英语文反抄袭年度,小学英语教学文评比的通知

本文是一篇纯英语论文范文,纯英语类专升本毕业论文开题报告,关于英语文反抄袭年度,小学英语教学文评比的通知相关学年毕业论文范文。适合纯英语及托福及小马方面的的大学硕士和本科毕业论文以及纯英语相关开题报告范文和职称论文写作参考文献资料下载。

托福阅读纯英语论文文献1

小马过河为大家准备了"托福阅读纯英语论文文献1",供各位备考托福的考生们参考使用,来提高自己的托福成绩！免费咨询:400-0123-267

heCassini-HuygensMission:LiftingtheVeilofSecrecy

Itisdifficulttosaywhatisimpossible,forthedreamofyesterdayisthehopeoftodayandrealityoftomorrow.-RobertGoddard

Introduction

OnJuly1st,2004,theinternationalCassini-HuygensMissionspacecraftenteredintoorbitaroundtheplaSaturn.TheCassinispacecraftwillremaininSaturn'sorbitforfouryearstoprobeitsrings,itsatmosphere,anditoons,amongotherthings.OnChristmas2004,theHuygensprobe,attachedtotheCassinispacecraft,willdisengagefromCassiniandisscheduledtolandonoraboutJanuary14,2005,onSaturn'slargestmoon,Titan.Ifsuccesul,thiswouldmarkoneofmankind'sgreatestachievements.Titan,thesecondlargestmooninthesolarsystem,isofgreatinteresttoscientistsbecauseitistheonlymoonknowntohecloudsandamysteriouspla-likeatmosphere.Titan'satmosphereappearsasanopaqueorangehaze,obscuringitssurfacefromview,andveilingitssecrets.TheCassini-HuygensMissionseekstoliftthatveilofsecrecyduringitour-yeartourofSaturn,itoons,anditagosphere.ScientistshopetogainabetterunderstandingofTitan'ssurface,atmosphere,andchemicalposition,toperhapsshedsomelightaboutwhatprimordialEarthmighthebeenlikebillionsofyearsago.1

I.ThePlaSaturnanditsNaturalSatellites

InRomanmythology,Saturnisthegodofagriculture.TheassociatedGreekgod,Cronus,wasthesonofUranusandGaiaandthefatherofZeus(Jupiter).SaturnistherootoftheEnglishword"Saturday"(i.e.,Saturn'sday).

TheplaSaturnhasbeenknownsinceprehistorictimes.TheItalianastronomer,physicistandmathematicianGalileoGalilei(1564-1642)wasthefirsttoobserveitwithatelescopein1610,henoteditsoddappearancebutwasconfusedbyit.ThisconfusioncontinuedthroughearlyobservationsofSaturn,whichwereplicatedbythefactthattheEarthpassesthroughtheplaneofSaturn'sringseveryfewyearsasSaturnmovesinitsorbit.AlowresolutionimageofSaturnthereforechangesdrastically.Itwasnotuntil1659thattheDutchastronomerChristiaanHuygens(1629-1695)correctlyinferredthegeometryoftherings.Saturn'sringsremaineduniqueintheknownsolarsystemuntil1977whenveryfaintringswerediscoveredaroundtheplaUranus(andshortlythereafteraroundtheplasJupiterandNeptune).

SaturnisthesixthplafromtheSunandisthesecondlargestinthesolarsystem,withanequatorialdiameterof119,300kilometers(74,130miles).SaturnwairstvisitedbythePioneer11spacecraftin1979,muchofwhatisknownabouttheplaisduetotheVoyager1andVoyager2spacecraftexplorationsin1980-81.Visiblyflattenedatthepolesasresultoftheveryfastrotationonitsaxis,Saturnhasaday10hours,39minuteslong,andtheplatakes29.5EarthyearstorevolveabouttheSun.Theatmosphereisprimarilyposedofhydrogen(about97percent)withallamountsofhelium(aboutercent)andmethane.BecauseSaturnistheonlyplalessdensethanwater(about30percentless),ifalargeenoughbodyofwatercouldbefound,Saturnwouldfloatinit.Thepla'shazyyellowhueiarkedbybroadatmosphericbandingsimilarto,butfainterthan,thatfoundonJupiter.

