DepartmentAstronomy & Astrophysics
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Chapter 8: Formation of the Solar System
8.1: The Search for Origins
−Four Criteria For Success of Solar System Formation Theory: (1) Must explain
patterns of motions discussed in chap 7. (2) Must explain why planets fall into
terrestrial(small, rocky, near Sun) and jovian(large, hydrogen-rich) categories. (3) Must
explain existence of huge numbers of asteroids + comets + why they reside in asteroid
belt, Kuiper Belt, and Oort Cloud. (4) Must explain gen. pats while allowing exceptions
AKA: Uranus Tilt + Earth’s large moon.
−Nebular Hypothesis: Prop’d by Kant + Laplace SS formed from grav collapse of
interstellar cloud of gas.
−Other prop was close encounter hypo Sun + other star collided Failed b/c (1)
Couldn’t account 4 orbtial motions of planets or division of planets into two major
categories (2) Collision btw. Sun and star significantly improbable – Stars separated too
far. Chance of encounter so small that would be difficult to imagine happening once to
form SS and doesn’t account for other planetary systems observed.
−Nebular hypothesis became Nebular Theory Successfully predicts success of other
8.2: The Birth of the Solar System
−Idea of Solar Nebula: Cloud of gas that collapsed under its own gravity to form our SS.
−Gas that made of SN contained apprx 98% H and He + 2% of all other elements.
−Three Processes of SN Alteration: (1) Heating: Temp of SN increased as collapsed
Grav pot energy conv 2 kin energy of indiv gas particles falling inward These partcls
crashed into each other, convs kin energy of inw fall 2 random motions of term energy.
Sun formed in centre where temps + densities highest. (2) Spinning: SN rotated faster
and faster till shrank in radius Rapid rot helped ensure not all materials in SN
collapsed into centre: Greater ang momentum of rot cloud, more spread out will be. (3)
Flattening: SN flattened into disk. Cons o’ collisions btw. particles in spinning cloud.
Diff clumps o’ fas within cloud move in random dircts at random speeds. – clumps
colliede + marge as cloud collapses, + each new clump has avg vel o’ clumps that formed
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