Origin of the Solar System

1
Origin of the Solar System

• Astronomy 311
• Professor Lee Carkner
• Lecture 8

2
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!

3
The Solar System

• Questions
• When did it form?
• Why does it have structure?

4
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

5
Where Did the Solar System Come From?

• We cant look back in time to see how the Sun and
  planets formed, but we can look at young stars
  that are forming today

6
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

7
Circumstellar Disks

• Disks are fairly cool and can be detected with
  infrared and millimeter telescopes
• Disks are common around young stars

8
From Disks to Planets

• Where does the disk go?
• Formed into planets
• Disks you can see, planets you cant

9
How Do Planets Form?

• There are 4 stages to planet formation
• ?
• ? grains stick together to form
  planetesimals
• ?
• ? gas and leftover planetesimals are
  cleared from solar system

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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)

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Solar System Dust Grain
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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

13
Accretion in a Protoplanetary Disk
Disk
High Density
Low Density
Star
Larger Grains move to center
14
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

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Regions of Formation
Icy
Rocky
Gas
Temperature
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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

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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

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Formation of Terrestrial Planets

• Result is small rocky planets with no large gassy
  outer layers

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Accretion of the Inner Planets
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Orbital Evolution

• This causes
• Shifting of the orbits of the Gas Giants
• Icy planetesimals ejected to form the Kuiper Belt
  and Oort cloud

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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

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Steps in Solar System Formation

• Inner solar system -- volatiles boil off,
  resulting in small rocky planets
• Outer solar system -- large planet cores form
  rapidly from refractory and icy material, acquire
  large gas envelopes
• Edge of solar system -- leftover and ejected icy
  planetesimals form Kuiper belt and Oort cloud