1. Goal: To understand how our solar system formed and what it like today
Objectives:
Formation of stars
Solar Nebula
Terrestrial Planets
Gas Giants
Other debris
Orbital motions

2. In the beginning All you have is a large cloud of dust and gas.
This cloud is very large and very cold.
They are called Giant Molecular Clouds.
Somehow the cloud
collapses.

3. The initial cloud Is made of mostly Hydrogen (~90% by weight).
Most of the rest is Helium (9%)
1-2% are everything else (in Astronomy we call the everything else “metals” -including Oxygen).
The cloud has some spin. What will that do?

4. Spin city The small amount of spin acts like a merry-go-round.
Much like on a merry-go-round, this spinning motion pushes things outward.
However, nothing stops the collapse in the vertical direction, so the cloud collapses to a disk.
The gas in the disk is literally in orbit around the center of the gas cloud.

5. Disc
The cloud which will form the sun quickly collapses to a spinning disc.
The particles that can get into orbit around the forming star in the middle (called a protostar) survive.
The rest get
gobbled up when
they fall to the
center.

6. Waves Density waves form in the cloud.
These waves will lead to the formation of the planets.

7. Terrestrial Planets The inner part of the disk is hot.
The only materials that can be solid in this heat are rocky materials such as iron and silicon.

8. Tar Line
At some distance carbon compounds can become solid and form tarry substances.
This distance is called the tar line.
There is a lot more carbon than there is iron and silicon in the cloud forming the sun.
So, even though there is less material overall to form a planet at this distance a much larger percentage of it becomes solid.
This allows you to build much larger planets!

9. Ice Line
Similar to the tar line but is the point where materials such as water, ammonia, and methane can freeze.
Since there is a lot more of this than carbon even it allows you to build large planets.

10. Gas Giants – rocky stage
During this stage you start out with small “dirty snowballs”.
These snowballs are half rock and half ice.
In time they fuse with other snowballs to make larger snowballs.
In a few million years they will form the core of a gas giant which is about the size of the earth but ten times the mass of the earth.

11. Run Away Accretion
Once the core of a gas giant becomes 10 earth masses it can capture and hold onto gas.
Most of the gas is Hydrogen and Helium, so this is pretty tough to do.
There is a LOT of gas.
There is far more gas than everything else.
So, at this point it grows very quickly.

12. And they are off to the races!
Since Jupiter was outside the tar line (carbon line) but inside the water line at this time Saturn might have hit the runaway phase first.
Once it did, it was a race against time to gobble up material before the sun is officially born and blasts all the remaining gas out of the solar system.

13. Formation of Major Moons
While gas giants are in their runaway accretion phase they form an accretion disk of dust and gas and ice (similar to the accretion disk around the sun).
Much like planets form around the sun so too would the major moons form around gas giants.

14. Minor Moons
The minor moons would have been captured either during this earliest era where there was a lot of debris and Neptune and Jupiter tossing stuff around.
Others could have been captured comets later.
All orbit the planet backwards (retrograde).

15. Additional debris - asteroids
There are regions of space that do not form planets.
One is our asteroid belt.
In this region gravity from Jupiter would have made rocks that hit each other break each other apart instead of make bigger rocks.

16. Additional debris - TNOs
In the outer solar system just beyond the orbit of Neptune there are objects known as Trans-Neptunian Objects (TNOs).
These did not have enough time to form into a planet.

17. Additional debris – Oort Cloud
Some objects were tossed into enormously large orbits by the gas giants (cough – Jupiter – cough).
These orbits can go out as far as a light year.
This is the source of long period comets.

18. Orbits of Planets
In our solar system all of the planets orbit in the same direction and in the same plane.
The planets are held into place by gravity.

19. Gravity
As you move further from an object the gravity it exerts on you decreases by the distance to its center squared.
So, planets that orbit further from the sun have less gravity exerted on them (in terms of acceleration)

20. Conclusion
We have explored the formation of our solar system and how that affects the composition and distribution of its planets.
We have also explored the basics of our solar system.