists in the universe-absorbs, emits, refects, and scatters light in a unique way. Pass that light through a spectrometer, and you'll fnd features that can rightly be called chemical fngerprints.
The most visible fingerprints are made by the chemicals most excited by the pressure and temperature of their environment. Planetary atmospheres are crammed with such features. And if a planet is teeming with flora and fauna, its atmosphere will be crammed with biomarkers-spectral evidence of life.
Whether biogenic produced by any or all life-forms , anthropogenic produced by the widespread species Homo S'piens.
Unless they happen to be born with built-in spectroscopic sensors, space-snooping aliens would need to build a spectrometer to read our fingerprints. But above all, Earth would have to eclipse its host star or some other light source , permitting light to pass through our atmosphere and continue on to the aliens. That way, the chemicals in Earth's atmosphere could interact with the light, leaving their marks for all to see. Some molecules-ammonia, carbon dioxide, water-show up everywhere in the universe, whether life is present or not.
But others pop up especially in the presence of life itself. Among the biomarkers in Earth's atmosphere are ozone-destroying chlorofluorocarbons from aerosol sprays, vapor from mineral solvents, escaped coolants from refrigerators and air conditioners, and smog from the burning of fossil fuels. No other way to read that list: Another readily detected biomarker is Earth's substantial and sustained level of the molecule methane, more than half of which is produced by human-related activities such as fuel-oil production, rice cultivation, sewage, and the burps of domesticated livestock.
Most telling, however, would be all our free-floating oxygen, which constitutes a full fifth of our atmosphere. Lxygen-the third most abundant element in the cosmos, after hydrogen and helium-is chemically active, bonding readily with atoms of hydrogen, carbon, nitrogen, silicon, sulfur, iron, and so on.
Thus, for oxygen to exist in a steady state, something must be liberating it as fast as it's being consumed. Here on Earth, the liberation is traceable to life, Photosynthesis, carried out by plants and select bacteria, creates free oxygen in the oceans and in the atmosphere. Free oxygen, in turn, enables the existence of oxygen-metabolizing creatures, including us and practically every other creature in the animal kingdom. We earthlings already know the Signifcance of Earth's distinctive chemical fngerprints.
But distant aliens who come upon us will have to interpret their findings and test their assumptions. Must the periodic appearance of sodium be technogenic? Free oxygen is surely biogenic. How about methane? It, too, is chemically unstable, and yes, some of it is anthropogenic. The rest comes from bacteria, cows, permafrost, soils, termites, wetlands, and other living and nonliving agents.
In fact, at this very moment, astrobiologists are arguing about the exact origin of trace amounts of methane on Mars and the copious quantities of methane detected on Saturn' s moon Titan, where we presume cows and termites surely do not dwell.
If the aliens decide that Earth's chemical features are strong evidence for life, maybe they'll wonder if the life is intelligent. Presumably the aliens communicate with one another, and perhaps they'll presume that other intelligent life-forms communicate too.
Maybe that's when they'll decide to eavesdrop on Earth with their radio telescopes to see what part of the electromagnetic spectrum its inhabitants have mastered. So, whether the aliens explore with chemistry or with radio waves, they might come to the same conclusion: Lur catalogue of exoplanets is growing apace. After all, the known universe harbors a hundred billion galaxies, each with hundreds of billions of stars. The search for life drives the search for exoplanets, some of which prouablj luuk like EarLh-nul in deLail, of course, bUl in overall properties.
Those are the planets our descendants might want to visit someday, by choice or by necessity. So far, though, nearly all the exoplanets detected by the planet hunters are much larger than Earth. Most are at least as massive as Jupiter, which is more than three hundred times Earth's mass. Nevertheless, as astrophYSiCists design hardware that can detect smaller and smaller jiggles of a host star, the ability to find punier and punier planets will grow. In spite of our impressive tally, planet hunting by earthlings is still in its horse-and-buggy stage, and only the most basic questions can be answered: Is the thing a planet?
How massive is it? How long does it take to orbit its host star? No one knows for sure what all those exoplanets are made of, and only a few of them eclipse their host stars, permitting cosmochemists to peek at their atmospheres.
