1. Our Solar System and Its Origin
How was the Solar System Formed?
A practical 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 MOST of the observable facts with reasonable accuracy
able to explain other planetary systems.

2. What does the solar system look like from far away?
NASA Figure
1. Sun: a star, at the center
2. Inner Planets (Mercury, Venus, Earth, Mars)
a. rocky
b. dense
c. small
d. few moons
e. no rings
f. Distance ~1AU
Cool link about solar system:

3. Summary - What do the inner planets look like?

4. 4. Outer Planets (Jupiter, Saturn, Neptune, Uranus) a. gaseous
Continued…
3. Asteroid Belt: ~ 3 AU
4. Outer Planets (Jupiter, Saturn, Neptune, Uranus)
a. gaseous
b. less dense
c. large
d. many moons
e. all have rings
f. ~ 5-40 AU
5. Pluto: dwarf planet- more like a comet

5. Summary - The Jovian Planets

6. Quantitative Planetary Facts

7. Terrestrial and Jovian Planets

8. The Kuiper Belt and the Oort Cloud
6. Kuiper Belt (~30 to 50 AU):
A large body of small objects (short period comets) orbiting the Sun in a radial zone extending outward from the orbit of Neptune (30 AU) to about 50 AU. Pluto may be the biggest of the Kuiper Belt object.
NASA Figure

9.
7. Oort Cloud (~ 50,000 AU)
Long Period Comets (period > 200 years) seems to come mostly from a spherical region at about 50,000 AU from the Sun.

10. Common Characteristics and Exceptions of the Solar System

11. Common Characteristics and Exceptions

12. Hypotheses to explain the formation of the solar system
1. Gravitational Collapse of Planetary Nebula (Latin for “cloud”) Solar system formed from gravitational collapse of an interstellar cloud or gas

13. 2. Close Encounter (of the Sun with another star)
Planets are formed from debris pulled out of the Sun during a close encounter with another star. But…
Probability for such encounter is small in our neighborhood

14. 3. 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

15. Gravitational Collapse
A Pictorial History
Gravitational Collapse
Interplanetary Cloud
Condensation
Accretion
Nebular Capture
Accretion: the coming together and cohesion of matter under the influence of gravitation to form larger bodies.

16. The Interstellar Clouds
The primordial gas after the Big Bang has very low heavy metal content
The interstellar clouds that the solar system was built from gas that has gone through several star-gas-star cycles

17. Collapse of the Solar Nebula
Gravitational Collapse
Denser region in a interstellar cloud, maybe compressed by shock waves from an exploding supernova, triggers the gravitational collapse.
Heating  Prototsun  Sun
In-falling materials loses gravitational potential energy, which were converted into kinetic energy. The dense materials collides with each other, causing the gas to heat up. Once the temperature and density gets high enough for nuclear fusion to start, a star is born.

18. This process explains the orderly motion of
2. Spinning  Smoothing of the random motions
Conservation of angular momentum causes the in- falling material to spin faster and faster as they get closer to the center of the collapsing cloud.
3. Flattening  Protoplanetary disk.
The solar nebular flattened into a flat disk. Collision between clumps of material turns the random, chaotic motion into a orderly rotating disk.
This process explains the orderly motion of
most of the solar system objects!