Astro 120 Fall 2008: Lecture 25 page 1
Reading: Chapter 8, Sect. 8.1-8.4, 9.6; Chapter 13
Final Exam: Tuesday, December 16; 4:30-6:30PM Physics 3, 5; Lago 142
Homework 10: Due this Friday/Monday, December 5/8!
Brief review of last time: Our Sun
•The SUN: a star, up close and personal
•vital statistics
•photosphere, chromosphere, corona
•the solar cycle
•Source of the Sun’s energy:
•combustion fails - 10,000 years of fuel
•contraction fails - 100,000,000 years of “fuel”
•Hydrogen Fusion: the p-p chain
•4 H1 ! He4 + photons + neutrinos
•0.7% of mass of H converted to energy via E=mc2
•energy source for 10 billion years
Astro 120 Fall 2008: Lecture 25 page 2
The Solar Nebula Theory
http://www.jach.hawaii.edu/JCMT/publications/newsletter/n16/fom_ann.jpg
The planets formed in a dust-filled disk of gas
surrounding the very young Sun
Astro 120 Fall 2008: Lecture 25 page 3
•Where to begin?
•Evidence from our current Solar System
•Evidence from the Stars
•First phases: collapse to star plus disk
•interstellar cloud – gravity takes over
•angular momentum –"disk formation
•The Solar Nebula
•mass and composition
•temperature distribution
•Planet formation
•condensation
•accretion into planetessimals
•accretion into planets and satellites
Formation of Planetary Systems
Astro 120 Fall 2008: Lecture 25 page 4
•Evidence from our current Solar System
•all planetary orbits are
•counterclockwise
•nearly circular
•nearly in the same plane
•inner planets are rocky
•outer planets are gas balls
•oddball exceptions (Pluto’s orbit, Uranus rotation)
•Evidence from the Stars
•there are many other solar systems
•there are many multiple star systems
•youngest stars are embedded in dust and gas
•planetary systems form quickly
Where to begin?
Planets
formed out
of a disk
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