But abstract measurements of chemical properties do not feed the imagination of either poets or scientists. We have to do better than the pale blue dot. Only then will we be able to conjure what a faraway planet looks like when seen from the edge of its own star system-or perhaps from the planet's surface itself. For that, we will need spaceborne telescopes with stupendous light-gathering power.
We're not there yet. But perhaps the aliens are. Attention was generated not so much by the discovery of exoplanets but by the prospect of their hosting intelligent life. In any case, the media frenzy that followed was somewhat out of proportion to the events. Because planets cannot be all that rare in the universe if the Sun happens to have eight of them. Also, the frst round of newly discovered planets were all oversize gas giants that resemble Jupiter, which means they have no convenient surface upon which life as we know it could exist.
At the moment, life on Earth is the only known life in the universe. The reasoning is easy: To declare that Earth must be the only planet in the universe with life would be inexcusably big-headed of us.
Many generations of thinkers, both religious and scientific, have been led astray by anthropocentric assumptions and simple ignorance. In the absence of dogma and data, it is safer to be gUided by the notion that we are not special, which is generally known as the Coperican principle. It was the Polish astronomer Nicolaus Copernicus who, in the mid-lS00s, put the Sun back in the middle of our solar system where it belongs. In spite of a third-century M. In the West, it was codified by the teachings of Aristotle and Ptolemy and later by the preachings of the Roman Catholic Church.
The Copernican principle comes with no guarantees that it will gUide us correctly for all scientific discoveries yet to come.
But it has revealed itself in our humble realization that Earth is not in the center of the solar system, the solar system is not in the center of the Milky Way galaxy, and the Milky Way galaxy is not in the center of the universe.
And in case you are one of those people who think that the edge may be a special place, we are not at the edge of anything either. A wise contemporary posture would be to assume that life on Earth is not immune to the Copernican principle. How, then, can the appearance or the chemistry of life on Earth provide clues to what life might be like elsewhere in the universe'!
I do not know whether biologists walk around every day awestruck by the diversity of life. I certainly do. On our planet, there coexist among countless other life-forms algae, beetles, sponges, jellyfish, snakes, condors, and giant sequoias. If you didn't know better, you would be hard pressed to believe that they all came from the same universe, much less the same planet. And by the way, try describing a snake to somebody who has never seen one: There' s this animal on Earth that 1 can stalk its prey with infrared detectors, 2 can swallow whole, live animals several times bigger than its head, 3 has no arms or legs or any other appendage, and yet 4 can travel along the ground at a speed of two feet per second!
Given the diversity of life on Earth, one might expect diversity among Hollywood aliens. But I am consistently amazed by the film industry's lack of creativity. A Space Odyssey -Hollywood's aliens look remarkably humanoid. No matter how ugly or cute they are, nearly all of them have two eyes, a nose, a mouth, two ears, a neck, shoulders, arms, hands, fingers, a torso, two legs, two feet-and they can walk.
Anatomically, these creatures are practically indistinguishable from humans, yet they are supposed to have come from another planet. If anything is certain, it is that life elsewhere in the universe, intelligent or otherwise, will look at least as exotic to us as some of Earth's own life-forms do. Is LA an alien space port? Jan Like the big LAX letters at airport. Visible from space? Must be where aliens land Jan The elements hydrogen, oxygen, and carbon account for more than 95 percent of the atoms in the human body and in all other known life.
Curiously, the study of life elsewhere in the universe is known as exobiology, one of the few disciplines that attempt to function, at least for now, in the complete absence of firsthand data. Is life chemically special? The Copernican principle suggests that it probably isn't. Aliens need not look like us to resemble us in more fundamental ways.
Consider that the four most common elements in the universe are hydrogen, helium, carbon, and oxygen. Helium is inert. So the three most abundant, chemically active ingredients in the cosmos are also the top three ingredients of life on Earth.
For this reason, you can bet that if life is found on another planet. Conversely, if life on Earth were composed primarily of manganese and molybdenum, then we would have excellent reason to suspect we're something special in the universe. Appealing once again to the Copernican principle, we can assume that an alien organism is not likely to be ridiculously large compared with life as we know it.
There are cogent structural reasons why you would not expect to fnd a life-form the size of the Empire State Building strutting around a planet. Even if we ignore the engineering limitations of biological matter, we approach another, more fundamental limit. If we assume that an alien has control of its own appendages, or more generally, if we assume the organism functions coherently as a system, then its size would ultimately be constrained by its ability to send signals within itself at the speed of light-the fastest allowable speed in the universe.
