1. Inner Planetary Geology I

2. Terrestrial Planets  The Terrestrial Planets cooled from molten masses  Acquired structure during cooling  Made primarily of rock and metal

3. Larger Worlds are Round Phobos (One of Mars’ two moons) Diameter: ~ 11 miles Earth Diameter: 8000 miles NOT ROUNDROUND

4. Larger Worlds are Round  From the book (p. 260): Gravity will make any rocky object bigger than about 310 miles into a sphere within about 1 billion years.

5. What’s inside a planet?  How do we find out what’s inside? We have drilled less than 1% toward Earth’s center ○ Russians drilled 7 miles into the crust! ○ 356 o F, drill wasn’t working well  What goes on inside affects what happens on the surface

6. Seismology  Spectroscopists use spectra to probe atoms and molecules  Seismologists use seismic waves to probe the interior of Earth  On other planets, we’ve only looked at rocks

7. Seismic Waves  Speed and direction of seismic waves depends on: Composition Density Pressure Temperature Solid / Liquid  Send in some waves, see what you get back.

8. Seismic Waves  Waves are disturbances of a medium  Two types of waves: Longitudinal Transverse  With seismic waves, Earth vibrates as the spring does

9. Seismic Waves  Longitudinal waves: Go through almost any material in any phase ○ Solids, liquids, and gases  Transverse waves: Inside Earth, only travel through solids

10. Seismic Waves  So what does it mean when: Longitudinal waves from an earthquake reach the other side of the world, while transverse waves do not?

11. Seismic Waves  It means that Earth has some liquid.  Can figure out the extent via geometry of transmitted / reflected waves

12. Structure of Terrestrial Planets Earth’s crust: 30 miles thick Earth’s mantle: 2000 miles thick Earth’s core: 2000 miles thick Mantle is mostly solid! Lithosphere is cool and rigid.

13. Why is it layered?  When Earth formed, it was hot! Mostly liquid  Gravity pulled the heavier elements closer to the center  This is called differentiation.

14. Strength of Rock  Rock will deform if: You heat it and You subject it to sustained stress  “Sustained stress” can come from gravity  The rock under the lithosphere is warm and soft (NOT LIQUID). It acts like a really thick sludge!

15. Geological Activity  Change that occurs on the surface Volcanoes Earthquakes Erosion  Results from interior heat reaching the surface Things expand and contract Things melt and flow  Geological activity requires: Mantle convection A thin lithosphere

16. Interiors: Heating  Planetary interiors have lots of thermal energy This energy does NOT come from the Sun! Comes from: ○ Heat of accretion (planet formation) ○ Heat from differentiation (heavier materials moving inward) ○ Heat from radioactive decay

17. Interiors: Heating  Which of the following processes are definitely NOT adding thermal energy to Earth today? ○ Heat of accretion? ○ Heat from differentiation? ○ Heat from radioactive decay?

18. Interiors: Cooling  Mantle convection Hot rock is less dense It gets forced upward  Conduction Inefficient heat exchange via direct contact between mantle and lithosphere  Surface radiation Atoms and molecules give up internal energy as EM waves

19. Interiors: Cooling  Is there evidence that mantle convection is happening today?  Does Earth’s surface radiate energy away? Why or why not? (Think of what causes a continuous spectrum.)

20. Geological Activity  As the interior cools over millions of years: Lithosphere thickens toward the core ○ Acts as thermal insulation Stops convection  Larger planets hold more energy and don’t radiate it as well

21. Geological Activity Larger planets stay geologically active longer.

22. Geological Activity  Is Earth geologically active?  Is the Moon geologically active?  Is Mercury geologically active?

23. Geological Activity Earth still has enough warmth in its core to maintain convection. This keeps the lithosphere thin and warm, so heat can reach the surface. This is why Earth is geologically active.

24. Geological Activity The Moon and Mercury couldn’t generate enough heat to maintain convection. Their lithospheres solidified and geological activity ceased.

25. Magnetic Fields  Moving charges in the liquid outer core create a magnetic field  Loss of heat can solidify the core Loss of mag-field  Can look at a planet’s mag. field to learn about liquid core

26. Planetary Surfaces  Impact cratering Asteroid / comet strikes  Impacts occur around 24,000 – 155,000 mph

27. Planetary Surfaces

28. “Standard”Muddy?Eroded by wind / rain? (All on Mars.)

29. Planetary Surfaces Craters give a very good indication of how geologically active a surface is. This is because geological activity erases craters.

30. Geological Age and Craters

31. Planetary Surfaces  Why are Mercury and the Moon covered in craters, but Earth is not? (Two reasons.)

32. Planetary Surfaces  Volcanism Hot, liquid rock (magma) comes up to the surface Solid rock may squeeze molten rock out Trapped gases often expand as the magma rises

33. