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Origin of the Solar System
Astronomy 311
Professor Lee Carkner
Lecture 8
Quiz 1 Monday
Covers lectures 1-8 and associated readings
About half multiple choice (~20 questions),
half short answer/problems (~4 questions)
Study:
Notes
Can you write a paragraph explaining each major
concept?
Exercises
Can you solve all the exercises with no resources?
Readings
Can you do all the homework with no book and
Quizdom questions with no notes?
Bring pencil and calculator!
No sharing!
The Solar System
Questions

When did it form?

Why does it have structure?
Structure of the Solar System
The solar system has three distinct regions

Mercury, Venus, Earth, Mars, Asteroids
Made of metal and rock
Outer region
Jupiter, Saturn, Uranus, Neptune and Moons
Made of ice and gas

Kuiper Belt and Oort Cloud
Made of ice
Where Did the Solar System
Come From?

We can’t look back in time to see how
the Sun and planets formed, but we can
look at young stars that are forming
today
Star Formation

Due to an external stimulus (e.g.,
supernova shockwave, stellar wind)

Gravity causes the core to contract to a star
Conservation of angular momentum
makes the clump spin faster
Rapid rotation causes the outer layers to form a
disk
Circumstellar Disks
Disks are fairly cool and can be
detected with infrared and millimeter
telescopes

Disks are common around young stars
From Disks to Planets

Where does the disk go?
Formed into planets

Disks you can see, planets you can’t
How Do Planets Form?
There are 4 stages to planet formation
1
2  grains stick together to form
planetesimals
3
4  gas and leftover planetesimals are
cleared from solar system
What Was the Solar Nebula
Made of?
Solar Nebula -From studying meteorites and star
forming regions we hope to discover
what the solar nebula was made of
Two basic components
Gas -Dust -- made of rock (silicates), metal
(iron) and ices (water, methane, ammonia,
carbon dioxide)
Solar System Dust Grain
Accretion of Grains

Grains get larger by sticking together and settle
to the center of the disk

Eventually the grains form into larger bodies (a
few km in size) called planetesimals
At the end of this stage the solar system is
populated by a few thousand planetesimals, such a
system is invisible to telescopes
Disk
Star
High Density
Low
Density
Larger Grains
move to center
Accretion in a Protoplanetary
Disk
Temperature and the Solar
Nebula
Two basic types of dust in solar nebula:
Volatiles -Refractory Material --
Temperatures were higher in the inner solar
system and lower in the outer solar system

Inner solar system -- rocky planetesimals
Outer solar system -- icy planetesimals
Rocky
Icy
Gas
Temperature
Regions of Formation
Planetesimals to Planets
Due to gravity and intersecting orbits
the planetesimals collide with each
other

Planet formation happens differently in
inner and outer solar system
Formation of Gas Giants
In the outer solar system you have more
material (both volatiles and refractory
material), so planets are larger

No more hydrogen gas after a few million years
Thus, in the outer system where the
temperatures are lower you have gas giants
Formation of Terrestrial
Planets

Result is small rocky planets with no
large gassy outer layers
Accretion of the Inner Planets
Orbital Evolution

This causes:
Shifting of the orbits of the Gas Giants

Icy planetesimals ejected to form the
Kuiper Belt and Oort cloud
The Final Solar System
Our picture of planet formation is driven
by an attempt to explain our own solar
system and its three regions

Outer or Gas Giant region
Trans-Neptunian or Cometary Region
We have also found other types of
planetary systems different from our own

Steps in Solar System Formation
1 Inner solar system -- volatiles boil off,
resulting in small rocky planets
2 Outer solar system -- large planet cores
form rapidly from refractory and icy
material, acquire large gas envelopes
3 Edge of solar system -- leftover and
ejected icy planetesimals form Kuiper
belt and Oort cloud