How did the Solar System
form?
Is our solar system unique?
Are there other Earth-like
planets, or are we a fluke?
Under what conditions can
Earth-like planets form?
Is life common or rare?
Ways to Find Out
• Look at our own solar system, and think
about how it might have formed
• Look at other solar systems while they
form
• Look for and study other solar systems
• Create computer models and see if you
can produce a solar system
Ways to Find Out
• Look at our own solar system, and think
about how it might have formed
• Look at other solar systems while they
form
• Look for and study other solar systems
• Create computer models and see if you
can produce a solar system
Solar System Geometry
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Terrestrial planets closer than gas/water giants
Planets get smaller beyond Jupiter
Most planets orbit in the same plane
Some small bodies are tilted
Summary of Planetary Interiors
Summary (Things a formation theory must
explain)
•The sun, with most of the system
mass
•Giant planets with solid cores (far from
sun)
•Terrestrial planets (close to sun)
•Most planets orbit in a flat plane
•Many planets have moons
Our theory
• Solar system formation begins because of
gravity - most stuff ends up in the sun
• A disk is formed because of rotation
• Planet cores form in the disk because
rocks hit and/or gravitationally attract each
other
• If there’s ice around (> 5 AU from the star,
where it’s cold) the cores are bigger. If big
enough, they’ll suck gas out of the disk and
form giant planets
• Moons form via collision or capture or in mini
disks
Why might material in clouds collapse to form
stars?
What force keeps clouds from collapsing?
Why might material in clouds collapse to form
stars?
gas pressure
pushes out
(like in a balloon)
What force keeps clouds from collapsing?
Why might material in clouds collapse to form
stars?
What force helps clouds collapse?
Why might material in clouds collapse to form
stars?
gravity pulls inwards
What force helps clouds collapse?
If the cloud is big and cold, gravity will win
out and the cloud will collapse.
gravity pulls inwards
The cloud is spinning.
What happens as it collapses?
(Think of the water in your bathtub drain)
gravity pulls inwards
The cloud spins faster and faster, until it can’t
support itself, and flattens out (think pizza dough)
Lucky for us, this is the perfect way to form a solar
system.
disk = future solar system
blob = future sun
Formation basics
Ways to Find Out
• Look at our own solar system, and think
about how it might have formed
• Look at other solar systems while they
form
• Look for and study other solar systems
• Create computer models and see if you
can produce a solar system
Stars form in Dense Clouds of
Dust and Gas
What do we mean by dust? What do we mean by gas?
The Orion Nebula
Disks really exist!
Disks really exist!
Young stars have asteroid belts
and Kuiper belts
but notice how much bigger this is than the solar system!
In reality, disks are very hard to image.
Why do you think this is?
In reality, disks are very hard to image.
Why do you think this is?
So we usually use spectroscopy to study disks.
Here’s what stars
look like with a
spectrograph.
What would it
look like with
a disk around it?
In reality, disks are very hard to image.
Why do you think this is?
So we usually use spectroscopy to study disks.
Here’s what stars
look like with a
spectrograph.
What would it
look like with
a disk around it?
Disks produce infrared light (just like planets)
Our theory: What do we think now?
• Solar system formation begins because of
gravity - most stuff ends up in the sun
• A disk is formed because of rotation
• Planet cores form in the disk because
rocks hit and/or gravitationally attract each
other
• If there’s ice around (> 5 AU from the star,
where it’s cold) the cores are bigger. If big
enough, they’ll suck gas out of the disk and
form giant planets
• Moons form via collision or capture or in mini
disks
Ways to Find Out
• Look at our own solar system, and think
about how it might have formed
• Look at other solar systems while they
form
• Look for and study other solar systems
• Create computer models and see if you
can produce a solar system
Ways to Find Out
• Look at our own solar system, and think
about how it might have formed
• Look at other solar systems while they
form
• Look for and study other solar systems
• Create computer models and see if you
can produce a solar system
http://www.astronomy.ohio-state.edu/~microfun/ob06109/
Ways to Find Out
• Look at our own solar system, and think
about how it might have formed
• Look at other solar systems while they
form
• Look for and study other solar systems
• Create computer models and see if you
can produce a solar system
Our theory: What do we think now?
• Solar system formation begins because of
gravity - most stuff ends up in the sun
• A disk is formed because of rotation
• Planet cores form in the disk because
rocks hit and/or gravitationally attract each
other
• If there’s ice around (> 5 AU from the star,
where it’s cold) the cores are bigger. If big
enough, they’ll suck gas out of the disk and
form giant planets
• Moons form via collision or capture or in mini
disks
How do you design a computer
simulation?
Why can’t we make a huge computer simulation
to explain everything?
What models would you create?
A model of planets
growing in a disk.
Some things we’ve learned from models:
Our basic theory holds up pretty well, but...
It’s hard to get little particles to stick to each other when
they collide.
It takes a really, really long time to make planets (maybe
too long??)
It’s hard to form planetary systems as flat as ours.
Solar System Formation: Take-away messages
Theory:
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Solar system formation begins because of gravity - most stuff ends up
in the sun
A disk is formed because of rotation
Planet cores form in the disk because rocks hit and/or gravitationally
attract each other
If there’s ice around (> 5 AU from the star, where it’s cold) the cores
are bigger. If big enough, they’ll suck gas out of the disk and form
giant planets
Moons form via collision or capture or in mini disks
Observations generally agree with theory, but it’s hard to see details. They also
show us that stars and disks are all very different from each other. And, they
gave us the surprising observation of outflows.
Simulations also agree with theory, but they can’t model everything at once, and
there are some problems (things take too long, for one)
Is our solar system unique?
Are there other Earth-like planets, or
are we a fluke?
Under what conditions can Earth-like
planets form?
Is life common or rare?