1. CH 25.5 Solar System Formation Objectives: How did our solar system form? What evidence supports our ideas? http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html

2. Nebula Theory The solar system formed from a cloud of dust and gas (nebula). 4.6 billion years ago Nebula produced by the explosion of a previous star.

3. Protoplanetary Disk Protoplanetary disk forms when gravity pulls particles and gas to the center. Disk begins to spin (possibly because of a shock wave from a “nearby” supernova. Gravity continues to contract the cloud to the center – making it spin faster (angular momentum … think ice skaters spinning) Protosun at center  Sun when temperatures reach millions of degrees and NUCLEAR FUSION BEGINS. Nuclear fusion combines hydrogen atoms together to make helium and releases LOTS of ENERGY! Stars begin to shine! http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html

4. Planets Grow by Accretion Accretion: Growth by colliding and sticking together Planetessimals (asteroid size)  Protoplanets (moon size)  Planets

5. Inner vs. Outer Inner Solar System = “Rocky” Planets Hotter  Metals & Rock condense (gas  solid) @ higher temps. Outer Solar System = “Gas” Giants Colder  Light gases like H; He; Ammonia; Methane; Water condense (gas  solid ice crystals) @ cold temps.

6. Evidence to Support Sun is 99.9% of mass – in center. Planets all orbit in same plane. Planets orbit in same direction.

7. Summary

8. Extra-solar solar systems