ThewindblowsathighspeedsonSaturn,mostlyinaneasterlydirection.Neartheequator,itreachesvelocitiesof500meterspersecond(1100milesanhour).Thestrongestwindsarefoundneartheequator,andthevelocityfallsoffuniformlyathigherlatitudes.Atlatitudesgreaterthan35degrees,windsalternateeastandwestaslatitudeincreases.

Saturn'sringsystemmakestheplaoneofthemostbeautifulobjectsinthesolarsystem.Theringsaredividedintosevenmajordivisionswithalphabeticdesignatorsintheorderofdiscovery.FromtheinnermostringtotheoutermostringthedesignatorsareD,C,B,A,F,GandE.Eachmajordivisioniurthersubdividedintothousandsofindividualringlets.TheFandGringsareverythinanddifficulttoseewhiletheA,B,andCringsarebroadandquitevisible.Theringsystemhasvariousgaps,themostnotableofwhichistheCassiniDivision,whichseparatestheAandBrings.TheFrench-ItalianastronomerJeanDominique(GiovanniDomenico)Cassini(1625-1712)discoveredthisdivisionin1675.BetweentheAandFringsliestheKeeler(Encke)gap,whichincludesthebrightAandBringsandafainterCring.TheEncke(pronouncedEN-kee)Division,whichsplitstheARing,isnamedafterJohannEncke,whoiscreditedwithdiscoveringitin1837,butmostlikelyneversawit.TheVoyagerpicturesshowthefourD,E,F,andGfaintrings.Spaceprobesheshownthatthemainringsarereallymadeupofalargenumberofnarrowringlets.Theoriginoftheringsisobscure,itisthoughtthattheymayhebeenformedfromlargermoonsthatwereshatteredbyimpactsofets,andmeteoroids.Theringpositionisnotdefinitivelyknown,buttheringsdoshowasignificantamountofwater.Theymaybeposedoficebergsand/orsnowballswhosesizeayrangefromafewcentimeterstoafewmeters.Muchoftheelaboratestructureofsomeoftheringsisduetothegritationaleffectsofnearbynaturalsatellites(moons).

Radialspoke-likefeaturesinthebroadB-ringwerealsofoundbytheVoyagerspacecraft.Thefeaturesarebelievedtobeposedoffinedust-sizeparticles.Thespokeswereobservedtoformanddissipateinthetime-lapseimagestakenbytheVoyagers.Whileelectrostaticchargingmaycreatespokesbylevitatingdustparticlesabovethering,theexactcauseoftheformationofthespokesisnotwellunderstood.2

Toanearthling,Saturn'sphysicalcharacteristicsaremind-bogglinglylarge.SaturneandistancefromtheSunis1,429,400,000kmor9.54AstronomicalUnits(AU)(AnAUisthemeandistancefromtheEarthtotheSun).Saturn'sdiameteris120,536kmatitsequatoranditassis5.68x1026kg,or9.5181Earthmasses.Asofnow,Saturnhasatotalof31namedmoons(ornaturalsatellites).The31standlatestnamedmoon(S/2003S1)waoundonFebruary5,2003,previously,twoasyetunnamedmoonswerediscoveredin2004.Saturn'sdensityis0.69gramspercubiccentimeter,anditeanorbitalvelocity(themeanspeedwithwhichittrelsaroundtheSun)is9.67kilometerspersecond(9.67km/s),whichisaround6miles/s.ThetiltangleofSaturn'saxisofrotationis25.33deg.Saturn'satmosphericpressureis1.4bars,iteancloudtemperatureis-125degreesC(-125C).ItslargestmoonTitan,witharadiusof2575.5+/-2km,wasdiscoveredbyChristiaanHuygensin1655.Itournextlargestmoons,indescendingorder,areRhea(764+/-4kmradius),Iapetus(730kmradius)Dione(559+/-5kmradius),andTethys(529.9+/-1.5kmradius).AllfourofthosemoonswerediscoveredbyGiovanniCassiniin1672(Rhea),1671(Iapetus),andin1684(DioneandTethys).3

