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Introductory Astronomy 9精选.ppt


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Introductory Astronomy 9精选.ppt
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*ets&ObjectsBeyondNeptuneR.S.RubinsFall,2010*Asteroids1Asteroidsarerockyobjects(esimals)orbitingtheSun,typicallyoverabout100metersacross.s,whichwereformedabout4.6billionyearsagoatthesametimeastheSun.*Asteroids2Thereareprobablybillionsofasteroidslessthan1km(1000m)across,millionslargerthan1km,withabout200largerthan100km(60miles)across.ThemainasteroidbeltliesbetweenMarsandJupiter,at2.2AUand3.3AUfromtheSun.AsteroidshavedistinctlyellipticalorbitsabouttheSun,s,andinclinedtotheeclipticbyasmuchas30o.Asof2005,morethan3300asteroids,withorbitsintersectingtheEarth’sorbit,havebeenfound.Together,ofdiameterofabouthalfthatoftheMoon.Withintheasteroidbelt,theaveragedistancebetweenasteroidsisabouttenmillionkm,sothatthepossibilityofacollisionwithapassingspacecraftisnegligible.*AsteroidOrbits*s,whichwereformedwiththeSunabout4.6billionyearsago.wasformedintheasteroidbeltbecauseofJupiter’simmensegravity,whichalsocreatedgapsintheasteroidbelt,andforcedtheTrojanasteroidstoorbitintwoclustersinroughlythesameorbitasJupiter.Thelargestasteroid,Ceres,,isalmostspherical,withadiameterof930km(580miles),makingitalittlesmallerthanPluto’ssatellite,Charon.Smallerasteroids,PallasandVesta,havediametersofroughly600kmand530km(330miles)respectively.*TheAsteroidBeltTheTrojanasteroidslieintherange5.0to5.5AU,levelwithJupiter’sorbitalpath.*DawnAsteroidMission2007-20151TheDawnasteroidmissionwaslaunchedinJuly2007,andisscheduledtouseMarsforaslingshotin2009,toreachtheasteroidVestain2011,Ceresin2015.Vesta,the4thlargestasteroid,washotandvolcanicearlyinitslife,sothatitsoriginalsurfacehasprobablybeenreplacedbyancientlavaflowstogiveitasmoothsurface.Vesta’ssurfaceisdominatedbyagiantcrateratitssouthpole,about285milesacrossand8milesdeep.Ceresisthemoreinterestingobjectofstudy,sinceitisshouldbeclosetoitsoriginalstateof4.6billionyearsago.Ceresisthoughttocontainalayerofwaterice(andpossiblyliquidwater)40to80milesthick,whichhaskeptitssurfacecool,andeliminatedvolcanicactivity.*DawnAsteroidMission2007-20152Unlikethechemicalrocketsofp 内容来自淘豆网www.taodocs.com转载请标明出处.