L20GH09Planet_formation

L20GH09Planet_formation - Formation of planets Lecture...

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March 19, 2009 planet formation Formation of planets •Lecture topics: •Text reading: Chapter 5
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March 19, 2009 planet formation
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March 19, 2009 planet formation General properties of the Solar System (i.e. things to use when modeling SS formation) 1. Patterns of motion : The theory must successfully explain the orderly patterns of motion that we observe in the solar system. ¾ all planets orbit the Sun in the same direction and with nearly circular orbits in nearly the same plane ¾ the Sun and most planets rotate in the same direction that they orbit ¾ most large moons also orbit their planets in the same direction. 2. Two types of planets : Need to explain why planets fall into two main categories: the small, rocky terrestrial planets near the Sun and the large, hydrogen-rich jovian planets farther out. 3. Asteroids and comets : The theory must be able to explain the existence of huge numbers of asteroids and comets and why these small objects reside primarily in the regions we call the asteroid belt, the Kuiper belt, and the Oort cloud. 4. Exceptions to the patterns : Finally, the theory must explain all the general patterns while at the same time making allowances for the exceptions to the general rules, such as the odd axis tilt of Uranus and the existence of Earth's large Moon.
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March 19, 2009 planet formation Planetary systems form from protostellar disks
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March 19, 2009 planet formation Disk shapes We can see that many disks are thinner in the centre than the edges. Why is this? a z r gas pressure gravitation toward sun centrifugal force ( α v 2 /r) gravitation toward nebular disk
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March 19, 2009 planet formation Mass of the Solar nebula • We can estimate the minimum mass of the solar nebula, from the existing planets. ¾ Assume solar nebula composition was initially the same as the present day solar atmosphere. ¾ Need to estimate how many volatiles have been “lost” from each planet • Minimum mass of the protoplanetary disk is about 0.03 M Sun . ¾ Much of the mass may have been expelled during the T-Tauri phase of the Sun’s formation ¾ Total mass was likely something like 0.15-0.4 M Sun .
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March 19, 2009 planet formation Solar nebula Composition: • Hot gas • Dust grains : microscopic rock or ice particles • Planetesimals : small bodies from which the planets are made up. • Protoplanet : large precursor to a planet Recall: • There is a temperature gradient in the solar nebula ¾ Hotter near the centre, where the gas is denser, so gravitational potential energy is not radiated away efficiently
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March 19, 2009 planet formation Condensation Metals Rock Hydrogen compounds H and He gas Relative abundance ( by mass) 0.2% 0.4% 1.4% 98% Comments In all but hottest regions of the nebula, these will be present in solid form (mostly olivine and pyroxene) Much of C,N,O gets locked up in these compounds. Always in the gas
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This note was uploaded on 04/15/2009 for the course PHYS 275 taught by Professor Harris during the Winter '09 term at Waterloo.

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L20GH09Planet_formation - Formation of planets Lecture...

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