TheCassini-HuygensMissionisintendedtoprovideabetterunderstandingoftheplaSaturn,itamousrings,itagosphere,itsprincipalmoonTitan,anditsothermoonsor"icysatellites."Alongwithextensivepreparation,planningandtrackingthroughoutthemission,scienceobjectivesaredividedintotwoparts:thegoalsenroutetotheringedpla,andthenthoseoccuringafterthespacecraftarrives.

ToensureallinstrumentsonboardthespacecraftareworkingproperlyfortheupingtourofSaturn,checkswereperformedviaremotecontrolatlaunchtimeaswellasafter14monthsinspace.Thisincludesroutineinstrumentmaintenance,GritationalWeExperiments,instrumentcalibrations,andconjunctio

本文是一篇纯英语论文范文,纯英语类专升本毕业论文开题报告,关于英语文反抄袭年度,小学英语教学文评比的通知相关学年毕业论文范文。适合纯英语及托福及小马方面的的大学硕士和本科毕业论文以及纯英语相关开题报告范文和职称论文写作参考文献资料下载。

The12instrumentsonboardtheCassiniSpacecraftorbiterand6instrumentsonboardtheHuygensProbearedesignedtoperformin-situ(on-site)studiesofelementsofSaturn,itsatmosphere,moons,rings,andmagosphere.Theinstrumentswillstudytemperaturesinvariouslocations,plaalevels,neutralandchargedparticles,positionsofsurfaces,atmospheresandrings,solarwind,andevendustgrainsintheSaturnsystem.Otherinstrumentswillperformspectralmappingforhigh-qualityimagesofthepla,itoonsandrings.5

ThescienceobjectiveorSaturn'sringsare(1)tostudytheirconfigurationandthedynamicprocessesresponsiblefortheringstructure,(2)tomapthepositionandsizedistributionoftheringmaterial,(3)toinvestigatetheinterrelationofSaturn'sringsandmoons,includingmoonsimbeddedwithintherings,(4)todeterminethedistributionofdustandmeteoroiddistributioninthevicinityoftherings,and(5)tostudytheinteractionsbetweentheringsandSaturn'agosphere,ionosphere,andatmosphere.ionosphereandthepla'agicfield,(5)todeterminetheposition,heatflux,andradiationenvironmentpresentduringSaturn'ormationandevolution,and(6)toinvestigatethesourcesandnatureofSaturn'slightning.7

TitanisatimevaultinsofarasitsuniqueenvironmentandthickatmospheremayresemblethatofEarthsomeseveralbillionyearsago,beforelifeasweknowitbeganpumpingoxygenintoouratmosphere.

Titan'satmosphereiadeupprimarilyofnitrogen,whichappearsasanopaqueorangehaze,obscuringitssurfacefromview.Titanisthesecondlargestmooninthesolarsystem,afterJupiter'oonGanymede.At5150km(3200miles,paredto2160mileorEarth'oon)indiameter,TitanislargerthaneachoftheplasMercuryandPluto.TitanorbitsSaturnatadistancefromtheplaof1,222,000km(759,478miles),taking15.9daystopleteonerevolution.Itassis1.34x1023kg,itseragedensityis1.88g/cubiccm,anditssurfacetemperatureis95K(i.e.,-178Cor-288F).8

ThroughongoingobservationromEarthaswellasdatacollectedbythePioneerandVoyagerspacecraft,scientistsnowknowthatTitan'satmosphereisover95percentnitrogen,whileonly5percentisposedofmethane,cyanide,andotherhydrocarbons.

