pale blue dot -carl sagan-第29章

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ense　oxygen　atmosphere　may　be　detectable　even　on　a　world　we've　never　imaged。　As　for　the　Earth；　that　may　by　itself　be　a　sign　of　life。　An　oxygen　atmosphere　with　appreciable　quantities　of　methane　would　almost　certainly　be　a　sign　of　life；　as　would　modulated　radio　emission。　Someday；　from　observations　of　our　planetary　system　or　another；　the　news　of　life　elsewhere　may　be　announced　over　the　morning　coffee。



THE　VOYAGER　SPACECRAFT　are　bound　for　the　stars。　They　are　on　escape　trajectories　from　the　Solar　System；　barreling　along　at　almost　a　million　miles　a　day。　The　gravitational　fields　of　Jupiter；　Saturn；　Uranus；　and　Neptune　have　flung　them　at　such　high　speeds　that　they　have　broken　the　bonds　that　once　tied　them　to　the　Sun。

Have　they　left　the　Solar　System　yet？　The　answer　depends　very　much　on　how　you　define　the　boundary　of　the　Sun's　realm。　If　it's　the　orbit　of　the　outermost　good…sized　planet；　then　the　Voyager　spacecraft　are　already　long　gone；　there　are　probably　no　undiscovered　Neptunes。　If　you　mean　the　outermost　planet；　it　may　be　that　there　are　other—perhaps　Triton…like—planets　far　beyond　Neptune　and　Pluto；　if　so；　Voyager　1　and　Voyager　2　are　still　within　the　Solar　System。　If　you　define　the　outer　limits　of　the　Solar　System　as　the　heliopause—where　the　interplanetary　particles　and　magnetic　fields　are　replaced　by　their　interstellar　counterparts—then　neither　Voyager　has　yet　left　the　Solar　System；　although　they　may　do　so　in　the　next　few　decades。*　But　if　your　definition　of　the　edge　of　the　Solar　System　is　the　distance　at　which　our　star　can　no　longer　hold　worlds　in　orbit　about　it；　then　the　Voyagers　will　not　leave　the　Solar　System　for　hundreds　of　centuries。

*　Radio　signals　that　both　Voyagers　detected　in　1992　are　thought　to　arise　from　the　collision　of　powerful　gusts　of　solar　wind　with　the　thin　gas　that　lies　between　the　stars。　From　the　immense　。power　of　the　signal　（over　10　trillion　watts）；　the　distance　to　the　heliopause　can　be　estimated：　about　100　times　the　Earth's　distance　from　the　Sun。　At　the　speed　it's　leaving　the　Solar　System；　Voyager　1　might　pierce　the　heliopause　and　enter　interstellar　space　around　the　year　2010。　If　its　radioactive　power　source　is　still　working；　news　of　the　crossing　will　be　radioed　back　to　the　stay…at…homes　on　Earth。　The　energy　released　by　the　collision　of　this　shock　wave　with　the　heliopause　makes　it　the　most　powerful　source　of　radio　emission　in　the　Solar　System。　It　makes　you　wonder　whether　even　stronger　shocks　in　other　planetary　systems　might　he　detectable　by　our　radio　telescope。

Weakly　grasped　by　the　Sun's　gravity；　in　every　direction　in　the　sky；　is　that　immense　horde　of　a　trillion　ets　or　more；　the　port　Cloud。　The　two　spacecraft　will　finish　their　passage　through

the　Oort　cloud　in　another　20；000　years　or　so。　Then；　at　last；　pleting　their　long　good…bye　to　the　Solar　System；　broken　free　of　the　gravitational　shackles　that　once　bound　them　to　the　Sun；　the　Voyagers　will　make　for　the　open　sea　of　interstellar　space。　only　then　will　Phase　Two　of　their　mission　begin。

Their　radio　transmitters　long　dead；　the　spacecraft　will　wander　for　ages　in　the　calm；　cold　interstellar　blackness—where　there　is　almost　nothing　to　erode　them。　Once　out　of　the　Solar　System；　they　will　remain　intact　for　a　billion　years　or　more；　as　they　circumnavigate　the　center　of　the　Milky　Way　galaxy。

We　do　not　know　whether　there　are　other　space…faring　civilizations　in　the　Milky　Way。　If　they　do　exist；　we　do　not　know　how　abundant　they　are；　much　less　where　they　are。　But　there　is　at　least　a　chance　that　sometime　in　the　remote　future　one　of　the　Voyagers　will　be　intercepted　and　examined　by　an　alien　craft。

Accordingly；　as　each　Voyager　left　Earth　for　the　planets　and　the　stars；　it　carried　with　it　a　golden　phonograph　record　encased　in　a　golden；　mirrored　jacket　containing；　among　other　things；　greetings　in　59　human　languages　and　one　whale　language；　a　12…minute　sound　essay　including　a　kiss；　a　baby's　cry；　and　an　EEG　record　of　the　meditations　of　a　young　woman　in　love；　116　encoded　pictures；　on　our　science；　our　civilization；　and　ourselves；　and　90　minutes　of　the　Earth's　greatest　hits—Eastern　and　Western；　classical　and　folk；　including　a　Navajo　night　chant；　a　Japanese　shakuhachi　piece；　a　Pygmy　girl's　initiation　song；　a　Peruvian　wedding　song；　a　3；000…year…old　position　for　the　ch'in　called　〃Flowing　Streams；〃　Bach；　Beethoven；　Mozart；　Stravinsky；　Louis　Armstrong；　Blind　Willie　Johnson；　and　Chuck　Berry's　〃Johnny　B。　Goode。〃

