1. Formation of the Solar System

2. Formation of the Solar System
From interstellar cloud to planetary system

3. Formation of the Solar Nebula
In a large, slowly rotating cloud of cold gas
Self gravity begins to _________ the cloud
As the cloud gets smaller, it begins to rotate faster, due to ______________ ________________.
Centripetal force prevents gas from collapsing in the plane of rotation
Gas falling from the top collides with gas falling from the bottom and sticks together in the ecliptic plane
collapse
conservation of
angular momentum

4. Formation of the Solar Nebula
In the flat ____________
solar nebula
The densest region of the disk (the center) becomes the _____. Eventually, fusion in the Sun occurs.
Atoms orbiting in the disk bump together and form molecules, such as water. Droplets of these molecules stick together to form ______________.
Over time, the planetesimals grow as more molecules ________ out of the nebula
Sun
planetesimals
condense

5. Formation of the Solar Nebula
Planetesimals grow …
Differential rotation (due to Kepler’s laws) will cause particles in similar orbits to eventually meet up. One will _______ the other, forming a bigger body.
The bigger the body, the greater its gravitational force, and the more attraction it has for other bodies. Further accretion will occur. ___________ form.
accrete
Protoplanets

6. Formation of the Solar Nebula
Material begins to evaporate
While protoplanets are forming, the Sun’s luminosity is growing, first due to gravitational contraction, then due to _____________.
Regions of the nebula close to the Sun will get hot; the outer regions will stay cool. In the hot regions, light elements will __________; only heavy elements will condense out of the nebula
nuclear ignition
evaporate

7. Radiation Pressure and the Solar Wind
Two other processes are also important for driving light gases from the inner part of the solar system.
Radiation pressure
_______________: Photons act like particles and push whatever particles and dust they run into.
Solar wind
_________: The Sun constantly ejects (a little) hydrogen and helium into space. This solar wind pushes whatever gas and dust it runs into.

8. The Pre-Main Sequence Sun
As the Sun formed, it generated a lot of energy via _____________________. During this time, it was brighter than it is today. The radiation pressure in the inner solar system was greater.
In addition, due to conservation of angular momentum, the young Sun was also spinning faster than it is today. This caused the solar wind to be stronger.
gravitational contraction

9. Accretion
Once the major bodies of the solar system were formed, most of the remaining debris was either ejected out of the solar system or accreted onto other bodies by gravitational encounters.

10. Differentiation
Early in the history of the solar system, planets would be molten due to
Continuous accretion of left over material from the solar system formation.
Energy from the fission of radioactive isotopes.

11. Observations of Protostellar Disks
The solar nebula theory states that young stars should be surrounded by a disk consisting of molecular gas and dust. These are now being observed.

12. The Age of the Solar System
We can estimate the age of the Solar System by looking at _________________. These are unstable forms of elements that produce energy by splitting apart.
The radioactivity of an isotope is characterized by its ____ ___ – the time it takes for half of the ______ to decay into its ________ element. By measuring the ratio of the parent to daughter, one can estimate how long the material has been around.
radioactive isotopes
half-
life
parent
daughter

13. Radioactive Elements
Isotope #
protons
neutrons
Daughter
Half-life (years)
Rubidium-87 37 50
Strontium-87
47,000,000,000
Uranium-238 92
146
Lead-206
4,510,000,000
Uranium-235
143
Lead-207
710,000,000
Potassium-40 19 21
Argon-40
1,280,000,000
Aluminum-26 13
Magnesium-26
730,000
Carbon-14 6 8
Nitrogen-14
5,730
Each of these isotopes spontaneously decays into its daughter. In each case, the daughter weighs less than the parent – energy is produced.

14. The solar system is therefore 4.5 billion years old.
Age of the Solar System
When rocks are molten, heavier elements (such as uranium) will separate out from other elements. (In liquids, dense things sink, light things rise.) Once the rocks solidify, radioactive decay will then take over.
On earth, the oldest rocks have ages of __ billion years
The oldest asteroids have ages of ____ billion years
Rocks from the “plains” on the Moon have ages of about 3 billion years. The oldest Moon rocks have ages of 4.5 billion years.
The solar system is therefore 4.5 billion years old. 3
4.5

15. http://www.astro.psu.edu/users/rbc/a1/340,1,Slide 1