pale blue dot -carl sagan-第17章

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！



Galileo　is　a　NASA　spacecraft　designed　to　explore　the　giant　planet　Jupiter；　its　moons；　and　its　rings。　It's　named　after　the　heroic　Italian　scientist　who　played　so　central　a　role　in　toppling　the　geocentric　pretension。　It　is　he　who　first　saw　Jupiter　as　a　world；　and　who　discovered　its　four　big　moons。　To　get　to　Jupiter；　the　spacecraft　had　to　fly　close　by　Venus　（once）　and　the　Earth　（twice）　and　be　accelerated　by　the　gravities　of　these　planets—otherwise　there　wasn't　enough　oomph　to　get　it　where　it　was　going。　This　necessity　of　trajectory　design　permitted　us；　for　the　first　time；　to　look　systematically　at　the　Earth　from　an　alien　perspective。

Galileo　passed　only　960　kilometers　（about　600　miles）　above　the　Earth's　surface。　With　some　exceptions—including　pictures　showing　features　finer　than　1　kilometer　across；　and　the　images　of　the　Earth　at　night—much　of　the　spacecraft　data　described　in　this　chapter　were　actually　obtained　by　Galileo。　With　Galileo　we　were　able　to　deduce　an　oxygen　atmosphere；　water；　clouds；　oceans；　polar　ice；　life；　and　intelligence。　The　use　of　instruments　and　protocols　developed　to　explore　the　planets　to　monitor　the　environmental　health　of　our　own—something　NASA　is　now　doing　in　earnest—was　described　by　the　astronaut　Sally　Ride　as　〃Mission　to　Planet　Earth。〃

Other　members　of　the　NASA　scientific　team　who　worked　with　me　on　Galileo's　detection　of　life　on　Earth　were　Drs。　W。　Reid　Thompson；　Cornell　University；　Robert　Carlson；　JPL；　Donald　Gurnett；　University　of　Iowa；　and　Charles　Hord；　University　of　Colorado。

Our　success　in　detecting　life　on　Earth　with　Galileo；　without　making　any　assumptions　beforehand　about　what　kind　of　life　it　must　be；　increases　our　confidence　that　when　we　fail　to　find　life　on　other　planets；　that　negative　result　is　meaningful。　Is　this　judgment　anthropocentric；　geocentric；　provincial？　I　don't　think　so。　We're　not　looking　only　for　our　kind　of　biology。　Any　widespread　photosynthetic　pigment；　any　gas　grossly　out　of　equilibrium　with　the　rest　of　the　atmosphere；　any　rendering　of　the　surface　into　highly　geometrized　patterns；　any　steady　constellation　of　lights　on　the　night　hemisphere；　any　non…astrophysical　sources　of　radio　emission　would　betoken　the　presence　of　life。　On　Earth　we　have　found　of　course　only　our　type；　but　many　other　types　would　have　been　detectable　elsewhere。　We　have　not　found　them。　This　examination　of　the　third　planet　strengthens　our　tentative　conclusion　that；　of　all　the　worlds　in　the　Solar　System；　only　ours　is　graced　by　life。

We　have　just　begun　to　search。　Maybe　life　is　hiding　on　Mars　or　Jupiter；　Europa　or　Titan。　Maybe　the　Galaxy　is　filled　with　worlds　as　rich　in　life　as　ours。　Maybe　we　are　on　the　verge　of　making　such　discoveries。　But　in　terms　of　actual　knowledge；　at　this　moment　the　Earth　is　unique。　No　other　world　is　yet　known　to　harbor　even　a　microbe；　much　less　a　technical　civilization。




CHAPTER　6　　　THE　TRIUMPH　OF　VOYAGER

　

　

They　that　go　down　to　the　sea　in　ships；　that　do　business　in　great　waters；

these　see　the　works　of　the　Lord；　and　his　wonders　in　the　deep。

—PSALMS；　107　（CA。　150　B。C）

The　visions　we　offer　our　children　shape　the　future。　It　matters　what　those　visions　are。　Often　they　bee　self…fulfilling　prophecies。　Dreams　are　maps。

I　do　not　think　it　irresponsible　to　portray　even　the　direst　futures；　if　we　are　to　avoid　them；　we　must　understand　that　they　are　possible。　But　where　are　the　alternatives？　Where　are　the　dreams　that　motivate　and　inspire？　We　long　for　realistic　maps　of　a　world　we　can　be　proud　to　give　to　our　children。　Where　are　the　cartographers　of　human　purpose？　Where　are　the　visions　of　hopeful　futures；　of　technology　as　a　tool　for　human　betterment　and　not　a　gun　on　hair　trigger　pointed　at　our　heads？