Space　is　nearly　empty。　There　is　virtually　no　chance　that　one　of　the　Voyagers　will　ever　enter　another　solar　system—and　this　is　true　even　if　every　star　in　the　sky　is　acpanied　by　planets。　The　instructions　on　the　record　jackets；　written　in　what　we　believe　to　be　readily　prehensible　scientific　hieroglyphics；　can　be　read；　and　the　contents　of　the　records　understood；　only　if　alien　beings；　somewhere　in　the　remote　future；　find　Voyager　in　the　depths　of　interstellar　space。　Since　both　Voyagers　will　circle　the　center　of　the　Milky　Way　Galaxy　essentially　forever；　there　is　plenty　of　time　for　the　records　to　be　found—if　there's　anyone　out　there　to　do　the　finding。

We　cannot　know　how　much　of　the　records　they　would　understand。　Surely　the　greetings　will　be　inprehensible；　but　their　intent　may　not　be。　（We　thought　it　would　be　impolite　not　to　say　hello。）　The　hypothetical　aliens　are　bound　to　be　very　different　from　us—independently　evolved　on　another　world。　Are　we　really　sure　they　could　understand　anything　at　all　of　our　message？　Every　time　I　feel　these　concerns　stirring；　though；　I　reassure　myself。　Whatever　the　inprehensibilities　of　the　Voyager　record；　any　alien　ship　that　finds　it　will　have　another　standard　by　which　to　judge　us。　Each　Voyager　is　itself　a　message。　In　their　exploratory　intent；　in　the　lofty　ambition　of　their　objectives；　in　their　utter　lack　of　intent　to　do　harm；　and　in　the　brilliance　of　their　design　and　performance；　these　robots　speak　eloquently　for　us。

But　being　much　more　advanced　scientists　and　engineers　than　we—otherwise　they　would　never　be　able　to　find　and　retrieve　the　small；　silent　spacecraft　in　interstellar　space—perhaps　the　aliens　would　have　no　difficulty　understanding　what　is　encoded　on　these　golden　records。　Perhaps　they　would　recognize　the　tentativeness　of　our　society；　the　mismatch　between　our　technology　and　our　wisdom。　Have　we　destroyed　ourselves　since　launching　Voyager；　they　might　wonder；　or　have　we　gone　on　to　greater　things？

Or　perhaps　the　records　will　never　be　intercepted。　Perhaps　no　one　in　five　billion　years　will　ever　e　upon　them。　Five　billion　years　is　a　long　time。　In　five　billion　years；　all　humans　will　have　bee　extinct　or　evolved　into　other　beings；　none　of　our　artifacts　will　have　survived　on　Earth；　the　continents　will　have　bee　unrecognizably　altered　or　destroyed；　and　the　evolution　of　the　Sun　will　have　burned　the　Earth　to　a　crisp　or　reduced　it　to　a　whirl　of　atoms。

Far　from　home；　untouched　by　these　remote　events；　the　Voyagers；　bearing　the　memories　of　a　world　that　is　no　more；　will　fly　on。




CHAPTER　10　　　SACRED　BLACK

　

　

Deep　sky　is；　of　all　visual　impressions；　the　nearest　akin　to　a　feeling。

—SAMUEL　TAYLOR　COLERIDGE；　NOTEBOOKS　（1805）

The　blue　of　a　cloudless　May　morning；　or　the　reds　and　oranges　of　a　sunset　at　sea；　have　roused　humans　to　wonder；　to　poetry；　and　to　science。　No　matter　where　on　Earth　we　live；　no　matter　what　our　language；　customs；　or　politics；　we　share　a　sky　in　mon。　Most　of　us　expect　that　azure　blue　and　would；　for　good　reason；　be　stunned　to　wake　up　one　sunrise　to　find　a　cloudless　sky　that　was　black　or　yellow　or　green。　（Inhabitants　of　Los　Angeles　and　Mexico　City　have　grown　accustomed　to　brown　skies；　and　those　of　London　and　Seattle　to　gray　ones—but　even　they　still　consider　blue　the　planetary　norm。）

And　yet　there　are　worlds　with　black　or　yellow　skies；　and　maybe　even　green。　The　color　of　the　sky　characterizes　the　world。　Plop　me　down　on　any　planet　in　the　Solar　System；　wsithout　sensing　the　gravity；　without　glimpsing　the　ground；　let　me　take　a　quick　look　at　the　Sun　and　sky；　and　I　can；　I　think；　pretty　well　tell　you　where　I　am。　That　familiar　shade　of　blue；　interrupted　here　and　there　by　fleecy　white　clouds；　is　a　signature　of　our　world。　The　French　have　an　expression；　sacre…bleu！；　which　translates　roughly　as　〃Good　heavens！〃*　Literal