Titanistheonlyknownmooninthesolarsystemwithathickatmosphere,10timesthickerthanEarth's.Exceptforsomeclouds,Earth'ssurfaceisvisiblefromspace.ButonTitan,athickhazeat200km(120miles)abovethesurfaceobscurestheentiremoonfromview.TheatmosphereisthickenoughsothatapersonstandingonTitan'ssurfaceinthedaytimewouldexperiencealevelofdaylightequivalentto1/1000ththedaylightonEarth'ssurface.Thisparisonnotonlytakesintoaccounttheatmosphere'sthickness,butalsoTitan'sgreaterdistancefromtheSun.Noheless,lightlevelsonTitan'ssurfaceare350timesbrighterthanmoonlightonEarthunderafullmoon.9

Titan'ssurfaceisshroudedfromview,andsoconditionsonthesurfacearenotwellunderstood.OurknowledgeeromrecentimagesusingtheHubbleSpaceTelescope.BrightnessvariationsareevidentinHubbledata,includingalargecontinent-sizedregiononTitan'ssurface.Scientistsbelievethisbrightnessdifferenceispartlyduetodifferentchemicalpositionsonitssurface,whichcouldmeanthatTitanhousesoceansofliquidhydrocarbons.

BybiningresultromtheCassini-HuygensMissionwithEarth-basedastronomicalobservation,Hubbledata,laboratoryexperimentsandputermodels,scientistshopetoanswerbasicquestionsregardingtheoriginandevolutionofthisintriguingsatellite,suchaswhyitdevelopedanatmospheresimilartothatofEarths,whereastheothermoonsdidn't,andwhetherTitanevolvedonitsownorwasejectedfromSaturnitself.10

FortheCassini-HuygensMissionthescientificobjectiveorTitanare(1)todeterminethemostabundantelements,andmostlikelyscenarioortheformationandevolutionofTitananditsatmosphere,(2)todeterminetherelativeamountsofdifferentponentsoftheatmosphere,(3)toobserveverticalandhorizontaldistributionsoftracegases,searchforplexmolecules,investigateenergysourceoratmosphericchemistry,determinetheeffectsofsunlightonchemicalsinthestratosphere,andstudytheformationandpositionofaerosols,(4)tomeasurewindsandglobaltemperatures,investigatecloudphysics,generalcirculationandseasonaleffectsinTitan'satmosphere,searchforlightning,(5)todeterminethephysicalstate,topographyandpositionofTitan'ssurfaceandcharacterizeitsinternalstructure,(6)toinvestigateTitan'supperatmosphere,itsionizationanditsroleasasourceofneutralandionizedmaterialforthemagosphereofSaturn,and(7)todeterminewhetherTitan'ssurfaceisliquidorsolid,andanalyzetheevidenceofabrightcontinentasindicatedinHubbleimagestakenin1994.11

CassiniandPhoebe

Discoveredmorethan100yearsagobyAmericanastronomerWilliamPickering,Phoebe,oneofSaturn'stiniestnamedmoons,isasourceofextensivescientificinterest.Roughlysphericalandwithadiameterof220km(about136.7miles),whichisequaltoaboutone-fifteenthofthediameterofEarth'oon,PhoeberotatesonitsaxiseveryninehoursandpletesafullorbitaroundSaturninabout18months.Itsirregularellipticalorbitisinclinedapproximately30degreestowardSaturn'sequator.Phoebe'sorbitisalsoretrograde,whichmeansitgoesaroundSaturnintheoppositedirectionofmostothermoons,aswellasofmostotherobjectsinthesolarsystem.Itseragedistancefromtheringedplais13millionkm(about8millionmiles),whichisalmostfourtimeartherawayfromSaturnthanitsnearestneighbor,themoonIapetus.PhoebeandIapetusaretheonlymajormoonsintheSaturnregionthatdonotorbitclosetotheplaneofSaturn'sequator.

