1. Origin of the Solar System Astronomy 311 Professor Lee Carkner Lecture 8

2. Quiz 1 Monday  Covers lectures 1-8 and associated readings  About half multiple choice (~20 questions), half short answer/problems (~4 questions)  Study:  Notes  Can you write a paragraph explaining each major concept?  Exercises  Can you solve all the exercises with no resources?  Readings  Can you do all the homework with no book and Quizdom questions with no notes?  Bring pencil and calculator!  No sharing!

3. The Solar System  Questions   When did it form?   Why does it have structure?

4. Structure of the Solar System  The solar system has three distinct regions   Mercury, Venus, Earth, Mars, Asteroids  Made of metal and rock  Outer region  Jupiter, Saturn, Uranus, Neptune and Moons  Made of ice and gas   Kuiper Belt and Oort Cloud  Made of ice

5. Where Did the Solar System Come From?   We can’t look back in time to see how the Sun and planets formed, but we can look at young stars that are forming today

6. Star Formation   Due to an external stimulus (e.g., supernova shockwave, stellar wind)   Gravity causes the core to contract to a star  Conservation of angular momentum makes the clump spin faster  Rapid rotation causes the outer layers to form a disk

7. Circumstellar Disks  Disks are fairly cool and can be detected with infrared and millimeter telescopes   Disks are common around young stars

8. From Disks to Planets   Where does the disk go?  Formed into planets   Disks you can see, planets you can’t

9. How Do Planets Form?  There are 4 stages to planet formation 11 2  grains stick together to form planetesimals 33 4  gas and leftover planetesimals are cleared from solar system

10. What Was the Solar Nebula Made of?  Solar Nebula --  From studying meteorites and star forming regions we hope to discover what the solar nebula was made of  Two basic components  Gas --  Dust -- made of rock (silicates), metal (iron) and ices (water, methane, ammonia, carbon dioxide)

11. Solar System Dust Grain

12. Accretion of Grains   Grains get larger by sticking together and settle to the center of the disk   Eventually the grains form into larger bodies (a few km in size) called planetesimals  At the end of this stage the solar system is populated by a few thousand planetesimals, such a system is invisible to telescopes

13. Accretion in a Protoplanetary Disk Star Disk High Density Low Density Larger Grains move to center

14. Temperature and the Solar Nebula  Two basic types of dust in solar nebula:  Volatiles --  Refractory Material --  Temperatures were higher in the inner solar system and lower in the outer solar system   Inner solar system -- rocky planetesimals  Outer solar system -- icy planetesimals

15. Regions of Formation Temperature Rocky Icy Gas

16. Planetesimals to Planets  Due to gravity and intersecting orbits the planetesimals collide with each other   Planet formation happens differently in inner and outer solar system

17. Formation of Gas Giants  In the outer solar system you have more material (both volatiles and refractory material), so planets are larger   No more hydrogen gas after a few million years  Thus, in the outer system where the temperatures are lower you have gas giants

18. Formation of Terrestrial Planets   Result is small rocky planets with no large gassy outer layers

19. Accretion of the Inner Planets

20. Orbital Evolution   This causes:  Shifting of the orbits of the Gas Giants   Icy planetesimals ejected to form the Kuiper Belt and Oort cloud

21. The Final Solar System  Our picture of planet formation is driven by an attempt to explain our own solar system and its three regions   Outer or Gas Giant region  Trans-Neptunian or Cometary Region  We have also found other types of planetary systems different from our own 

22. Steps in Solar System Formation 1Inner solar system -- volatiles boil off, resulting in small rocky planets 2Outer solar system -- large planet cores form rapidly from refractory and icy material, acquire large gas envelopes 3Edge of solar system -- leftover and ejected icy planetesimals form Kuiper belt and Oort cloud