For an admittedly extreme example, if an organism were as big as the orbit of Neptune about ten light-hours across , and if it wanted to scratch its head, then this simple act would take no less than ten hours to accomplish.
Subslothlike behavior such as this would be evolutionarily self-limiting, because the time since the beginning of the universe might well be insufficient for the creature to have evolved from smaller forms. How about intelligence? When Hollywood aliens manage to visit Earth, one might expect them to be remarkably smart. But I know of some that should have been embarrassed by their stupidity. Surfing the FM dial during a car trp from Boston to New York City some years ago, I came upon a radio play in progress that, as best as I could determine, was about evil aliens that were terrorizing earthlings.
Apparently, they needed hydrogen atoms to survive, so they kept swooping down to Earth to suck up its oceans and extract the hydrogen from all the H20 molecules. Now those were some dumb aliens. They must not have been looking at other planets en route to Earth, because Jupiter, for example, contains more than two hundred times the entire mass of Earth in pure hydrogen. I guess nobody told them that more than 90 percent of all atoms in the universe are hydrogen.
And what about aliens that manage to traverse thousands of light-years through interstellar space yet bungle their arival by crash-landing on Earth? Then there are the aliens in the film Close Encounters of the Third Kind, who, in advance of their arival, beam to Earth a mysterious sequence of numbers that is eventually decoded by earthlings to be the latitude and longitude of their upcoming landing site. But Earth's longitude has a completely arbitrary starting pOint-the prime meridian-which passes through Greenwich, England, by international agreement.
And both longitude and latitude are measured in unnatural units we call degrees, of which are in a circle. It seems to me that, armed with this much knowledge of human culture, the aliens could have just leared English and beamed the message "We're going to land a little bit to the side of Devil ' s Tower National Monument in Wyoming.
And because we're ariving in a flying saucer, we won't need runway lights. Do they have problems with stairs? Or are fying saucers just handicap-accessible? The Motion Pictlre. An ancient mechanical space probe, V' ger had been rescued by a civilization of mechanical aliens and reconfigured so that it could accomplish its mission of discovery across the entire cosmos. The thing grew and grew, acquiring all knowledge of the universe and eventually achieving consciousness. Clued in by the badly tarnished letters "oya" on the original probe, Captain Kirk realizes that V'ger is actually Voyager 6, launched by earthlings in the late twentieth century.
What irks me is how V' ger acquired total knowledge of the cosmos yet remained clueless that its real name was Voyager. And don't get me started on the blockbuster Independence Day. Actually, I find nothing particularly offensive about evil aliens. There would be no science-fiction film industry without them. The aliens in Independence Dayare definitely evil. They look like a genetic cross between a Portuguese man-of-war, a hammerhead shark, and a human being.
But while they're more creaLively conceived lhan musl Hullywuud aliens, why are lheir fying saucers equipped with upholstered high-back chairs with armrests? I' m glad that, in the end, the humans win. We conquer the Independence Day aliens by having a Macintosh laptop computer upload a software virus to the mothership which happens to be one-fifth the mass of the Moon , thus disarming its protective force field. There is only one solution: Let us assume, for the sake of argument, that humans are the only species on Earth to have evolved high-level intelligence.
I mean no disrespect to other big-brained mammals. While most of them cannot do astrophysics, my conclusions are not substantially altered if you wish to include them. If life on Earth offers any measure of life elsewhere in the universe, then intelligence must be rare. By some estimates, there have been more than ten billion species in the hiStory of life on Earth. It follows that, among all extraterrestrial life-forms, we might expect no better than about one in ten billion to be as intelligent as we are-not to mention the odds against the intelligent life having an advanced technology and a desire to communicate through the vast distances of interstellar space.
But we humans have had command of the electromagnetic spectrum for less than a century, To put that more depressingly: For all we know, the aliens may have tried to get in touch centuries ago and have concluded that there is no intelligent life on Earth. They would now be looking elsewhere. A more humbling possibility is that aliens did become aware of the technologically profcient species that now inhabits Earth, and drew the same conclusion. Our Copernican perspective regarding life on Earth, intelligent or otherwise, requires us to presume that liquid water is a prerequisite to life elsewhere.