OnJune11,2004,afewweeksbeforeenteringtheorbitofSaturn,theCassinispacecraftflewbyPhoebeandbeganitslandmarkscientificmission.ThedistancefromwhichimagesofPhoebeweretakenisradicallydifferentfromtheearly1980s,whenVoyager2embarkedonitslegendarytourofthesolarsystem.Then,Voyager2'scamerassnappedimagesofPhoebefromabout2.2millionkm(about1.4millionmiles)away.Cassini,ontheotherhand,snappedimageromamere2000km(about1240miles)fromthemoon'ssurface.Inaddition,thankstosignificanttechnologicalimprovementsthroughoutthepast20years,Cassini'scamerasarenotonlyfarallerthan,butalsofarsuperiorinimagequalityto,theirearliercounterparts.UnlikemostmajormoonsorbitingSaturn,Phoebeisverydarkandreflectsonly6percentofthesunlightitreceives.Itsdarknessandirregular,retrogradeorbitsuggestthatPhoebeiostlikelyacapturedobject,whichisdefinedasacelestialbodythatistrappedbythegritationalpullofamuchbiggerbody,generallyapla.Phoebe'sdarknessinparticularsuggeststhattheallmooneromtheoutersolarsystem,aregionknownastheKuiperBelt,wheremanycelestialbodiescontaindarkmaterial.

SomescientiststhinkPhoebecouldbeacapturedCentaur,aKuiperBeltobjectthatmigratedintotheinnersolarsystem.CentaursarefoundbetweentheasteroidbeltandtheKuiperBelt,andareconsideredtobeintermediatebodies.IfPhoebeisindeedaCentaur,imagesandscientificdatatakenbytheCassinispacecraftwillgivescientiststhefirstintensiveopportunitytostudyaKuiperBeltobject.

KuiperBeltobjectsareofextremeinteresttoscientistsbecausetheyarebelievedtobeprimordial,thatis,theyappeartodatebacktotheformationofthesolarsystem.Knownasthe"buildingblocks"ofthesolarsystem,KuiperBeltobjectsexistaragmentsthatwereneverdrawnt

本文是一篇纯英语论文范文,纯英语类专升本毕业论文开题报告,关于英语文反抄袭年度,小学英语教学文评比的通知相关学年毕业论文范文。适合纯英语及托福及小马方面的的大学硕士和本科毕业论文以及纯英语相关开题报告范文和职称论文写作参考文献资料下载。

Becauseofitsallsizeandpoorreflectiveproperties,Phoebemightnothegeneratedenoughheatsinceitormationtoalteritsoriginalchemicalposition.Thisisanothermajorfactorthatincreasesthescientificvalueofthestudyofthiysteriouoon.13

SummaryofKeyDatesandHighlightsoftheCassini-HuygensSaturnTour:

KeydatesoftheSaturnTourinclude:

June11,2004(19:32UTC):FlybyofthefurthestmoonorbitingSaturn,Phoebe,atanaltitudeof2000km(1243miles).July1,2004:CrossingofSaturn'sRingPlaneduringthespacecraft'scriticalSaturnOrbitInsertionsequence.December25,2004(02:00UTC)HuygensprobeseparateromtheCassiniorbiterandbeginsits21-dayjourneytoTitan.December25countsasdayoneandJanuary14isday21.January14,2005:HuygensbeginsitsdescentthroughTitan'scloudyatmosphere,whereitlandsonthesurfaceabouttwoandone-halfhourslater.TheprobeisscheduledtoencountertheupperfringesofTitan'satmosphereat09:00UTC.14

HighlightsoftheSaturnTourinclude:74orbitsofSaturn,45closeflybysofTitan,eightclose"targeted"flybysofothersatellites:threeofEnceladus,andoneeachofPhoebe,Hyperion,Dione,Rhea,andIapetus,30additionalsatelliteflybysatdistanceslessthan100,000km(about62,100miles),manySaturnandringoccultationopportunities,andone"Titan180-degree"orbittraner.15

