1. Announcements 25 people have still not joined the class on Astronomy Place. You can not get credit until you “join the class”. Once you join, all your previous submissions will show up in my gradebook. Planet Assignment 4, due Monday March 1, –Part 1: Astronomy Place tutorial “Shaping Planetary Surfaces” –Part 2: Angel Planet Assignment 4

2. Example of a proto-Planetary Disk

3. Objectives: Describe the significance of bombardment in the early solar system. Compare and contrast the structure & evolution of the terrestrial planets. Describe the differentiation into core, mantle & crust. Describe the heating and cooling processes in planetary interiors. Describe the importance of planetary size on its evolution.

4. Two Types of Planets Terrestrial: small rocky, iron inner Jovian: large H, He, ices outer

5. When Planets Form - Bombardment & Differentiation Bombardment of planet as it forms, HEATS and melts its surface Molten iron and other heavy elements sink toward the center Falling iron converts gravitational potential energy to kinetic energy -> HEAT

6. Inside the Terrestrial Worlds After they have formed, the molten planets differentiate into three zones: core - made of metals mantle - made of dense rock crust - made of less dense rock Lithosphere - the rigid, outer layer of crust & part of the mantle which does not deform easily

7. Inside the Terrestrial Worlds

8. Heating the Planets Planetary interiors heat up through: accretion differentiation radioactivity Supplies all the heat at the beginning Supplies heat throughout the planet’s life

10. Cooling the Planets Planets Cool by Radiating Heat to Space from their Surface Heat is Transported from the Interior to the Surface by: conduction - atoms & molecules moving & hitting other atoms & molecules convection - macroscopic flows: hot material rising & cool material sinking

11. Convection

12. Cooling Terrestrial Planets

13. Role of Planetary SIZE Larger planets heat more –More iron to flow to center –More radioactive elements to split Larger planets cool slower –Extra layers provide extra insulation

14. Role of Planetary Size Heating proportional to Volume ~ R 3 Cooling proportional to Surface Area ~ R 2 Heating/Cooling ~ Volume/Area ~ R = Size Smaller Planets Cool Faster & Heat Less (by impacts and splitting of radioactive nuclei) -> Thicker rigid Lithosphere -> Less volcanism & Tectonic Activity

15. Inside the Terrestrial Worlds active geologyinactive geology

16. How do we Know about the Interior of Earth Earthquakes make waves Waves travel through Earth, the higher the density the faster the waves travel Two types of waves –Back & forth –Side to side

17. Shaping Planetary Surfaces Major geological processes that shape planetary surfaces: impact cratering: excavation of surface by asteroids or comets striking the planet volcanism: eruption of lava from interior tectonics: disruption of lithosphere by internal stresses erosion: wearing down by wind, water, ice

18. Counting Craters to find Surface Age Cratering rate decreased as Solar Systems aged. The older the surface, the more craters are present.

19. Impact Craters - Mars

20. Volcanism - Mars Olympus Mons

21. Olympus Mons

22. Volcanism - Venus

23. Plate Tectonics

24. History of Plate Tectonics South America and Africa fit together like a jig-saw puzzle, with matching geological formations and fossils New Idea (Wegner 1912) Continental Drift Rejected by Geologists –Counter to established ideas –Lack of overwhelming evidence –No mechanism to drive motions

25. Evidence

26. Mid-Atlantic Rift in Iceland Division between North American & European Plates

27. Mechanism - Mantle Convection

29. Earth’s Plates

30. Earth’s Plate Motion

31. Valles Marinares - Mars

32. Erosion Mars Evidence for water in past

33. Erosion Wind

34. Summary