To support life, a planet cannot orbit its host star too closely, or else the temperature would be too high and the planet' s water content would vaporize. Also, the orbit should not be too far away, or else the temperature would be too low and the planet' s water content would freeze.
Any visible sunlight that manages to pass through its thick atmosphere of carbon dioxide gets absorbed by Venus' s surface and then reradiated in the infrared part of the spectrum. The infrared, in turn, gets trapped by the atmosphere.
At that temperature, lead would sWifty become molten. The discovery of simple, unintelligent life-forms elsewhere in the universe or evidence that they once existed would be far more likely-and, for me, only slightly less exciting-than the discovery of intelligent life. Two excellent nearby places to look are beneath the dried riverbeds of Mars where there may be fossil evidence of life that thrved when waters formerly flowed and the subsurface oceans that are theorized to exist under the frozen ice layers of Jupiter' s moon Europa, whose interior is kept warm by gravitational stresses from the Jovian system.
Once again, the promise of liquid water leads our search. Other common prerequisites for the evolution of life in the universe involve a planet in a stable, nearly circular orbit around a single star. With binary and multiple star systems, which make up more than half of all stars in the galaxy, orbits tend to be strongly elongated and chaotic, which induces extreme temperature swings that would undermine the evolution of stable life-forms.
We also require suficient time for evolution to run its course. High-mass stars are so short-lived a few million years that life on Earthlike planets in orbit around them would never have a chance to evolve. The Drake equation is more accurately viewed as a fertile idea rather than a rgorous statement of how the physical universe works. It separates the overall probability of finding life in the galaxy into a set of Simpler probabilities that correspond to our preconceived notions of suitable cosmic conditions.
In the end, after you argue with your colleagues about the value of each probability term in the equation, you are lef with an estimate for the total number of intelligent, technologically profiCient civilizations in the galaxy.
Depending on your bias level-and your knowledge of biology, chemistry, celestial mechanics, and astrophysics-your estimate may range from at least one ours up to millions of civilizations in the Milky Way alone. Presumably, an advanced civilization would have easy access to an abundant source of energy. These are the civilizations that would be more likely to do the sending. The search for extraterrestrial intelligence affectionately known by its acronym, SETI has taken many forms.
Long- established efforts have relied on monitoring billions of radio channels in search of a radio or microwave signal that might rise above the cosmic noise. More recently, improvements in laser technology have made it worthwhile to search the optical part of the electromagnetic spectrum for pulses of laser light a few nanoseconds in duration. During those nanoseconds, an intense, directed beam of visible light can outshine the light of nearby stars, allowing it to be detected from afar.
Another new approach, inspired by the optical version of SETI, is to keep a lookout across the galaxy, not for sustained signals, but for brief blasts of microwaves, which would be relatively cost-effcient to produce on the other end. The discovery of extraterestrial intelligence, if and when it happens, will impart a change in human self-perception that may be impossible to anticipate.
My only hope is that every other civilization isn't doing exactly what we are doing-because then everybody would be listening, nobody would be sending, and we would collectively conclude there is no other intelligent life in the universe.
Even if we don't soon fnd life, we will surely keep looking, because we are intellectual nomads-curious beings who derive almost as much fulfillment from the search as we do from the discovery.
Here' s a question: Do you believe in UFOs? If so, you're in some pretty impressive company.
British astrophysicist Stephen Hawking, arguably one of the smartest people on the planet, thinks there's a good chance that alien life exists-and not exactly the friendly ET kind. In fact, Hawking envisions a far darker possibility, more along the lines of the movie War of the Worlds. In a documentary for the Discovery Channel, Hawking says the aliens will be big, bad, and very busy conquering planet after planet.
He says they might live in massive ships, and he calls them nomads who travel the universe conquering others and collecting energy through mirrors. Mirrors; massive ships; giant, mean aliens: I've been fascinated by this since I was a kid, given the fact that there are hundreds of billions of galaxies, with hundreds of millions of stars in each galaxy.
Nei deGrse Tyon: Hundreds of billions in each galaxy. Hundreds of billions of stars-even more. And that probably means there's life out there somewhere. NDT' Indeed. But this idea that aliens will be evil-Hawking paints a picture that is far less ET and far more Independence Day-is this speculation?