III.TheStorySoFarAway

Phoebe

NASA'sCassinispacecraftsuccesullypleteditirstcloseflybyofamoonofSaturnonFriday,June11,2004,whenthespacecraftcapturedimagesofthemoonPhoebe.Detailedimagesrevealedaheilycrateredsurfacethathasastronomersdebatingthesatellite'sorigins.Themostdetailedimagereleasedsofarshowsatinyworldriddledwithancientpockmarks,butwithgreatvariationsofsurfacebrightness.Phoebeingeneralisverydark,butcloseinspectionrevealedareassobrightthattheywerewashedoutinthepicture.Thesharpclearimagesshowedmanygeologicalfeatures.Thoughitistooearlytosay,researchersbelievecloserinspectionofthepicturesofPhoebecouldrevealittobeindeedaKuiperBeltobject.

Thehighestresolutionimagesofarreleasedshowsacraterneartherighthandedgewithbrightraysthatextendfromitscenter.Thissuggeststhatdarkmaterialcoatstheoutsideofwhatmaybeapredominantlyicybody.KuiperBeltobjects,moresothanasteroids,arethoughttoconsistlargelyofice.ThelargecratershealsoledtospeculationthatPhoebe,thelargestofSaturn'soutermoons,mightbetheparentoftheother,muchallerbackward-orbitingoutermoonsofSaturn."Lookingatthosebig50-km(31-mile)craters,onehastowonderwhethertheirimpactejectamightbetheothertinymoonsthatorbitSaturnonpathuchlikePhoebe's,"saidJosephBurns,animagingteammemberandprofessoratCornellUniversity.16

FirstimageromtheCassiniflybyofPhoeberevealascarred,crateredoutpostwithanancientandmysteriouspast,andhugevariationinsurfacebrightness

Source:NASA/JPL/SpaceScienceInstitute

Saturn'sShadowandTitan'sGlow

TheCassinispacecrafthasdetectedlightningandanewradiationbeltatSaturn,andaglowaroundthepla'slargestmoon,Titan.Thespacecraft'sradioandplaawescienceinstrumentdetectedradiowesgeneratedbylightning.ThecracklingandpoppingsoundsdetectedarethesameasonehearswhenlisteningtoanAMradiobroadcastduringathunderstorm,accordingtoDr.BillKurth,deputyprincipalinvestigatorontheradioandplaaweinstrument,UniversityofIowa,IowaCity.Dr.Kurthalsosaysthat,"Thesestormsaredramaticallydifferentthanthoseobserved20yearsago."

Cassinifindsradioburstromthislightningarehighlyepisodic.Therearelargevariationsintheoccurrenceoflightningfromdaytoday,sometimeswithlittleornolightning,suggestinganumberofdifferent,possiblyshort-livedstorms,atmid-tohighlatitudes.Voyagerobservedlightningfromanextendedstormsystematlowlatitudes,whichlastedformonthsandappearedhighlyregularfromonedaytothenext.Thedifferenceinstormcharacteristicayberelatedtoverydifferentshadowingconditionsinthe1980sthancurrently.DuringtheVoyagertimeperiodwhenlightningwairstobserved,theringscasterydeepshadownearSaturn'sequator.Asaresult,theatmosphereinanarrowbandwaspermanentlyinshadow,**itcold,bycontrastwiththeadjacenthottestbandinSaturn'satmosphere.Turbulencebetweenthehotandcoldregionscouldheledtolong-livedstorms.However,duringCassini'sapproachandentryintoSaturn'sorbit,itwassummerinthesouthernhemisphereandtheringshadowwasdistributedwidelyoveralargeportionofthenorthernhemisphere.Thiscausesthehottestandcoldestregionstobefarapart.

