Chapter 22 - Chapter 22 Planetary Geology Two types of...

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Chapter 22: Planetary Geology I) Two types of planets: A) Terrestrial planets (Earth-like): Mercury, Venus, Earth, Mars 1) Called the inner planets 2) Densities are 5x greater than water a) Consists mostly of rocky and metallic substances b) Minor amounts of gases and ices 3) Meager atmospheres B) Jovian planets (Jupiter-like): Jupiter, Saturn, Uranus, and Neptune 1) Much larger size and mass than terrestrial planets (often called giants) 2) Called the outer planets 3) Densities only 1.5x greater than water a) Contain large amounts of gases and ices b) Also have rocky/metallic materials in cores 4) Thick atmosphere of hydrogen, helium, methane ammonia II) Differences b/t two types A) Densities: due to composition B) Atmosphere: ability to retain atmosphere depends on its mass and temp. 1) A gas molecule can evaporate from a planet if it reaches escape velocity 2) Jovian planets have high escape velocities b/c of greater surface gravities  3) Molecular motion of gas is temperature dependent—low temperature of Jovian  planets small speeds III) Substances of planets are divided into three groups A) Gases: hydrogen and helium with melting points near absolute zero B) Rocks: silicate minerals and metallic iron—melting points that exceed 700 oc C) Ices: ammonia, methane, carbon dioxide, water with intermediate melting points IV) Earth’s moon: unusually large compared to its parent planet A) Density: 3.3x that of water 1) Moon’s iron core is small 2) Gravitational attraction is 1/6 that of Earth’s B) Two different types of terrain 1) Maria (mare): dark lowlands a) Seas of basaltic lava b) Originated when asteroids punctured lunar surface letting basaltic magma bleed out c) Craters were flooded with layers of fluid basaltic lava d) Often 30 meters thick 2) Bright cratered highlands: make up most of surface—contains mountains C) No atmosphere or water 1) Weathering and erosion does not occur 2) Tectonic forces are not active on moon 3) Unprotected by an atmosphere
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a) Tiny particles continually bombard surface b) Gradually smooth the landscape c) Moon rocks become slightly rounded on top if they are long exposed to lunar surface D) Craters: produced by impact of rapidly moving debris 1) More common in early history of solar system 2) Lack of air friction allows meteoroids to reach the ground
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