NDT Yes, but it's not blind speculation. It says more about what we fear about ourselves than any real expectations of what an alien would be like. In other words, I think our biggest fear is that the aliens who visit us would treat us the way we treat each other here on Earth. So, in a way, Hawking' s apocalyptic fear stories are a mirror held back up to us.
That's a very different perspective than what Carl Sagan put out there. He was literally giving away Earth' s location. NDT Exactly. Sagan provided the return address on a plaque on the Voyager spacecraft. SO why would aliens do what Hawking proposes they'll do?
Some sort of vengeance? NDT Like I said, no one knows how aliens will behave. They will have different chemistry, different motives, different intentions. How can we extrapolate from ourselves to them? Any suspicion that they will be evil is more a reflection of our fear about how we would treat an alien species if we found them than any actual knowledge about how an alien species would treat as.
How ""hi' ld sneezes in space, you ask? Helmet blocks all We're listening for them right now. My understanding is that we've been listening for a long time-for anything-and we haven' t heard a peep from out there. Do you think they're listening to us right now?
NDT Possibly. The big fear, it seems to me, is that we announce our presence and then the aliens come and enslave us or put us in a zoo.
Some entertaining science-fiction stories have captured just those themes. I never thought to imagine us as living in an alien zoo. NDT That' s the fear factor. But what are we doing? We're mostly listening. We have giant radio telescopes pointing in different directions, with highly sophisticated circuitry that listens to billions of radio frequencies simultaneously to see if anybody is whispering on any one of them anyplace in the universe.
That's different from sending signals out. We're not sending signals out on purpose; we're sending them out accidentally. The expanding edge of our radio bubble is about seventy light-years away right now, and on that frontier you'll find broadcast television shows like I Love Lacy and The Honeymoonersthe first emissaries of human culture that the aliens would decode. Not much reason there for aliens to fear us, but plenty of reason for them to question our intelligence.
And, rumors to the contrary, we have not yet heard from aliens, even accidentally. So we're confronting a vacuum, ready to be filled with the many fears we harbor. So how can this comparative statistic be true? The impact record shows that by the end of ten million years, when the sum of all airplane crashes has killed a billion people assuming a death-by-airplane rate of a hundred per year , an asteroid large enough to kill the same number of people will have hit Earth. The difference is that while airplanes are continually killing people a few at a time, [hat asteroid might not kill anybody for millions of years.
But when it does hit, it will take out a billion people: The combined impact rate for asteroids and comets in the early solar system was frighteningly high.
Theories of planet formation show that chemically rich gas cooled and condensed to form molecules, then particles of dust, then rocks and ice. Thereafter, it was a shooting gallery. Collisions served as a means for chemical and gravitational forces to bind smaller objects into larger ones. Those objects that, by chance, had accreted slightly more mass than average had slightly higher gravity, attracting other objects even more.
As accretion continued, gravity eventually shaped blobs into spheres, and planets were born. The most massive planets had sufcient gravity to retain the gaseous envelope we call an atmosphere. Every planet continues to accrete, every day of its life, although at a significantly lower rate than when it first formed.
The rest harmlessly vapozes in Earth's atmosphere as shooting stars. More hazardous are the billions, likely trillions, of leftover rocks-comets and asteroids-that have been orbiting the Sun since the early years of our solar system but haven' t yet managed to join up with a larger object. Long-period comets-icy vagabonds from the extreme reaches of the solar system as much as a thousand times the radius of Neptune' s orbit -are susceptible to gravitational nudges from passing stars and interstellar clouds, which can direct them on a long journey inward toward the Sun, and therefore to our neighborhood.
Several dozen short-period comets from the nearer reaches of the solar system are known to cross Earth's orbit. As for the asteroids, most are made of rock. The rest are metal, mostly iron. Some are rubble piles-gravitationally bound collections of bits and pieces. Most asteroids live between the orbits of Mars and Jupiter and will never ever come near Earth.
But some do. Some will. About ten thousand near-Earth asteroids are known, with more surely to be discovered. The most threatening of them number more than a thousand, and that number steadily grows as spacewatchers continually survey the skies in search of them. Nobody's saying they're all going to hit tomorrow. But all of them are worth watching, because a little cosmic nudge here or there might just send them a little closer to us.
