Formation of the Solar System

1
Formation of the Solar System

• Many of the characteristics of the planets we
  discussed last week are a direct result of how
  the Solar System formed
  
• Until recently, theories for solar system
  formation were solely based on observations of
  our own system of the Sun and planets
  
• New observations of extra-solar planets are
  expanding our knowledge on the processes involved
  in solar system formation

2
What We Know

• The planets are spaced relatively far from each
  other (no clumps or groups)
  
• _
• The orbits of the planets around the Sun all lie
  nearly in the same plane
  
• _
• The rotation of the planets on their axis is
  usually the same direction (counter-clockwise) as
  their orbit around the Sun

3
What We Know

• Most of the moons in the Solar System orbit their
  planets in a counter-clockwise fashion
  
• _
• Asteroids orbit the Sun similar to the planets,
  but do not share characteristics with either the
  terrestrial or jovian planets
  
• _
• The Oort Cloud contains small icy fragments that
  are distributed in a shell around the Solar System

4
The Explanation

• Astronomers have spent a lot of time and effort
  seeking a theory to explain all ten of the
  previous observations
  
• The theory begins with a cloud of gas and dust
  from which the Solar System can form
  
• The galaxy is full of many such clouds,
  detectable by the light they obscure

New young stars
Dark gas cloud
5
Nebular Contraction

• Something must first trigger the gas cloud to
  collapse
  
• Nearby supernova
• Collision of two clouds
• _
• In addition, as the cloud shrinks, it will begin
  to rotate faster and faster, due to conservation
  of angular momentum

6
Conservation of Angular Momentum

• Many physical quantities in nature must be
  conserved
  
• Mass, energy, and angular momentum cannot be
  created or destroyed, but can be transferred from
  one form to another
  
• _

7
A Spinning Disk

• As the cloud contracts, it spins faster and
  faster
  
• _
• Eventually, the majority of the gas and dust is
  concentrated into a disk

8
Condensation and Accretion

• The central portion of the disk with continue to
  shrink until a star is formed
  
• _
• Small particles of dust begin to collide with
  each other, becoming larger and larger
  
• _

9
Collisions

• Eventually, objects grow to the size of small
  proto-planets
  
• _
• Occasionally, two proto-planets can collide to
  form a new larger body

10
Formation of the Inner Planets
11
The Role of Temperature

• As the planets were forming, there was a wide
  range of temperatures in the solar nebula
  
• _
• Closer toward the Sun, only metals were able to
  survive the high temperatures
  
• _

12
The Role of Temperature

• Mercury, forming very close to the Sun, is
  comprised mainly of metals, like iron
  
• _
• In addition to hydrogen and helium gas, the outer
  planets have high amounts of water and ammonia
  ice
  
• _

13
Where Did the Gas Come From?

• The solar nebula was full of gas, so why did only
  the four outer planets capture huge amounts?
  
• _
• These cores began to sweep up nearby gas (mainly
  hydrogen and helium) very early
  
• _

14
Formation of the Outer Planets
15
Solar System Debris

• While small bodies were colliding and accreting
  in the Solar System, many objects were also
  ejected to more distant orbits
  
• _
• In the inner Solar System, small bodies were
  ejected out to an orbit between Mars and Jupiter,
  forming the asteroid belt
  
• _

16
Kuiper Belt and the Oort Cloud
Early after Gas Giant Formation
After Smaller Bodies Ejected
17
How Did We Do?
?

• The planets are spaced relative far from each
  other (no clumps or groups)
  
• _
• The orbits of the planets around the Sun all lie
  nearly in the same plane
  
• _
• The rotation of the planets on their axis is
  usually the same direction (counter-clockwise) as
  their orbit around the Sun

?
?
?
?
18
How Did We Do?
?

• Most of the moons in the Solar System orbit their
  planets in a counter-clockwise fashion
  
• _
• Asteroids orbit the Sun similar to the planets,
  but do not share characteristics with either the
  terrestrial or jovian planets
  
• The Kuiper belt contains a large collection of
  icy objects outside the orbit of Neptune
  
• _

?
?
?
?
19
What About the Exceptions?

• There are a few objects in the Solar System which
  do not follow the 10 observations we listed
  
• _
• Uranus' axis is tilted by more than 90o
• A glancing collision early in its history could
  have knocked Uranus on its side

20
Formation of Earth's Moon

• It is also believed that a collision between
  proto-Earth and a Mars-sized proto-planet created
  our Moon
  
• Computer models can reproduced this situation
• _