Lecture_6_Planet_formation

Lecture_6_Planet_formation - Universe: H, He Sun (formed...

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1 1 Universe: H, He Sun (formed from supernova remnants): H, He, C, N, O, Ne, Mg, Si, Fe Earth: O,Mg,Si,Fe Life: C,H,O,N 2 15 10 5 0 Nucleosynthesis Solar system forms Today Big Bang ? Billions of Years Ago
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2 3 Solar system picture Note: size of sun, planets and orbits not to scale 4 1. Orbital motion- same direction as sun, circular 2. Orbital spacing 3. Comets 4. Planetary rotation - 6 rotate with sun, 3 rotate other way, axis tilts <30° 5. Satellite Systems 6. Planetary masses 7. Bulk compositions 8. Asteroid belt 9. Asteroids and meteorites 10. Ages Properties of the Solar System which any theory of origin must explain:
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3 5 Solar Nebula/ Planetesimal Hypothesis • Interstellar medium will collapse to form a central star surrounded by a disk of gas, ices, and dust • Dust and ice will settle toward mid-plane of disk • Large particles will sweep up smaller ones into clumps • Clumps will grow into planetesimals and then planets, sweeping clean the disk 6 Possible molecules in a solar nebula (simplified) Gas: Ne, He, H 2 Ice: CH 4 (methane) NH 3 (ammonia) H 2 O (water) Dust: Mg 2 SiO 4 , MgFeSiO 4 (olivine) FeSiO 3 , MgSiO 3 (pyroxene) Fe (iron metal)
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4 7 Volatile compound : transitions from solid to liquid to gas occur at low temperature Refractory compound : transitions from solid to liquid to gas occur at high temperature 8 Compound Melting Point of Solid (°C) CH 4 -184 NH 4 -74 H 2 O 0 Fe 1540 SiO 2 1710 Mg 2 SiO 4 1890 Al 2 O 3 2045
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5 9 1.Solar Nebula: Rotating gas/dust/ice cloud will collapse into a star surrounded by a disk. Gas: H, He + others Ices: H 2 0 (water), CH 4 (methane), NH 3 (ammonia) + others Dust: heavier elements and compounds This disk should be compositionally similar to the star. Mass concentration and temperature in the disk should decrease outward from the star Which elements are in solid vs. gaseous form will depend on the temperature (distance from star).
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Lecture_6_Planet_formation - Universe: H, He Sun (formed...

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