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Solar winds speed up and blow away remaining gas, planets stickHeavy bombardment: leftover planetesimals bombarded other objects in late stages of solar system formationoFates of planetesimals: ejection or collision, comets and asteroids are leftover planetesimalsCosmic water: water may have come to Earth by way of ice-rich planetesimals from outer solar systemMoon’s formation: giant impact theory, giant impact made the moon, moon’s mantle material from Earth and impactorSolar Nebula hypothesis: o1. Solar nebula contracts due to its own gravity (spins faster as it contracts, conserve angular momentum)o2. Protosun forms at center (nebula flattens into disk)o3. Dust grains condense out of gas; grains accrete into planetesimalso4. Large planetesimals accrete smaller ones, grow to become planetsRate of radio-active decay is measured in half-lives. Mercury, Venus, Earth (+Moon), MarsInternal Structure of Earth: crust (lighter rock, floats on mantle), mantle (dense “flowable” rock), core (iron & nickel, outer core molten, inner solid)Terrestrial basic structure: core (high density, metal, iron & nickel), mantles (dense rock surrounds core), crusts (low density rock, granite)oStructure produced by differentiation (materials separated by density)Process that shape surfaces: impact cratering, volcanism, tectonics, erosionImpact Crater Formation: 1. Contact/compression, 2. Excavation, 3. Modification, (results from collision of an extraterrestrial body with surface of planet or moon)Tectonics: any stretching or compression of a planet’s crust, due to convection currents in the mantle
Size determines a world’s level of geological activity: more volume =more internal heat; more surface area=faster heat lossCrater density can tell a surface’s age. Older = more cratersMoon’s defining feature: Impact cratersLunar regolith= moon covered with gently rolling layer of powderly soil w/ scattered rocks called…, made from debris blasted out of lunar craters by meteor impacts that created themLunar Maria= darker, smooth, low-lying plains, few craters; formed from large objects striking lunar surface, molten material from interior flooded these cratersLunar Highlands= lightly-colored hilly regions, covered in cratersMercury: barren, airless world, surface similar to moon’s, mercury is small (cooled rapidly); scarps = long cliffs, formed when core shrunk while cooling, crust wrinkledVenus: similar size to Earth, few craters, craters are “rough”; volcanoes, 80% of surface covered in lava flows, crust lacks plate tectonicsMars: broad volcanoes, windswept plains, canyons, S-Hemi heavily cratered highlands, N-hemi volcanic lowland plains; iron mineral hematite lies on surface parts, often forms in presence of liquid water (blueberries = hematite concretions); Opportunity and Spirit missionsVenus, Earth, and Mars all have atmospheres; Venus and Mars atmospheres mostly made of CO2