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Chapter 9

Astronomy Chapter 9 Notes.pdf

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Astronomy 1021
Trevor Kirsh

Chapter 9: Planetary Geology • Core are the highest density material of The geology of the terrestrial primarily of nickel and iron • Mantle are rocky material of minerals worlds like silicon oxygen etc • Crus is low density rocks such as • The terrestrial worlds all looked much granite and basalt that forms a thin the same when they were born crust/outer skin • Their present day differences are a • Earth and Venus has inner and outer result of geological process that cores occurred in the ensuing 4.3 billion • Theres layers because stuff with less years density rise to the top, its called • The extent to which different geological differentiation processes operate on different worlds • Mercury has a large core because a depends largely on their fundamental giant impact blasted away its outer properties, especially their size layer • A planet’s geology is largely destined • Moon has a small core because it was from its birth, which means we should just a piece of Earth’s blasted off outer be able to predict the geology of as- layer with really little high density yet-undiscovered planets once we material inside know their fundamental properties • Lithospheres are cool rigid rocks • Earth has been affected by the same • Worlds are round while smaller objects geological processes affecting the are potato shaped because they cant other worlds. overcome the rigidity of the rocky • However erosion is far more important material while bigger worlds overcome on Earth than other terrestrial world and it because of the gravity pulling it into a Earth’s unique plate tectonics may be sphere very important to our existence • Planetary geology is the study of Earth What causes geological activity? and other worlds • Interior heat drives geological activity by causing mantle convection, keeping 9.1 the lithosphere thin and keeping the interior partially molten What are the terrestrial planets like on • 3 sources of internal heat: accretion, the inside? differentiation, radioactive decay • In order of increasing density and • Accretion is when gravitational potential depth, the interior structure consists of energy is converted into kinetic energy core, mantle, and crust into thermal energy • The crust and part of the mantle • Differential is when dense materials together make up the rigid lithosphere. sink to the core converting gravitational In general a thinner lithosphere allows • potential energy from friction and then more geological activity into thermal energy • We were able to study this with seismic • Radioactive Decay is the mass energy waves, vibrations that travel both contained in the nuclei converted into through the interior and along the thermal energy surface after an earthquake • Larger planets retain internal heat longer • The 3 ways for planets to cool off are wind water ice and weather convection conduction and radiation • Erosions form sedimentary rocks over • Convection is when hot rocks rises and time cooler rocks sink (into convection cells) so heat transfers upwards How do impact craters reveal a • Conduction is when heat is transferred surface’s geological age? from hot to cool materials through • More craters indicate an older surface. contact to the surface • All the terrestrial worlds were battered • Radiation is the transfer of heat from by impacts when they were young, so thermal radiation those that still have many impact craters must look much the same as Why do some planetary interiors they did long ago create magnetic fields? • Those with fewer impact craters must • The magnetic field protects Earths have had their ancient craters erased atmosphere from being stripped away by other geological processes into space by particles • Lunar highlands have a lot of craters • A planetary magnetic field requires • Lunar maria we see a few craters three things: an interior layer of electrically conducting fluid, convection Why do the terrestrial planets have of that fluid, and rapid rotation. different geological histories? • Among the terrestrial planets, only • Fundamental planetary properties, Earth has all three characteristics especially size, determine a planet’s geological history • Larger worlds have more volcanism 9.2 and tectonics, and these processes erase more of the world’s ancient What processes shape planetary impact craters surfaces? • Erosion depends on a planet’s size, • The four m
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