pale blue dot -carl sagan-第42章
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t misses or hits the Earth is entirely in our hands。 If we leave it alone； it misses。 If we push it cleverly and precisely； it hits。 Maybe we should call it 〃Eight Ball。〃
Now imagine a time； a few decades hence； when all such near…Earth asteroids are inventoried and their orbits piled。 Then； as Alan Harris of JPL； Greg Canavan of the Los Alamos National Laboratory； Ostro； and I have shown； it might take only a year to select a suitable object； alter its orbit； and send it crashing into the Earth with cataclysmic effect。
The technology required—large optical telescopes； sensitive detectors； rocket propulsion systems able to lift a few tons of payload and make precise rendezvous in nearby space； and thermonuclear weapons—all exist today。 Improvements in all but perhaps the last can be confidently expected。 If we're not careful； many nations may have these capabilities in the next few decades。 What kind of world will we then have made？
We have a tendency to minimize the dangers of new technologies。 A year before the Chernobyl disaster； a Soviet nuclear power industry deputy minister was asked about the safety of Soviet reactors； and chose Chernobyl as a particularly safe site。 The average waiting time to disaster； he confidently estimated； was a hundred thousand years。 Less than a year later 。 。 。 devastation。 Similar reassurances were provided by NASA contractors the year before the Challenger disaster： You would have to wait ten thousand years； they estimated； for a catastrophic failure of the shuttle。 One year later 。 。 。 heartbreak。
Chlorofluorocarbons （CFCs） were developed specifically as a pletely safe refrigerant—to replace ammonia and other refrigerants that； on leaking out； had caused illness and some deaths。 Chemically inert； nontoxic （in ordinary concentrations）； odorless； tasteless； non…allergenic； nonflammable； CFCs represent a brilliant technical solution to a well…defined practical problem。 They found uses in many other industries besides refrigeration and air conditioning。 But； as I described above； the chemists who developed CFCs overlooked one essential fact—that the molecules' very inertness guarantees that they are circulated to stratospheric altitudes and there cracked open by sunlight； releasing chlorine atoms which then attack the protective ozone layer。 Due to the work of a few scientists； the dangers may have been recognized and averted in time。 We humans have now almost stopped producing CFCs。 We won't actually know if we've avoided real harm for about a century； that's how long it takes for all the CFC damage to be pleted。 Like the ancient Camarinans； we make mistakes。* Not only do we often ignore the warnings of the Oracles； characteristically we do not even consult them。
* There is of course a wide range of other problems brought on by the devastatingly powerful technology we've recently invented。 But in most cases they're not Camarinan disasters…damned if you do and damned if you don't。 Instead they're dilemmas of wisdom or timing…for example； the wrong refrigerant or refrigeration physics out of many possible alternatives。
The notion of moving asteroids into Earth orbit has proved attractive to some space scientists and long…range planners。 They foresee mining the minerals and precious metals of these worlds or providing resources for the construction of space infrastructure without having to fight the Earth's gravity to get them up there。 Articles have been published on how to acplish this end and what the benefits will be。 In modern discussions； the asteroid is inserted into orbit around the Earth by first making it pass through and be braked by the Earth's atmosphere； a maneuver with very little margin for error。 For the near future we can； I think； recognize this whole endeavor as unusually dangerous and foolhardy； especially for metal worldlets larger than tens of meters across。 This is the one activity where errors in navigation or propulsion or mission design can have the most sweeping and catastrophic consequences。
The foregoing are examples of inadvertence。 But there's another kind of peril： We are sometimes told that this or that invention would of course not be misused。 No sane person would be so reckless。 This is the 〃only a madman〃 argument。 Whenever I hear it （and it's often trotted out in such debates）； I remind myself that madmen really exist。 Sometimes they achieve the highest levels of political power in modern industrial nations。 This is the century of Hitler and Stalin； tyrants who posed the gravest dangers not just to the rest of the human family； but to their own people as well。 In the winter and spring of 1945； Hitler ordered Germany to be destroyed—even 〃what the people need for elementary survival〃—because the surviving Germans had 〃betrayed〃 him； and at any rate were 〃inferior〃 to those who had already died。 If Hitler had had nuclear weapons； the threat of a counterstrike by Allied nuclear weapons； had there been any； is unlikely to have dissuaded him。 It might have encouraged him。
Can we humans be trusted with civilization…threatening technologies？ If the chance is almost one in a thousand that much of the human population will be killed by an impact in the next century； isn't it more likely that asteroid deflection technology will get into the wrong hands in another century—some misanthropic sociopath like a Hitler or a Stalin eager to kill everybody； a megalomaniac lusting after 〃greatness〃 and 〃glory；〃 a victim of ethnic violence bent on revenge； someone in the grip of unusually severe testosterone poisoning； some religious fanatic hastening the Day of judgment； or just technicians inpetent or insufficiently vigilant in handling the controls and safeguards？ Such people exist。 The risks seem far worse than the benefits； the cure worse than the disease。 The cloud of near…Earth asteroids through which the Earth plows may constitute a modern Camarine marsh。
