Comet Shoemaker-Levy

Bit of Administration …. ReadingReading –BSNV Chaps. 9 and 15 Additional observations for Lab 2, through April 5Additional 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 Sterling12-week exam in two weeks - April 12, 7:15 pm, 3425 Sterling –Review session, Sunday, April 11, 7:30 pm, 3425 Sterling NOTE CHANGE NOTE CHANGE IN TIME! IN TIME!

The Formation of the Solar System Dense Molecular Cores Dense Molecular Cores (“Bok Globules”) (“Bok Globules”) ≈ 1 M o ≈ 1 M o ≈ 50,000 AU ≈ 50,000 AU ≈ 10 o K ≈ 10 o K

The Formation of the Solar System

Grain Collisions ==> Planetesimals (100 km) Grain Collisions ==> Planetesimals (100 km) random random 100 km

The Formation of the Solar System Planetesimal Accretion ==> Rocky Planets and Jovian Cores Planetesimal Accretion ==> Rocky Planets and Jovian Cores gravity gravity

The Formation of the Solar System Gas Accumulation ==> H and He onto Jovian Cores Gas Accumulation ==> H and He onto Jovian Cores gravity gravity Protomoons

The Formation of the Solar System

Dispersal of Hydrogen and Helium Gas Dispersal of Hydrogen and Helium Gas Solar Wind? Solar Wind? Jets? Jets?

Most comets have orbits that take them well beyond Jupiter. You would expect their composition to be: A) Rocks and heavy elements only A) Rocks and heavy elements only B) Rocks and ices only B) Rocks and ices only C) Rocks, ices, and hydrogen and helium C) Rocks, ices, and hydrogen and helium ConcepTest!

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 Gravity always acts to collapse the Sun Gas pressure acts against collapse Gas pressure acts against collapse Gravity Pressure P = n k T NumberDensity(Particles per cm 3 ) Temperature ( o K ) Boltzmannconstant

The Sun I. Hydrostatic Equilibrium Higher central pressure is required to hold up greater weight Higher central pressure is required to hold up greater weight Gravity Pressure P = n k T Central Temp = 15 million o K Central Temp = 15 million o K Central Density = 150 gm/cm 3

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

The atmosphere of the Earth is in hydrostatic equilibrium. This explains why A) Air gets colder as you climb mountains. A) Air gets colder as you climb mountains. B) Air gets “thinner” as you climb mountains. B) Air gets “thinner” as you climb mountains. C) Both A and B C) Both A and B ConcepTest!

The Sun II. Energy Flow Radius 0 1 R o Temperature o K Energy flow Hot “Cool”

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

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 = 10 million years But Earth is 4.5 billion years old, But Earth is 4.5 billion years old, So must be another source of energy …. 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 = MC 2 Energy(joules) Mass(kg) Speed of light (3 x 10 8 m/sec)

The Sun Thermonuclear Hydrogen Fusion 4 H => He 4 H = 4 x x kg = x kg 4 H = 4 x x kg = x kg - 1 He = x kg _________________________________________ x kg x kg (0.048 x kg) * (3 x 10 8 m/s) 2 = 4.3 x joules 6 x 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 Positron Neutrino Deuterium Hydrogen Helium 4 Helium 3

Closing Thought The Second Law of ThermodynamicsThe 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.