Download Origin of the Solar System

Origin of the Solar
System
Born with the Sun
Big Picture!
The solar system was born
from the gravitational
contraction of a large,
rotating cloud of gas and
dust some 4.6 Gy ago.
Elements of a Model
• Dynamical properties (motions)
• Chemical properties
(composition)
• Formation of planets, satellites,
and other stuff
• Evolution of planets, satellites, and
other stuff
Nebular (“Cloud”) Model
• Origin: Rotating interstellar
cloud of gas and dust
• Contraction: Self gravity brings
cloud together; becomes
denser; heats up; forms a disk
with bulge in center
Nebular Model
• Sun: Forms at center; reflects
original composition of cloud
• Planets: Form in disk by
accretion of smaller bodies;
composition determined by
local temperature
• Debris: Remnants of materials
in cloud
Angular Momentum
• Tendency for spinning/orbiting
mass to continue
spinning/orbiting
• Total angular momentum
constant for an isolated system
• Demands that as a spinning
cloud contracts, it spins faster
& forms disk with central bulge
The Bad News
• Planets have too much angular
momentum (orbital), sun too
little angular momentum (spin)
• Way out: Magnetic fields
transfer spin from central parts
of cloud to out parts while gas
in disk still a plasma (hot!)
The Good News
• Planets orbit in a plane in near
circular paths
• Planets orbit and spin in the
same direction as original spin
• Most satellites and rings orbit
and spin in same direction
Formation of Planets
• Condensation: Gas => Grains
• Accretion: Grains hit & stick,
make pebbles, hit & stick, make
planetesimals
• Gravitational attraction makes
planetesimals => protoplanets
Chemical Condensation
• Temperature in disk drops
rapidly outward from sun
• Lowest local temperatures
determines what kinds of
grains condense: metal, rocks
+ metals, ices + rocks, ices,
gases + ices, gases
Chemical Condensation
• Near sun, more metals and
rocks (terrestrial); farther out,
greater ices and gases (Jovian)
• Asteroids: Uncollected
“terrestrial” planetesimals
• Comets: Uncollected “Jovian”
planetesimals