In this game of gravity, by far the scariest impactors are the long-period comets-those whose orbits around the Sun take longer than two hundred years. Representing about one-fourth of Earth's total risk of impacts, such comets fall toward the inner solar system from gargantuan distances and achieve speeds in excess of a hundred thousand miles an hour by the time they reach Earth. Long-period comets thus achieve more awesome impact energy for their size than your run-of-the-mill asteroid.
More important, they are too distant, and too dim, throughout most of their orbit to be reliably tracked. By the time a long-period comet is discovered to be heading our way. While en route, it came within ten million miles of Earth: Impacts made us what we are today, So, we cannot Simultaneously be happy that we live on a planet.
Sonic booms are shock waves too, but they're typically made by airplanes with speeds between one and three times the speed of sound. The worst damage they might do is jiggle the dishes in your china cabinet. But at speeds in excess of 45, miles per hour-nearly seventy times the speed of sound -the shock waves from the average collision between an asteroid and Earth can be devastating.
If the asteroid or comet is large enough to survive its own shock waves, the rest of its energy gets deposited on Earth.
The impact blows a crater up to twenty times the diameter of the original object and melts the ground below. If many impactors hit one after another, with little time between each strike, then Earth' s surface will not have enough time to cool between impacts.
We infer from the pristine cratering record on the surface of our nearest neighbor, the Moon, that Earth experienced such an era of heavy bombardment between 4. The oldest fossil evidence for life on Earth dates from about 3. Before that, Earth's surface was being relentlessly sterilized. The formation of complex molecules, and thus life, was inhibited, although all the basic ingredients were being delivered.
That would mean it took million years for life to emerge here 4. But to be fair to organic chemistry, you must first subtract all the time that Earth' s surface was forbiddingly hot. Puch of that water was delivered to Earth by comets more than four billion years ago. But not all space debris is lef over from the beginning of the solar system. Earth has been hit at least a dozen times by rocks ejected from Mars, and we've been hit countless more times by rocks ejected from the Moon.
Ejections occur when impactors car so much energy that, when they hit, smaller rocks near the impact zone are thrust upward with sufficient speed to escape a planet' s gravitational grip. Aferward, those rocks mind their own ballistic business in orbit around the Sun until they slam into something.
The most famous of the Mars rocks is the first meteorite found near the Alan Hills section of Antarctica in ofcially known by its coded though sensible abbreviation, ALH This meteorite contains tantalizing, yet circumstantial, evidence that simple life on the Red Planet thrived a billion years ago.
Since liquid water is crucial to the survival of life as we know it, the possibility of life on Mars does not stretch scientific credulity. The fun part comes with the speculation that life-forms frst arose on Mars and were blasted off the planet's surface, thus becoming the solar system's first microbial astronauts, ariving on Earth tojump-start evolution. There's even a word for that process: Maybe we are all Martians. Matter is far more likely to travel from Mars to Earth than vice versa.
Escaping Earth's gravity requires more than two and a half times the energy required to leave Mars. And since Earth's atmosphere is about a hundred times denser, air resistance on Earth relative to Mars is formidable.
Bacteria on a voyaging asteroid would have to be hardy indeed to survive several million years of interplanetary wanderings before plunging to Earth. Fortunately, there is no shortage of liquid water and rich chemistry here at home, so even though we still cannot defnitively explain the origin of life, we do not require theores of panspermia to do so. Lf course, it's easy to think impacts are bad for life. We can and do blame them for major episodes of extinction in the fossil record.
That record displays no end of extinct life-forms that thrived far longer than the current Earth tenure of Homo sapiens. Dinosaurs are among them. But what are the ongoing rsks to life and society? House-size impactors collide with Earth, on average, every few decades. Typically they explode in the atmosphere, leaving no trace of a crater. But even baby impacts could become political time bombs. If such an atmospheric explosion occurred over India or Pakistan during one of the many episodes of escalated tension between those two nations, the rsk is high that someone would misinterpret the event as a first nuclear strike, and respond accordingly.
