天文学英文版PPT资料 (9)

UniverseEighthEditionRogerA.Freedman•WilliamJ.KaufmannIIICHAPTER8ComparativePlanetologyIITheOriginofOurSolarSystemHW–Chapter8OnlineQuizdueMonday10/118-1Thekeycharacteristicsofthesolarsystemthatmustbeexplainedbyanytheoryofitsorigins8-2Howtheabundancesofchemicalelementsinthesolarsystemandbeyondexplainthesizesoftheplanets8-3Howwecandeterminetheageofthesolarsystembymeasuringabundancesofradioactiveelements8-4WhyscientiststhinktheSunandplanetsallformedfromacloudcalledthesolarnebula8-5Howthesolarnebulamodelexplainstheformationoftheterrestrialplanets8-6TwocompetingmodelsfortheoriginoftheJovianplanets8-7HowastronomerstestthesolarnebulamodelbyobservingplanetsaroundotherstarsByreadingthischapter,youwilllearnA.OverestimateofthetrueageB.UnderestimateofthetrueageKeyIdeasModelsofSolarSystemFormation:Themostsuccessfulmodeloftheoriginofthesolarsystemiscalledthenebularhypothesis.Accordingtothishypothesis,thesolarsystemformedfromacloudofinterstellarmaterialcalledthesolarnebula.Thisoccurred4.56billionyearsago(asdeterminedbyradioactivedating).KeyIdeasTheSolarNebulaandItsEvolution:Thechemicalcompositionofthesolarnebula,bymass,was98%hydrogenandhelium(elementsthatformedshortlyafterthebeginningoftheuniverse)and2%heavierelements(producedmuchlaterinthecentersofstars,andcastintospacewhenthestarsdied).Theheavierelementswereintheformoficeanddustparticles.KeyIdeasFormationofthePlanetsandSun:Theterrestrialplanets,theJovianplanets,andtheSunfolloweddifferentpathwaystoformation.Thefourterrestrialplanetsformedthroughtheaccretionofdustparticlesintoplanetesimals,thenintolargerprotoplanets.Inthecoreaccretionmodel,thefourJovianplanetsbeganasrockyprotoplanetarycores,similarincharactertotheterrestrialplanets.Gasthenaccretedontothesecoresinarunawayfashion.KeyIdeasInthealternativediskinstabilitymodel,theJovianplanetsformeddirectlyfromthegasesofthesolarnebula.Inthismodelthecoresformedfromplanetesimalsfallingintotheplanets.TheSunformedbygravitationalcontractionofthecenterofthenebula.Afterabout108years,temperaturesattheprotosun’scenterbecamehighenoughtoignitenuclearreactionsthatconverthydrogenintohelium,thusformingatruestar.KeyIdeasExtrasolarPlanets:Astronomershavediscoveredplanetsorbitingotherstars.Mostoftheseplanetsaredetectedbythe“wobble”ofthestarsaroundwhichtheyorbit.Asmallbutgrowingnumberofextrasolarplanetshavebeendiscoveredbythetransitmethod,bymicrolensing,anddirectimaging.Mostoftheextrasolarplanetsdiscoveredtodatearequitemassiveandhaveorbitsthatareverydifferentfromplanetsinoursolarsystem.