Comet Shoemaker-Levy
Bit of Administration ….
• Reading
– BSNV Chaps. 9 and 15
• Additional observations for Lab 2, through April 5
– Due April 7 in lecture or April 9 at Mathieu office
• 12-week exam in two weeks - April 12, 7:15 pm, 3425 Sterling
– Review session, Sunday, April 11, 7:30 pm, 3425 Sterling
NOTE CHANGE
IN TIME!
The Formation of the Solar System
• Dense Molecular Cores
(“Bok Globules”)
• ≈ 1 Mo
• ≈ 50,000 AU
• ≈ 10 oK
The Formation of the Solar System
The Formation of the Solar System
• Grain Collisions ==> Planetesimals (100 km)
random
100 km
The Formation of the Solar System
• Planetesimal Accretion ==> Rocky Planets and Jovian Cores
gravity
The Formation of the Solar System
• Gas Accumulation ==> H and He onto Jovian Cores
gravity
Protomoons
The Formation of the Solar System
The Formation of the Solar System
• Dispersal of Hydrogen and Helium Gas
• Solar Wind?
• Jets?
ConcepTest!
Most comets have orbits that take them well beyond Jupiter. You
would expect their composition to be:
A) Rocks and heavy elements only
B) Rocks and ices only
C) Rocks, ices, and hydrogen and helium
The Sun
QuickTime™ and a YUV420 codec dec ompres sor are needed to see this pic ture.
The Sun
The Sun is the source of (almost) all energy
in the Solar System
How does it work?
The Sun
I. Hydrostatic Equilibrium - “on average, nothing moves”
• Gravity always acts to collapse the Sun
• Gas pressure acts against collapse
Pressure
P=nkT
Number
Density
(Particles
per cm3)
Gravity
Fg =
GM1M 2
R2
Temperature
( oK )
Boltzmann
constant
The Sun
I. Hydrostatic Equilibrium
• Higher central pressure is required to hold up greater weight
Pressure
P=nkT
Gravity
Fg =
GM1M 2
R2
Central Temp = 15 million oK
Central Density = 150 gm/cm3
The Sun
High Temperatures at Center of Sun
have nothing to do with
Nuclear Energy!
Required Pressure Support
against Gravity produces
High Temperatures at Center of Sun
ConcepTest!
The atmosphere of the Earth is in hydrostatic equilibrium. This
explains why
A) Air gets colder as you climb mountains.
B) Air gets “thinner” as you climb mountains.
C) Both A and B
The Sun
II. Energy Flow
Hot
“Cool”
Temperature oK
107
0
0
Radius
1 Ro
The Sun
The Sun does NOT Shine
because of
Nuclear Energy!
The Sun Shines
because it is
Hotter in Center
than Surface
The Sun
II. Energy Flow - Mechanisms
QuickTime™ and a YUV420 codec dec ompres sor are needed to see this pic ture.
The Sun
II. Energy Equilibrium - “Energy emitted = Energy produced”
What are energy sources for Sun’s luminosity?
1. Gravity
a) Energy emitted at surface
b) Core cools down
c) Central pressure goes down
d) Sun contracts
e) Core heats up
f) Central pressure goes up
g) Energy emitted at surface ……
Energy emitted at surface <==> Star contracts
The Sun
II. Energy Equilibrium - “Energy lost = Energy produced”
What are energy sources for Sun’s luminosity?
1. Gravity
Net Effect = Energy emitted at surface and star contracts
Kelvin-Helmholtz Timescale = Time for Sun => R = 0
= 10 million years
But Earth is 4.5 billion years old,
So must be another source of energy ….
The Sun
II. Energy Equilibrium - “Energy lost = Energy produced”
What are energy sources for Sun’s luminosity?
1. Gravity
2. Nuclear
E=
Energy
(joules)
2
MC
Mass
(kg)
Speed of light
(3 x 108 m/sec)
The Sun
Thermonuclear Hydrogen Fusion
4 H => He
4 H = 4 x 1.673 x 10-27 kg = 6.693 x 10-27 kg
- 1 He
= 6.645 x 10-27 kg
_________________________________________
0.048 x 10-27 kg
(0.048 x 10-27 kg) * (3 x 108 m/s)2 = 4.3 x 10-12 joules
6 x 1014 kg H => He per second in the Sun!
The Sun
Thermonuclear Hydrogen Fusion
4 H => He
Why “Thermonuclear”?
Bringing two positive charges together
Requires high velocity = high temperature
Hydrogen
Deuterium
Positron
Neutrino
Helium 3
Helium 4
Closing Thought
•
The Second Law of Thermodynamics
Heat can never pass spontaneously from a colder
to a hotter body.
As a result of this fact,
naturalprocesses that involve energy transfer
must have one direction,
and all natural processes are
irreversible.