At the other end of the impactor scale, once in about a hundred million years we're visited by an impactor capable of annihilating all life-forms bigger than a carry-on suitcase. In cases such as those, no political response would be necessary. It's based on a detailed analysis of the history of impact craters on Earth, the erosion-free cratering record on the Moon's surface, and the known numbers of asteroids and comets whose orbits cross that of Earth.
These data are adapted from a congressionally mandated study titled The Spaceguard Survey: For comparison, the table includes the impact energ in units of the atomic bomb dropped by the US Air Force on Hiroshima in The culprit is believed to have been a sixty-meter stony meteorite about the size of a twenty-story building that exploded in midair, thus leaving no crater.
The chart indicates that collisions of this magnitude happen, on average, every couple of centuries. This is one of those collisions that take place once in a hundred million years. The crater dates from about sixty-five million years ago, and there hasn' t been one of similar magnitude since. It' s useful to consider how strikes by comets and asteroids impact Earth's ecosystem. In a fat book titled Hazards Due to Comets and Asteroids. Here' s a bit of what they sketched out: The few that survive in one piece are likely to be iron based.
On land, the iron impactor will destroy an area equivalent to Washington, DC. An oceanic impact of that magnitude will produce significant tidal waves. An oceanic impact will generate tidal waves on an entire hemisphere, while a land impact will raise enough dust into the stratosphere to alter Earth's weather and freeze crops.
A land impact will destroy an area the size of France. A land impact will destroy an area equivalent to the continental United States. Earth, of course, is not the only rocky planet at risk of impacts.
Mercury has a cratered face that, to a casual observer, looks just like the Moon. Radio topography of cloud-enshrouded Venus shows no shortage of craters. And Mars, with its historically active geology, reveals large, recently formed craters.
At more than three hundred times the mass of Earth, and more than ten times its diameter, Jupiter' s ability to attract impactors is unmatched among the planets of our solar system. Backyard telescopes down here on Earth easily detected the gaseous scars. Because Jupiter rotates SWiftly once every ten hours , each piece of the comet plunged into a different location as the atmosphere slid by.
In case you were wondering, each piece of Shoemaker-Levy 9 hit with the equivalent energy of the Chicxulub impact. So, whatever else is true about Jupiter, it surely has no dinosaurs left. True, our list of potential killer impactors is incomplete, and our ability to predict the behavior of objects millions of orbits into the future is severely compromised by the onset of chaos. But we can focus on what will happen in the next few decades or centuries.
Among the population of Earth-crossing asteroids, we have a chance at cataloguing everything larger than about one kilometer wide-the size that begins to wreak global catastrophe. Unfortunately, objects much smaller than a kilometer, of which there are many, reflect much less light and are therefore much harder to detect and track.
Because of their dimness, they can hit us without notice-or with notice far too short for us to do anything about them. In January , for instance, a stadium-size asteroid passed by at about twice the distance from here to the Moon-and it was discovered just twelve days before its closest approach.
Given another decade or so of data collecting and detector improvements, however, it may be possible to catalogue nearly all asteroids down to about meters across. While the small stuff carries enough energy to incinerate entire nations, it will not put the human species at risk of extinction. Any of these we should wor about? At least one.
On Friday the 13th, April , an asteroid large enough to fill the Rose Bowl as though it were an egg cup will fy so close to Earth that it will dip below the altitude of our communication satellites.
We did not name this asteroid Bambi. Instead, we named it Apophis, after the Egyptian god of darkness and death. If the trajectory of Apophis at close approach passes within a narrow range of altitudes called the "keyhole," then the infuence of Earth's gravity on its orbit will guarantee that seven years later, in , on its next trip around, the asteroid will hit Earth directly, likely slamming into the Pacific Ocean between California and Hawaii.
The five-story tsunami it creates will wipe out the entire west coast of North America, dunk Hawaiian cities, and devastate all the landmasses of the Pacific Rim. If Apophis misses the keyhole in , we will have nothing to worry about in Once we mark our calendars for , we can either pass the time sipping cocktails at the beach and planning to hide from the impact, or we can be proactive.
The battle C of those anxious to wage nuclear war is "Blow it out of the sky! A direct hit on an incoming asteroid might explode it into enough small pieces to reduce the impact danger to a harmless, though spectacular, meteor shower.
