14. SS Formation Student

7/23/2019 14. SS Formation Student

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Welcome to the Solar System



The Birth of the Solar System

• Our goals for learning

• Where did the solar system come from?

• What caused the orderly patterns of motion

in our solar system?



What properties of our solar system

must a formation theory explain?

1. Patterns of motion of the large bodies – Orbit in same direction and plane

2. Existence of different types of planets – rocky close to Sun, gaseous/icy far from Sun

3. Existence of smaller bodies – Asteroids and comets



A formation theory must conform to our

knowledge of physics and chemistry

From previous section:

• Conservation of mass• Conservation of angular momentum

• Conservation of energy

– (converts between potential, kinetic andradiative)



A formation theory must include

evidence from formation of other stars

We can see stars

forming in

interstellar gasclouds

The gas clouds form

from the remains of

older stars

http://orion_nebula_proplyds.htm/



•

• Often we see disks of gas and dust aroundnew stars

• In one case a new planetary object is forming

inside the dust disk

Disks around Other Stars



What theory best explains the

features of our solar system?• The nebular theory states that our solar system formedfrom the gravitational collapse of a giant interstellar gascloud—the solar nebula

• (Nebula is the Latin word for cloud)

• A large amount of evidence now supports this idea

• Three stage process:-

1. Cloud collapse2. Condensation and planet formation

3. Final sweep-up



Conservation of

Angular Momentum

• Any pre-existingrotation of the

cloud from whichour solar systemformed, must havespeeded up as the

cloud contracted



Rotation of a

contractingcloud speeds

up for the

same reason a

skater speeds

up as she pulls

in her arms



• Collisions between particles in the

cloud caused it toflatten into a disk

Flattening



Collisions

between gas particles in

cloud

gradually

reduce random

motions



Collisions

between gas particles also

reduce up

and down

motions



Spinningcloud

flattens as it

shrinks



What have we learned?• Where did the solar system come from?

– stellar recycling built the material from which planetsformed.

– We can observe stars forming in other gas clouds.

• What caused the orderly patterns of motion in

our solar system? – Solar nebula spun faster as it contracted because of

conservation of angular momentum

– Collisions between gas particles then caused the

nebula to flatten into a disk – We have observed such disks around newly forming

stars



The Formation of Planets


• Why are there two main types of planets?

• How did terrestrial planets form?

• How did jovian planets form?



Why are there two main types of planet?



As gravity

causes cloud

to contract, itheats up

Conservation

of Energy



Inner parts of disk are hotter than outer parts.

Only materials that solidify at high temperatures can condense to

solid particles.

Rock and iron can be solid at much higher temperatures than ice,

so it becomes solid particles in the inner disk, while ice can't.



Inside the frost line: Too hot for hydrogen compounds to form ices.

Outside the frost line: Cold enough for ices to form.



How did the planets form?

• Small particles of material were presentand began to collide

• Planetesimals built up as these particlescollided and stuck together (accretion)

• Gravity eventually assembled these

planetesimals into planets



Tiny solid particles

stick to form planetesimals.

Gravity draws

planetesimals

together to form

planets

This process ofassembly

is called accretion



Accretion of Planetesimals

• Many smaller objects collected into just afew large ones



How did the types of planet form?

• Inside the frost line, the particles were of rockand metal only. Making rocky planetesimalsthen rocky planets

• Outside the frost line, the small particles weremostly ice.

• Larger planetesimals and planets were able to

form.• Gravity of these larger planets was able to draw

in surrounding H and He gases.



Moons of jovian planets form in miniature disks



© 2014 Pearson Education, Inc.

Where are hydrogen compounds

(volatiles) found in solid forminside the solar system?

A)between the rock/metal condensation line and the frost line only

B) outside the frost line only

C) everywhere outside the rock/metal condensation line

D)nowhere in the solar system

PLAY Condensates in Different Regions of the Disk

http://if_08_05_condensateregion.htm/





Where are hydrogen and helium

found in solid form inside the solarsystem?

A)between the rock/metal condensation line and the frost line only

B) outside the frost line only

C) everywhere outside the rock/metal condensation line

D)nowhere in the solar system

PLAY Condensates in Different Regions of the Disk






What happens to the number of particles as time goes on?

A)They increase.

B)They decrease.

C)They stay the same.

PLAY Accretion and the Formation of Planets

http://accretionandplanets.htm/

http://accretionandplanets.htm/



What have we learned?• Why are there two types of planets?

– Only rock and metals condensed inside the frost line – Rock, metals, and ices condensed outside the frost line

•How did the terrestrial planets form? – Rock and metals collected into planetsimals

– Planetesimals then accreted into planets

• How did the jovian planets form? – Additional ice particles outside frost line made planets there

more massive

– Gravity of these massive planets drew in H, He gases



The Aftermath of Planet Formation

- Final Sweep-up• Our goals for learning

• What ended the era of planet formation?

• Where did asteroids and comets come from?

• What happened to the rest of the planetesimals?



Outflowing

matter from

the Sun -- the

solar wind --

blew away

the leftover

gases

What ended the era of planet formation?



Where did asteroids and comets

come from?



Asteroids and Comets

• Leftovers from the accretion process

• Rocky asteroids inside frost line• Icy comets outside frost line



Heavy Bombardment

• Leftover

planetesimals

bombarded

other objectsin the late

stages of solar

systemformation



Origin of Earth’s Water

• Water may

have come to

Earth by way

of icy planetesimals

from outer

solar system



What have we learned?• What ended the era of planet formation?

– Solar wind blew away remaining gases – Magnetic fields in early solar wind helped reduce Sun’s

rotation rate

• Where did asteroids and comets come from?

– They are leftover planetesimals that never formed largerworlds

• What happened to the rest of the planetesimals?

– Most planetesimals that didn't already form large worlds,rained out causing giant impacts -called Heavy Bombardment

– This may explain some of the oddities in the solar system likeUranus orbiting on it side, or Venus rotating backwards



The Age of the Solar System


• How does radioactivity reveal an object’s

age?

• When did the planets form?



How does radioactivity reveal an

object’s age?



Radioactive Decay

• A half-life is the timefor half the nuclei in a

substance to decay

• Compare the ratio of

remaining nuclei to

decay products to date

the age of meteorites



When did the planets form?

• Radiometric dating tells us that oldest moonrocks are 4.4 billion years old

• Oldest meteorites are 4.55 billion years old• Planets probably formed 4.5 billion years ago



What have we learned?

• How does radioactivity reveal an object’s age? – Some isotopes decay with a well-known half-life

– Comparing the proportions of those isotopes with

their decay products tells us age of object• When did the planets form?

– Radiometric dating indicates that planets formed 4.5 billion years ago

14. SS Formation Student

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