Exam 1 next time !!!! Bring your #2 pencils!!!. Where did the solar system come from? Nebular theory.

Exam 1 next time !!!!

Bring your #2 pencils!!!

Where did the solar system come from?

Nebular theory

Nebula: Clouds of matter in our Galaxy

The Horse-Head Nebula

TylerCreatesWorlds

( O9 )

Our Solar system: In the beginning…

Starts as a nebular cloud of dust and gasses

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

Any finite, stationary cloud would contract on its own,

eventually

Getting started

Region of higher densityRandom clump?

Compression from a shockwave?

Speeding up the contraction

Gravitational contraction begins ….

Denser region at core

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

To conserve angular momentum, the cloud must spin faster as it shrinks

cm

Example: Conservation of (Total) Angular Momentum

Why Flatten into a disk?

Cloud now has an organized NET

rotation

All parts are attracted by gravity

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!

Why Heat up?

Compressing things:

Cool hot

Compressing gasses:

Cool hot

mechanicalwork

increased temperature

‘Adiabatic compression’

Gravitational Compression:

Cool

hot

Kelvin-Helmholtz heating

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

Atacama Large Millimeter ArrayIR image of HL Tauri.

Hubble -The Near Infrared Camera and Multi-Object Spectrometer (NICMOS)

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

“Dust seed”

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

(proto) SUN Outward

HOTTER COOLER

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

Radioactive dating

Unstable isotopes ‘decay’ by various nuclear processes.

Each such isotope is characterized by a half life:

C126 Stable!

C146 Unstable! (radioactive)

ee NC 147

146

Stable!

(a neutron inside the C-14 nucleus decays to a proton)

ee pn0

The carbon-14 decay is characterized by a‘half life’ t½ = 5,730 years.

C1024 14

start 0t

The carbon-14 decay is characterized by a‘half life’ t½ = 5,730 years.

N512

C51214

14

years 730,5t

The carbon-14 decay is characterized by a‘half life’ t½ = 5,730 years.

N687

C25614

14

years 460,11t

The carbon-14 decay is characterized by a‘half life’ t½ = 5,730 years.

N896

C12814

14

years 190,17t

The carbon-14 decay is characterized by a‘half life’ t½ = 5,730 years.

N960

C6414

14

years 920,22t

The carbon-14 decay is characterized by a‘half life’ t½ = 5,730 years.

N992

C3214

14

years 650,28t

)2ln/(0

2/1 ttenn

radio-carbon dating

Air

2Nstable C12

Air

2N

cosmic ray

stable C12

N C14

e

Air

2N

2CO

cosmic ray

stable C12

N C14

Air

2N

2CO

Cor C 1412

cosmic ray

stable C12

N C14

ppt1C

C 012

14

R

Carbon dating

C and C 1412

Carbon dating

nothing

012

14

C

C R

Carbon dating

012

14

C

C RR

time passes: NC 1414

Carbon dating

RC

C

12

14

mass spectrometer

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

Age of the solar system ?

Oldest rocks on earth: ~4 × 109 years

moon rocks: 4.4 × 109 years

meteorites: 4.55 × 109 years

(accretion period was fast ~ 0.05 × 109 years )