Note that in empty space, where there is no air, there can be no shock waves, and so a nuclear warhead must actually make contact with the asteroid to do damage. Another method would be to engage a radiation-intensive neutron bomb that' s the Cold War-era bomb that kills people but leaves buildings intact. The bomb's high-energy neutron bath would heat up one side of the asteroid, causing material to spew forth and thus induce the asteroid to recoil.
That recoil would alter the asteroid's orbit and remove it from the collision path. A kindler, gentler method would be to nudge the asteroid out of harm' s way with slow but steady rockets that have somehow been attached to one side. Apart from the uncertainty of how to attach rockets to an unfamiliar material, if you do this early enough, then all you need is a small push using conventional chemical fuels.
Or maybe you attach a solar sail, which harnesses the pressure of sunlight for its propulsion, in which case you'll need no fuel at all.
The odds-on favorite solution, however, is the gravitational tractor. This involves parking a probe in space near the killer asteroid. As their mutual gravity draws the probe to the asteroid, an aray of retro rockets fres, instead causing the asteroid to draw toward the probe and off its collision course with Earth. The business of saving the planet requires commitment. We must first catalogue every object whose orbit intersects Earth's.
We must then perform precise computer calculations that enable us to predict a catastrophic collision hundreds or thousands of orbits into the future. Meanwhile, we must also carry out space missions to determine in great detail the structure and chemical composition of killer comets and asteroids.
Military strategists understand the need to know your enemy. But now, for the frst time, we would be engaged in a space mission conceived not to beat a spacefarng competitor but to protect the life of our entire species on our collective planetary home.
Whichever option we choose, we will first need that detailed inventory of orbits for all objects that pose a rsk to life on Earth. The number of people in the world engaged in that search totals a few dozen. I' d feel more comfortable if there were a few more. The decision comes down to how long into the future we're willing to protect the life of our own species on Earth.
If humans one day become extinct from a catastrophic collision, it won't be because we lacked the brainpower to protect ourselves, but because we lacked the foresight and determination.
The dominant species that replaces us on postapocalyptic Earth might just wonder why we fared no better than the proverbially pea-brained dinosaurs. We need to go back to the Moon.
Many people say, "We've been there, done that, can't you come up with a new place to visit? A trip to Mars takes about nine months.
If you haven' t been out of low Earth orbit for forty years, sending people to Mars for the frst time is a long way to go and a hard thing to do. A big thrust of the new space vision is to reengage the manned program in ways that haven't been done during the past decade, and to recapture the excitement that drove so much of the space program back in the s.
Calvin Sims: So the reasons to go are to prove that we can do it again, because we haven' t done H in such a long time, and also to build consensus for it? NDT We haven' t left low Earth orbit recently. We have to remind ourselves how to do that-how to do it well, how to do it efficiently. We also have to figure out how to set up base camp and sustain life in a place other than Earth or low Earth orbit.
The Moon is a relatively easy place to get to and test all this out. Do you think it's prudent to be funding this effort, especially at a point in our history when we have a war in Iraq and a lot of domestic demands? It doesn't come all at once; it's spread over multiple years.
America is a wealthy nation. Let's ask the question, "What is going to space worth to you? So I don't think that's the frst place people should be looking if they want to save money in the federal budget.
It' s certainly worth a whole percent-personally, I think it's worth more than that-but if all you're going to give us is one percent, we can make good use of it. Destied ror the Stars NDT In every culture across time, there has always been somebody wondering about our place in the universe and trying to come to terms with what Earth is.
This is not a latter-day interest; it's something deeply inherent in what it is to be human. As twenty-first-century Americans, we're lucky to be able to act on that wonder. Most people just stood there, looked upward, and invented mythologies to explain what they were wondering about. We actually get to build spaceships and go places. That' s a privilege brought by the success of our economy and the vision of our leaders, combined with the urge to do it in the first place.
You're saying the primary reason to venture into space is the quest for knowledge, and that humans are programmed by nature to satisfy our curiosity and to engage in the sheer thrill of discovery.
Why is the allure so great that we risk human lives to get there? NDT Not everyone would risk their life. But for some members of our species, discovery is fundamental to their character and identity. And those among us who feel that way then carry the nation, the world, into the future. Robots are important also. If I don my pure-scientist hat, I would say just send robots; I'll stay down here and get the data.
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