AmajorfindingofthemagosphericimaginginstrumentisthediscoveryofanewradiationbeltjustaboveSaturn'scloudtops,uptotheinneredgeoftheD-ring.ThisisthefirsttimethatanewSaturnianradiationbelthasbeendiscoveredwithremotesensing.Thisnewradiationbeltextendsaroundthepla.ItwasdetectedbytheemissionoffastneutralatomscreatedasitagicallytrappedionsinteractwithgascloudslocatedplawardoftheD-ring.Withthisdiscovery,theradiationbeltsareshowntoextendfarclosertotheplathanpreviouslyknown.

"ThisnewradiationbelthadeludeddetectionbypreviousvisitstoSaturn,"accordingtoDr.DonaldG.Mitchell,instrumentscientistforthemagosphericimaginginstrumentattheJohnsHopkinsUniversityAppliedPhysicsLaboratory,Laurel,MD."Withitsdiscoveryweheseensomethingthatwedidnotexpect,thatradiationbeltparticlescan'hop'overobstructionslikeSaturn'srings,withoutbeingabsorbedbytheringsintheprocess."

AorTitan,Cassini'svisualandinfraredmappingspectrometercaptureditglowingbothdayandnight,poweredbyemissionrommethaneandcarbonmonoxidegasesinthemoon'sextensive,thickatmosphere."NotonlyisTitanputtingonagreatlightshowbutitisalsoteachinguoreaboutitsdenseatmosphere,"saysDr.KevinBaines,scienceteammemberforthevisualandinfraredmappingspectrometeratJPL."Whatisamazingisthatthesizeofthisgloworemissionofgasesisasixththediameterofthepla,"headds.

TheSun-illuminatedfluorescentglowofmethanethroughoutTitan'supperatmosphere,revealingtheatmosphere'simmensethicknessandextendingmorethan700km(435miles)abovethesurface,wasexpected.However,thenighttimeglow,persistentlyshiningoverthenightsideofTitan,initiallysurprisedscientists.Titanglowsthroughoutthenear-infraredspectrum.17

TwoNewMoons

TheCassinispacecrafthasuncoveredtwomoons,whichmaybetheallestbodiessofarseenaroundSaturn:approximately3km(2miles)and4km(2.5miles)across.Themoons,located194,000km(120,000miles)and211,000km(131,000miles)fromthepla'scenter,arebetweentheorbitsoftwootherSaturnianmoons,MimasandEnceladus.TheyareprovisionallynamedS/2004S1andS/2004S2.ThefirstmaybeanobjectspottedinasingleimagetakenbyNASA'sVoyagerspacecraft23yearsago,calledatthattimeS/1981S14.

ThemoonswerefirstseenbyDr.SebastienCharnoz,aplaarydynamicistworkingwithDr.AndreBrahic,imagingteammemberattheUniversityofParis.TheallestpreviouslyknownmoonsaroundSaturnareabout20km(12miles)across.ScientistsexpectedthatmoonsasallasS/2004S1andS/2004S2mightbefoundwithingapsintheringsandperhapsneartheFring,sotheyweresurprisedtodiscovertheseal

本文是一篇纯英语论文范文,纯英语类专升本毕业论文开题报告,关于英语文反抄袭年度,小学英语教学文评比的通知相关学年毕业论文范文。适合纯英语及托福及小马方面的的大学硕士和本科毕业论文以及纯英语相关开题报告范文和职称论文写作参考文献资料下载。

MoreRingsandMoreObjects

ScientistsexaminingSaturn'scontortedFring,whichhasbaffledthemsinceitsdiscovery,hefoundoneallbody,possiblytwo,orbitingintheregion,andaringofmaterialassociatedwithSaturn'oonAtlas.AallobjectwasdiscoveredmovingneartheoutsideedgeoftheFring,interiortotheorbitofSaturn'oonPandora,inimagestakenonJune21,2004,justdaysbeforeCassiniarrivedatSaturn.Dr.CarlMurray,imagingteammemberatQueenMary,UniversityofLondon,statesthat,"InoticedthisbarelydetectableobjectskirtingtheouterpartoftheFring."Murray'sgroupatQueenMarythencalculatedanorbitfortheobject.

