Transcript SSFormation2 - courses.psu.edu

Structure
&
Formation
of the
Solar System
SUN
INVENTORY
Mass Fraction
One Star (“Sun”)
99.85%
Nine (?) Planets
0.135%
80 (?) Satellites (“Moons”)
1 million (?) Asteroids
1011 (?) Comets
Meteoroids + Dust + Gas
SUN
SUN
Sun
865,000 mi
(1.39 x 106 km)
·
SUN
PLANETS
p. 122
*
*
*
*
Orbits almost in same plane
Orbit sense same
Orbits nearly circular
Rotation sense same (almost!)
* Composition gradient
Solid: Metallic,
rocky:
high density
(3.9 – 5.5 g/cm3)
Fluid: Hydrogen
& Helium:
Low density
(0.7 – 1.6 g/cm3)
SUN
MOONS
Most (mainly) orbit in same sense as planets
* Inner moons rocky; outer moons (mainly) icy!
SUN
ASTEROIDS
Main Asteroid Belt
Rocky Chunks
Some asteroids are found elsewhere . . .
Earth
Asteroid
Near-Earth Asteroids
SUN
COMETS
Kuiper Belt
Icy Chunks
Oort Cloud
100,000 AU
* Orbits in every
possible plane!
SUN
SOLAR SYSTEM FORMATION:
NEBULAR THEORY
Star Formation
Collapsing ‘Solar Nebula”
Collapse of an Interstellar Cloud
p. 127
Cloud contracts & heats
Gravitational potential
energy
Heat (thermal) energy
. . . And spins faster & flattens as it contracts
Small diameter,
rapid spin
Large diameter, slow spin
Slow
Fast
‘Difficult’ collapse
‘Easy’ collapse
~ 200 AU
Protosun
Protoplanetary Disk
. . . Leading to arrangement of planet’s orbits.
‘Circumstellar’ disks in
Orion
Disk
surrounding
star
Beta Pictoris
600 AU
SUN
MAKING PLANETS
98% H & He
Gas begins to condense to solid particles . . .
p. 128
Temp. in the Solar Nebula
Only rocky & metallic
materials solidify.
Ices can form
(in large amounts)
Distance from Sun (AU)
Cosmic Abundance of the Elements
Abundance
icy stuff
Atomic Number
Planetesimals
. . . Eventually gravity aids assembly.
Particles begin to accrete into larger chunks . . .
Small planetesimals (asteroid-like)
Large planetesimals
(planet-like)
Inner (terrestrial) planets small:
little rocky/metallic material
available
‘Nebular Capture’
Outer (Jovian) Planets: Large icy core planetesimals
gathered-in abundant H & He  Big planets!
p. 130
SUN
THE LEFTOVERS
Asteroids form here
Comets form here
Small bodies that get too close to
big planets may get ejected to far
reaches of solar system.
Many leftover
planetesimals
collided with
the planets.
p. 132
Craters, craters everywhere . . .
Mercury
Mars
Moon
Callisto (a moon of Jupiter)
Bombardment
History
Comets/Asteroids
probably delivered
most water!