pale blue dot -carl sagan-第46部分

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　numbers　of　inoffensive　asteroids　whose　orbits　could　be　altered　with　nuclear　warheads　so　they　quickly　collide　with　the　Earth。

Suppose　we　restrict　our　attention　to　the　2；000　or　so　near…Earth　asteroids　that　are　a　kilometer　across　or　bigger—that　is；　the　ones　most　likely　to　cause　a　global　catastrophe。　Today；　with　only　about　100　of　these　objects　catalogued；　it　would　take　about　a　century　to　catch　one　when　it's　easily　deflectable　to　Earth　and　alter　its　orbit。　We　think　we've　found　one；　an　as…yet…unnamed*　asteroid　so　far　denoted　only　as　1991OA。　In　2070；　this　world；　about　1　kilometer　in　diameter；　will　e　within　4。5　million　kilometers　of　the　Earth's　orbit—only　fifteen　times　the　distance　to　the　Moon。　To　deflect　1991OA　so　it　hits　the　Earth；　only　about　60　megatons　of　TNT　equivalent　needs　to　be　exploded　in　the　right　way—the　equivalent　of　a　small　number　of　currently　available　nuclear　warheads。

*　What　should　we　call　this　world？　Naming　it　after　the　Greek　Fates　or　Furies　or　Nemesis　seems　inappropriate；　because　whether　it　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