Scientistscannotyetdefinitivelysayiftheobjectisamoonoratemporaryclump,i.e.,arelativelyshort-livedconglomerationofmattersuchasrocksordustthatisswepttogetherbygrityorbyrotationalforcesandwhichmaygivetheappearanceofamoon-likebody.Ifitisamoon,itsdiameterisestimatedat4-5km(2-3miles),anditislocated1000km(620miles)fromtheFring,Saturn'soutermostring.Itisatadistanceofapproximately141,000km(about86,000miles)fromthecenterofSaturnandwithin300km(190miles)oftheorbitofthemoonPandora.TheobjecthasbeenprovisionallynamedS/2004S3.

Scientistsarenotsureiftheobjectisalone.Thisisbecauseofresultromasearchthroughotherimagesthatmightcapturetheobjecttopindownitsorbit.ThesearchbyDr.JosephSpitale,aplaaryscientistworkingwithteamleaderDr.CarolynPorcoattheSpaceScienceInstituteinBoulder,CO,revealedsomethingstrange.Spitalesays,"WhenIwenttolookforadditionalimagesofthisobjecttorefineitsorbit,Ifoundthataboutfivehoursafterfirstbeingsighted,itseemedtobeorbitinginteriortotheFring....IfthisisthesameobjectthenithasanorbitthatcrossestheFring,whichmakesitastrangeobject."Becauseofthepuzzlingdynamicalimplicationsofhingabodythatcrossesthering,theinnerobjectsightedbySpitaleispresentlyconsideredaseparateobjectwiththetemporarydesignationS/2004S4.S4isroughlythesamesizeasS3.IntheprocessofexaminingtheFringregion,Murrayalsodetectedapreviouslyunknownring,S/20041R,associatedwithSaturn'oon,Atlas.ItisknownfromVoyagerthattheregionbetweenthemainringsandtheFringisdusty,buttheroleofthemoonsinthisregionwasamystery,"Murrayexplains."ItwaswhilestudyingtheFringintheseimagesthatthefaintringofmaterialwasdiscovered.AftersomecalculationAtlaswasidentifiedastheprimesuspect."

Withawidthestimatedat300km(190miles),theringislocated138,000km(about86,000miles)fromthecenterofSaturnintheorbitofthemoonAtlas,betweentheAringandtheFring.TheringwairstspottedinimagestakenafterCassini-HuygensorbitinsertiononJuly1,2004.Thereisnowayofknowingyetifitextendsallthewayaroundthepla.SearcheswillcontinueforfurtherdetectionsofthenewfoundbodyorbodiesseeninassociationwiththeFring.Ifthetwoobjectsindeedturnouttobeasinglemoon,itwillbringtheSaturnmooncountto34.ThenewfoundringaddstothegrowingnumberofnarrowringletsaroundSaturn.19

ToBeContinued...

IntheperiodfromDecember25th,2004,toJanuary14,2005,thescheduleddescentoftheHuygensprobethroughTitan'sthickatmospherewilltakeplace,culminatingintheactuallandingoftheprobeonTitan'ssurface.Ifallgoeswell,Titanwillbethefarthestplaarybodythatanyman-madespacecrafthaslandedonsofar.AsHuygensperatesTitan'shazyatmosphereduringitsdescentandlanding,moreandmoreofthemysteriessurroundingthiostintriguingofallthesolarsystemsatelliteswillbeunveiled.Staytuned！

来源于:小马过河

相关推荐:

托福阅读常出现的9个深度句

托福阅读利剑之语法

托福阅读解题方法之《主旨题》

全国免费咨询:400-0123-267