1. Chapter 6 Our Solar System and Its Origin
How was the Solar System Formed?
A viable theory for the formation of the solar system must be
based on physical principles (conservation of energy, momentum, the law of gravity, the law of motions, etc.),
able to explain all (at least most) the observable facts with reasonable accuracy, and
able to explain other planetary systems.
How do we go about finding the answers?
Observe: looking for clues
Guess: come up with some explanations
Test it: see if our guess explains everything (or most of it)
Try again: if it doesn’t quite work, go back to step 2.

2. What does the solar system look like from far away?
NASA Figure
Sun, a star, at the center…
Inner Planets (Mercury, Venus, Earth, Mars) ~ 1 AU
They are all rocky planets…
Asteroid Belt, ~ 3 AU
Outer Planets (Jupiter, Saturn, Neptune, Uranus), ~ 5-40 AU
They are all gaseous planets..
Pluto: odd ball planet, more like a comet…
Keiper Belt ~ 30 to 50 AU
Oort Cloud ~ 50,000 AU
Where comets come from…
Cool link about solar system:

3. Clues - The Orbits of the Planets
All the planets orbit the Sun in the same direction
The rotation axes of most of the planets and the Sun are roughly aligned with the rotation axes of their orbits.
Orientation of Venus, Uranus, and Pluto’s spin axes are not similar to that of the Sun and other planets.
Why do they spin in roughly the same orientation?
Why are they different?

4. Summary - What do the inner planets look like?
They are all…
rocky and small!
No or few moons
No rings

5. Summary - The Jovian Planets
They are all…
gaseous and BIG!
Rings
Many moons

6. Common Characteristics and Exceptions of the Solar System
We need to be able to explain all these!

7. The Nebular Theory* of Solar System Formation
Interstellar Cloud (Nebula)
*It is also called the ‘Protoplanet Theory’.
Protoplanetary Disk
Protosun
Gravitational Collapse
Metal, Rocks
Condensation (gas to solid)
Sun
Gases, Ice
Heating  Fusion
Terrestrial Planets
Accretion
Nebular Capture
Jovian Planets
Asteroids
Leftover Materials
Comets
Leftover Materials

8. It starts from a Nebula…
Nebula- large cloud of gas and dust
Mostly Hydrogen and Helium
P.O.C- (light years in length)
Horsehead Nebula (Infrared Image)

9. Why are they there in the first place?
Carina Nebula
Lagoon Nebula

11. Supernovas or Novas
Supernova- an explosion from the result of the death of a star
Provides material (elements) for nebulae
The Helix Nebula (Recognize it?)
Infrared Light
Crab Nebula- a supernova remnant
(Visible light)

12. 1. Gravitational Collapse
Thought to be started by a Supernova
OR thought to be started by overdensity
Starts very slowly at first, but as it collapses the rotation begins to move faster…

13. Conservation of Angular Momentum
Spinning speed increases as you move mass towards the middle

14. Collapse Continued
As collapse furthers, speed increases and kinetic energy increases
Faster particles start ‘dominating’ the direction of the spin, force others to go in their direction
Remember this video (2:50)

16. Why all planets revolve,rotate in the same direction
This explains…
Why all planets revolve,rotate in the same direction

17. 2. Protosun (Part B in pic)
Eventually, the collapse causes a huge increase in heat and pressure
Fusion begins, and a sun formed in the middle of the cloud

18. 3. Protoplanetary Disk
The rest of the cloud that didn’t form the sun Why is it all on the same plane? (Part B&C)

19. Same reasons as the physics of this…

20. Or this…

21. Why all the planets exist on the same plane
This explains...
Why all the planets exist on the same plane

22. 4. and 5. Condensation/Accretion
Condensation: Gas turning into liquid or solid particles due to cooling
Accretion: Process in which liquid/solid particles ‘stick together’ and form larger pieces
Planetesimals: Small, planet-like bodies formed from accretion

23. The Nebular Theory* of Solar System Formation
Interstellar Cloud (Nebula)
*It is also called the ‘Protoplanet Theory’.
Protoplanetary Disk
Protosun
Gravitational Collapse
Metal, Rocks
Condensation (gas to solid)
Sun
Gases, Ice
Heating  Fusion
Terrestrial Planets
Accretion
Nebular Capture
Jovian Planets
Asteroids
Leftover Materials
Comets
Leftover Materials

24. Gravitational Collapse
A Pictorial History
Gravitational Collapse
Interplanetary Cloud
Condensation
Accretion
Nebular Capture

25. Asteroid Belt
Asteroid Belt: Leftover material within the frost line that did not accrete into a planet
Frost line: Area within which heavy metals can condense into liquid/solids (3.5 AU)
Inside frost line = metallic elements
Outside frost line = hydrogen compounds, helium, hydrogen

26. Why no accretion?

27. Jovian Planet Formation: Step by Step
Accretion- Just like terrestrial planets, only this material is composed of hydrogen compounds (Water, Methane)
Planetesimals are much LARGER than terrestrial planetesimals. Why?
(Think composition)

28. 3. Nebular Capture
3. Nebular capture- Gases being ‘captured’ by Jovian planets’ gravitational pull
Nebular capture happens after accretion

29. Nebular capture More mass = more gravity
Planets have enough mass to attract hydrogen and helium gas
Remember- 71% Hydrogren

30. In conclusion… Accretion of icy compounds
Planetesimals became massive enough to attract hydrogen and helium
Planetesimals attracted TONS of the two gases through nebular capture
Jovian Planets formed

31. Terrestrial Planets?
Did not attract Hydrogen and Helium because their mass was much too low to attract Hydrogen and Helium (Two lightest elements)
So they do not have a large gaseous area of these two gases
Explains size difference

32. Kuiper Belt

33. Kuiper Belt Similar to asteroid belt…
“Dirty snowball-” an asteroid with icy compounds on it
Leftover material that did not accrete into a jovian planet

34. In summary…