NASA；　in　its　ordinary　course　of　doing　business；　offers　such　a　vision。　But　in　the　late　1980s　and　early　'90s；　many　people　saw　the　U。S。　space　program　as；　instead；　a　succession　of　catastrophes—seven　brave　Americans　killed　on　a　mission　whose　main　function　was　to　put　up　a　munications　satellite　that　could　have　been　launched　at　less　cost　without　risking　anybody；　a　billion…dollar　telescope　sent　up　with　a　bad　case　of　myopia；　a　spacecraft　to　Jupiter　whose　main　antenna—essential　for　returning　data　to　Earth—did　not　unfurl；　a　probe　lost　just　as　it　was　about　to　orbit　Mars。　Some　people　cringe　every　time　NASA　describes　as　exploration　sending　a　few　astronauts　200　miles　up　in　a　small　capsule　that　endlessly　circles　the　Earth　and　goes　nowhere。　pared　to　the　brilliant　achievements　of　robotic　missions；　it　is　striking　how　rarely　fundamental　scientific　findings　emerge　from　manned　missions。　Except　for　repairing　ineptly　manufactured　or　malfunctioning　satellites；　or　launching　a　satellite　that　could　just　as　well　have　been　sent　up　in　an　unmanned　booster；　the　manned　program　has；　since　the　1970s；　seemed　unable　to　generate　acplishments　mensurate　with　the　cost。　Others　looked　at　NASA　as　a　stalking　horse　for　grandiose　schemes　to　put　weapons　into　space；　despite　the　fact　that　an　orbiting　weapon　is　in　many　circumstances　a　sitting　duck。　And　NASA　showed　many　symptoms　of　an　aging；　arteriosclerotic；　overcautious；　unadventurous　bureaucracy。　The　trend　is　perhaps　beginning　to　be　reversed。

But　these　criticisms—many　of　them　surely　valid—should　not　blind　us　to　NASA　triumphs　in　the　same　period：　the　first　exploration　of　the　Uranus　and　Neptune　systems；　the　in…orbit　repair　of　the　Hubble　space　telescope；　the　proof　that　the　existence　of　galaxies　is　patible　with　the　Big　Bang；　the　first　close…up　observations　of　asteroids；　mapping　Venus　pole　to　pole；　monitoring　ozone　depletion；　demonstrating　the　existence　of　a　black　hole　with　the　mass　of　a　billion　suns　at　the　center　of　a　nearby　galaxy；　and　a　historic　mitment　to　joint　space　endeavors　by　the　U。S。　and　Russia。

There　are　far…reaching；　visionary；　and　even　revolutionary　implications　to　the　space　program。　munications　satellites　link　up　the　planet；　are　central　to　the　global　economy；　and；　through　television；　routinely　convey　the　essential　fact　that　We　live　in　a　global　munity。　Meteorological　satellites　predict　the　weather；　save　lives　in　hurricanes　and　tornados；　and　avoid　many　billions　of　dollars　in　crop　losses　every　year。　Military…reconnaissance　and　treaty…verification　satellites　make　nations　and　the　global　civilization　more　secure；　in　a　world　with　tens　of　thousands　of　nuclear　weapons；　they　calm　the　hotheads　and　paranoids　on　all　sides；　they　are　essential　tools　for　survival　on　a　troubled　and　unpredictable　planet。

Earth…observing　satellites；　especially　a　new　generation　soon　to　be　deployed；　monitor　the　health　of　the　global　environment：　greenhouse　warming；　topsoil　erosion；　ozone　layer　depletion；　ocean　currents；　acid　rain；　the　effects　of　floods　and　droughts；　and　new　dangers　we　haven't　yet　discovered。　This　is　straightforward　planetary　hygiene。

Global　positioning　systems　are　now　in　place　so　that　your　locale　is　radio…triangulated　by　several　satellites。　Holding　a　small　instrument　the　size　of　a　modern　shortwave　radio；　you　can　read　out　to　high　precision　your　latitude　and　longitude。　No　crashed　airplane；　no　ship　in　fog　and　shoals；　no　driver　in　an　unfamiliar　city　need　ever　be　lost　again。

Astronomical　satellites　peering　outward　from　Earth's　orbit　observe　with　unsurpassed　clarity—studying　questions　ranging　from　the　possible　existence　of　planets　around　nearby　stars　to　the　origin　and　fate　of　the　Universe。　Planetary　probes　from　close　range　explore　the　gorgeous　array　of　other　worlds　in　our　solar　system　paring　their　fates　with　ours。

All　of　these　activities　are　forward…looking；　hopeful；　stirring　and　cost…effective。　None　of　them　requires　〃manned〃*　spaceflight。　A　key　issue　facing　the　future　of　NASA　and　addressed　in　this　book　is　whether　the　purported　justifications　for　human　spaceflight　are　coherent　and　sustainable。　Is　it　worth　the　cost？

*　Since　women　astronauts　and　cosmonauts　of　several　nations　have　flown　in　space；　〃manned〃　is　just　flat…out　incorrect。　I've　attempted　to　find　an　alternative　to　this　widely　used　term；　coined　in　a　more　unselfconsciously　sexist　age。　I　tried　〃crewed〃　for　a　while；　but　in　spoken　language　it　lends　itself　to　misunderstanding。　〃Piloted〃　doesn't　work；　because　even　mercial　airplanes　have　robot　pilots。　〃Manned　and　womanned〃　is　just；　but　unwieldy。　Perhaps　the　best　promise　is