It's easy to think that all of this must be very unlikely； mere anxious fantasy。 Surely sober heads would prevail。 Think of how many people would be involved in preparing and launching warheads； in space navigation； in detonating warheads； in checking what orbital perturbation each nuclear explosion has made； in herding the asteroid so it is on an impact trajectory with Earth； and so on。 Isn't it noteworthy that although Hitler gave orders for the retreating Nazi troops to burn Paris and to lay waste to Germany itself； his orders were not carried out？ Surely someone essential to the success of the deflection mission will recognize the danger。 Even assurances that the project is designed to destroy some vile enemy nation would probably be disbelieved； because the effects of collision are planet…wide （and anyway it's very hard to make sure your asteroid excavates its monster crater in a particularly deserving nation）。
But now imagine a totalitarian state； not overrun by enemy troops； but one thriving and self…confident。 Imagine a tradition in which orders are obeyed without question。 Imagine that those involved in the operation are supplied a cover story： The asteroid is about to impact the Earth； and it is their job to deflect it—but in order not to worry people needlessly； the operation must be performed in secret。 In a military setting with a mand hierarchy firmly in place； partmentalization of knowledge； general secrecy； and a cover story； can we be confident that even apocalyptic orders would be disobeyed？ Are we really sure that in the next decades and centuries and millennia； nothing like this might happen？ How sure are we？
It's no use saying that all technologies can be used for good or for ill。 That is certainly true； but when the 〃ill〃 achieves a sufficiently apocalyptic scale； we may have to set limits on which technologies may be developed。 （In a way we do this all the time； because we can't afford to develop all technologies。 Some are favored and some are not。） Or constraints may have to be levied by the munity of nations on madmen and autarchs and fanaticism。
Tracking asteroids and ets is prudent； it's good science； and it doesn't cost much。 But； knowing our weaknesses； why would we even consider now developing the technology to deflect small worlds？ For safety； shall we imagine this technology in the hands of many nations； each providing checks and balances against misuse by another？ This is nothing like the old nuclear balance of terror。 It hardly inhibits some madman intent on global catastrophe to know that if he does not hurry； a rival may beat him to it。 How confident can we be that the munity of nations will be able to detect a cleverly designed； clandestine asteroid deflection in time to do something about it？ If such a technology were developed； can any international safeguards be envisioned that have a reliability mensurate with the risk？
Even if we restrict ourselves merely to surveillance； there's a risk。 Imagine that in a generation we characterize the orbits of 30；000 objects of 100…meter diameter or more； and that this information is publicized； as of course it should be。 Maps will be published showing near…Earth space black with the orbits of asteroids and ets； 30；000 swords of Damocles hanging over our heads…ten times more than the number of stars visible to the naked eye under conditions of optimum atmospheric clarity。 Public anxiety might be much greater in such a time of knowledge than in our current age of ignorance。 There might be irresistible public pressure to develop means to mitigate even nonexistent threats； which would then feed the danger that deflection technology would be misused。 For this reason； asteroid discovery and surveillance may not be a mere neutral tool of future policy； but rather a kind of booby trap。 To me； the only foreseeable solution is a bination of accurate orbit estimation； realistic threat assessment； and effective public education—so that in democracies at least； the citizens can make their own； informed decisions。 This is a job for NASA。
Near…Earth asteroids； and means of altering their orbits； are being looked at seriously。 There is some sign that officials in the Department of Defense and the weapons laboratories are beginning to understand that there may be real dangers in planning to push asteroids around。 Civilian and military scientists have met to discuss the subject。 On first hearing about the asteroid hazard； many people think of it as a kind of Chicken Little fable； Goosey…Lucy； newly arrived and in great excitement； is municating the urgent news that the sky is falling。 The tendency to dismiss the prospect of any catastrophe that we have not personally witnessed is in the long run very foolish。 But in this case it may be an ally of prudence。
MEANWHILE WE MUST STILL FACE the deflection dilemma。 If we develop and deploy this technology； it may do us in。 If we don't； some asteroid or et may do us in。 The resolution of the dilemma hinges； I think； on the fact that the likely timescales of the two dangers are very different—short for the former； long for the latter。
I like to think that our future involvement with near…Earth asteroids will go something like this： From ground…based observatories； we discover all the big ones； plot and monitor their orbits； determine rotation rates and positions。 Scientists are
