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What’s it made of?
Hydrogen 71%
Helium 27%
“Others” 2%
all the other elements
98%
Where did it come from?
Big BangOUR thin cloud of
dust and gasses
H and He
H and HeGenerations of stars are
born and die, enriching the interstellar medium with
“metals”
Stellar Fusion:H, He → “others”
“2% others”H and He
≈ 14 billion years ago
Galactic recycling
≈ 5 billion years ago
Getting started
Region of higher densityRandom clump?
Compression from a shockwave?
Speeding up the contraction
As the Nebula condenses ….
• It Spins faster• It flattens• It heats up
Random motions become more organized as the density increases and ‘clumps’ merge
Why Spin Faster?
Once the motions become more organized there must be some net angular momentum about the cloud’s center on mass …
cm
All parts are attracted by gravity
Centripetal force is greater, the farther away from the spin
axis!
All parts are attracted by gravity
Centripetal force is greater, the farther away from the spin
axis!
The Net force is greatest at the poles
All parts are attracted by gravity
Centripetal force is greater, the farther away from the spin
axis!
Gravitational Compression:
Cool
hot
Kelvin-Helmholtz heating
gravitationalwork
increased temperature
Velocity increases!
Temperature distribution in the disk is uneven
proto-sun
inner disk outer diskproto-planetary disk
orbits ‘stabilize’
Temperature distribution in the disk is uneven
proto-sun
inner disk outer diskproto-planetary disk
Low pressure-COOLContraction slows
Higher pressure-HOTContraction continues
Condensation Temperature:
For a given (low) pressure, a gaseous substance has a Condensation temperature:
If T > Tc then it remains gaseous
If T < Tc then it starts to condense into …
snowflakes
dust/seed particles
Temperature distribution in the disk is uneven
proto-sun still contracting …
pressure and temp. still increasing
metals, rocks Ices, metals, and rocks
gas
Frost line
Inside the frost line
GAS: H, He, others (2%)
(proto) SUN Outward
HOTTER COOLER
Metallic seeds condense 0.2%
Mineral seeds condense 0.4%
( Carbon-rich minerals )
TOO
HO
T
Accretion
seeds
electrostatic
GAS: H, He, othersproto-planets
Near-orbit accretion ( low DV )soft collisions
Accretion
seeds
electrostatic
clumps
gravity
GAS: H, He, others
Near-orbit accretion ( low DV )soft collisions
Accretion
seeds
electrostatic
clumps
gravity
GAS: H, He, othersplanetesimals
Near-orbit accretion ( low DV )soft collisions
Accretion
seeds
electrostatic
clumps
gravity
GAS: H, He, othersplanetesimals proto-planets
Near-orbit accretion ( low DV )soft collisions
The battle of the proto-planets
Bullying by the big
mess up the orbits of the smallshatter them or …
eat them…
Winners: PlanetsLosers: Asteroids
Beyond the frost line
Now H-compounds can condense to form ices:e.g. H2O, NH3, CH4
Recall the make-up of our solar nebula:
• H and He (98%) Never condense at these pressures
• H-compound “ICES” (1.4%)
• Rock and metals (0.6%)
3× the solids available in the terrestrial zone
Beyond the frost line
GAS: H, He
Accretion here now leads to bigger proto-planets made of rock and ices
Beyond the frost line
GAS: H, He
Accretion here now leads to bigger proto-planets made of rock and ices
proto-planets massive enough to capture H and He gasses … so mass increases more
Beyond the frost line
GAS: H, He
Accretion here now leads to bigger proto-planets made of rock and ices
proto-planets massive enough to capture H and He gasses … so mass increases more
Process continues until local gas is bound up into a “Gas Giant”
The young Jovian planets would follow the same scenario as the evolving solar nebula:
Accretion disk evolves into lots of planets!
Meanwhile …. Back at the center
hot hotter ignition stabilized
proto-sun
heat source: gravitational energy
sun
heat source: fusion energy
Heavy mass ejection ….
ignition stabilized
Massive* solar winds are ejected…
These sweep away the H and He gas of the nebula …
* These solar winds can be 106 to 107 × present rates
Unstable isotopes ‘decay’ by various nuclear processes.
Each such isotope is characterized by a half life:
C126 Stable!
C146 Unstable! (radioactive)
Carbon dating
012
14
C
C RR mass spectrometer
)2ln/(0
2/1 tteRR
now
12
14
C
C
standard
12
14
C
C
years ,7505