Origin of the Solar System

1
Origin of the Solar System

• Astronomy 311
• Professor Lee Carkner
• Lecture 8

2
What would be the easiest way to increase the
magnification of your telescope?

• Increase the size of the primary mirror
• Increase the size of the secondary mirror
• Use an eyepiece with a longer focal length
• Use an eyepiece with a shorter focal length
• There is no way, the magnification of a given
  telescope is fixed

3
Which of the following types of electromagnetic
radiation are best studied from space?

• Ultraviolet
• Radio
• X-ray
• a and c only
• a, b, and c

4
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!

5
The Solar System

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

6
Structure of the Solar System

• The solar system has three distinct regions
• Inner Region
• Mercury, Venus, Earth, Mars, Asteroids
• Outer region
• Jupiter, Saturn, Uranus, Neptune and Moons
• Trans-Neptunian region
• Kuiper Belt and Oort Cloud

7
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

8
Star Formation

• Stars are formed in clouds of gas and dust when a
  clump of material starts to contract
  
• The mutual gravity of the particles in the clump
  causes the contraction to continue
  
• Conservation of angular momentum makes the clump
  spin faster
  
• Rapid rotation causes the outer layers to form a
  disk

9
Circumstellar Disks

• We also can see them silhouetted against a bright
  background in Hubble images
  
• Disks are common around young stars

10
From Disks to Planets

• Many stars between 1-50 million years old have
  disks, but stars slightly older generally do not
  
• Where does the disk go?
• A disk has more surface area than a group of
  planets with the same mass, so it radiates more
  light
  

11
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

12
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)

13
Solar System Dust Grain
14
Accretion of Grains

• Dust grains are very small (form planets?
  
• If dust grains are fractal they may stick
  together more easily
  
• At the end of this stage the solar system is
  populated by a few thousand planetesimals, such a
  system is invisible to telescopes

15
Accretion in a Protoplanetary Disk
Disk
High Density
Low Density
Star
Larger Grains move to center
16
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
  
• Near the Sun the volatiles boiled off leaving
  only the refractory material behind
  
• Outer solar system -- icy planetesimals

17
Regions of Formation
Icy
Rocky
Gas
Temperature
18
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
  

19
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

20
Formation of Terrestrial Planets

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

21
Accretion of the Inner Planets
22
Orbital Evolution

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

23
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
• We have also found other types of planetary
  systems different from our own
  

24
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