AST-L9-ch6__3

AST-L9-ch6__3 - "Terrestrial Planet Interiors Today's...

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1 1) History of Terrestrial Planets Four major processes: -- differentiation, cratering, volcanism, weathering and gradation 2) Density r = M/V 3) Heat Transfer 4) Planetary Magnetism Today’s Lecture: purpose & goals AST 1002 Planets, Stars and Galaxies Terrestrial Planet Interiors “Comparative Planetology -- learn by comparing planet’s properties; Understand the concepts of: Review Pieces of the Solar System Sun (in a few weeks) inner ( terrestrial ) planets (this week) outer ( jovian ) planets (next week) other stuff (following week) Angular momentum angular momentum is conserved Solar System formation accretion disk, rotation, protostar Planetesimals, and solar wind Introduction Terrestrial Planets Small, rocky worlds Mercury Venus Earth Mars (can also include Earth’s Moon ) Comparative Planetology Helps us understand: Weather Earthquakes Climate
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2 Basic Facts about Earth Radius About 6400 km Shape Oblate spheroid Polar radius 21 km shorter Composition Mostly made of materials denser than rock. The average density is 5,520 kg/m 3 . Measuring the Earth’s Mass In order to compute the Earth’s density we need The Earth’s radius The Earth’s mass To measure the mass we need to consider Newton’s laws of motion Newton’s law of gravity m F a = 2 2 1 R m m G F = Newton’s 2 nd Law Newton’s Law of Gravity R m 2 m 1 Measuring the Earth’s Mass – II Radius of Earth is measured to be R = 6.4 x 10 6 m Newton’s constant is measured to be G = 6.7 x 10 -11 Nm 2 /kg 2 The acceleration due to gravity at Earth’s surface is measured to be a = 9.8 m/s 2 G R a M 2 = 2 R GM a = Re-arrange to get: M = 6 x 10 24 kg Density = Mass / Volume Mass of Earth M = 6 x 10 24 kg Radius of Earth R = 6.4 x 10 6 m Volume of Earth V = 4 π R 3 /3 V = 1.1 x 10 21 m 3 3 3 21 24 kg/m 500 , 5 m 10 1 . 1 kg 10 6 Density = × × =
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3 Structure of Earth Crust Solid , thickness: 35-60km; silicates (Oxygen and Silicon compounds).
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