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Week 3- Part 13:Planets orbit Sun in same direction and in nearly the same plane Two main planet types: Terrestrial and JovianSmaller bodies: Dwarf planets, asteroids, comets, moonsThe definition of a planetis in orbit around the Sunhas sufficient mass so that it assumes a nearly round shape has cleared the neighborhood around its orbitDwarf planets satisfy the first two, but not the thirdPart 14:What properties of solar system must a formation theory explain?Motions of large bodies; 2 types of planets; Asteroids and cometsWhat theory best explains the features of our solar system?Nebular theory states that solar system formed from a large interstellar gas cloud. What caused the orderly patterns of motion in our solar system?Solar nebula spun faster as it contracted, flattened into a diskWe have observed such disks around newly forming starsThe solar nebula hypothesis: in a nutshell1. Solar nebula contracts due to its own gravitySpins faster as it contracts -conserve angular momentum2.Protosun forms at centerNebula flattens into a disk3.Dust grains condense out of gas; grains accrete into planetesimals4.Large planetesimals accrete smaller ones, grow to become planets Why are there two types of planets?Only rock and metals condensed inside the frost lineRock, metals, and ices condensed outside the frost linePlanetesimals then accreted into planetsIce particles outside frost line made outer planets more massiveGravity of these massive planets drew in H, He gasesWhere did asteroids and comets come from?They are leftover planetesimals, according to the nebular theoryWhen did the planets form?Radiometric dating indicates planets formed 4.6 billion yaPart 15:What are terrestrial planets like on the inside?Core, mantle, crust structure; Denser material deeper insideWhat processes shape planetary surfaces?Cratering, volcanism, tectonics, erosionWhat determines a world’s level of geological activity? Interior heat drives geological activityBig planets cool off slower than small ones Radioactive decay is currently main heat sourceAmount of cratering tells us how old the surface isPart 16:What geological processes shaped our Moon?Early cratering still present; Maria resulted from volcanismWhat geological processes shaped Mercury?Cratering and volcanism similar to MoonTectonic features indicate early shrinkageWhat are the major geological features of Venus?Venus has few craters - young surface (Dominated by volcanism)Also has tectonics but little or no erosionWhat are the major geological features of Mars? Differences in cratering across surface; Giant shield volcanoesEvidence of tectonic activityWhat geological evidence tells us that water once flowed on Mars?Features that look like dry riverbeds; Some craters appear erodedRovers have found rocks that appear to have formed in waterPart 17:Which terrestrial planets have significant atmospheres?Venus, Earth, and Mars have significant atmospheresWhat features of