天文学英文版PPT资料 (14)

UniverseEighthEditionRogerA.Freedman•WilliamJ.KaufmannIIICHAPTER14Uranus,Neptune,Pluto,andtheKuiperBeltOnlineQuizfromChapter11dueWednesday10/20OnlineQuizfromChapter12,13,14dueMonday10/25(relax,Ch.14isprettyshort).SkipChapter15(“VagabondsoftheSolarSystem”)ExamIInowonWednesday10/27(Ch.7-14).HalfofthelectureperiodMonday10/25willbedevotedtocomprehensivereviewlikelasttime.HWandExamIIKeyIdeasDiscoveryoftheOuterPlanets:Uranuswasdiscoveredbychance,whileNeptunewasdiscoveredatalocationpredictedbyapplyingNewtonianmechanics.Plutowasdiscoveredafteralongsearch.AtmospheresofUranusandNeptune:BothUranusandNeptunehaveatmospherescomposedprimarilyofhydrogen,helium,andasmallpercentageofmethane.Methaneabsorbsredlight,givingUranusandNeptunetheirgreenish-bluecolor.NowhiteammoniacloudsareseenonUranusorNeptune.Presumablythelowtemperatureshavecausedalmostalltheammoniatoprecipitateintotheinteriorsoftheplanets.Alloftheseplanets’cloudsarecomposedofmethane.KeyIdeasMuchmorecloudactivityisseenonNeptunethanonUranus.ThisisbecauseUranuslacksasubstantialinternalheatsource.InteriorsandMagneticFieldsofUranusandNeptune:BothUranusandNeptunemayhavearockycoresurroundedbyamantleofwaterandammonia.Electriccurrentsinthesemantlesmaygeneratethemagneticfieldsoftheplanets.ThemagneticaxesofbothUranusandNeptunearesteeplyinclinedfromtheiraxesofrotation.Themagneticandrotationalaxesofalltheotherplanetsaremorenearlyparallel.ThemagneticfieldsofUranusandNeptunearealsooffsetfromthecentersoftheplanets.KeyIdeasUranus’sUnusualRotation:Uranus’saxisofrotationliesnearlyintheplaneofitsorbit,producinggreatlyexaggeratedseasonalchangesontheplanet.Thisunusualorientationmaybetheresultofacollisionwithaplanet-likeobjectearlyinthehistoryofoursolarsystem.SuchacollisioncouldhaveknockedUranusonitsside.RingSystemsofUranusandNeptune:UranusandNeptunearebothsurroundedbysystemsofthin,darkrings.Thelowreflectivityoftheringparticlesmaybeduetoradiation-darkenedmethaneice.KeyIdeasSatellitesofUranusandNeptune:Uranushasfivesatellitessimilartothemoderate-sizedmoonsofSaturn,plusatleast22moresmallsatellites.Neptunehas13satellites,oneofwhich(Triton)iscomparableinsizetoourMoonortheGalileansatellitesofJupiter.Tritonhasayoung,icysurfaceindicativeoftectonicactivity.TheenergyforthisactivitymayhavebeenprovidedbytidalheatingthatoccurredwhenTritonwascapturedbyNeptune’sgravityintoaretrogradeorbit.Tritonhasatenuousnitrogenatmosphere.KeyIdeasWorldsBeyondNeptune:Plutoanditsmoon,Charon,movetogetherinahighlyellipticalorbitsteeplyinclinedtotheplaneoftheecliptic.MorethanathousandicyworldshavebeendiscoveredbeyondNeptune.PlutoandCharonarepartofthispopulation.Mosttrans-NeptunianobjectslieinabandcalledtheKuiperbeltthatextendsfrom30to50AUfromtheSun.Neptune’sgravityshapestheorbitsofobjectswithintheKuiperbelt.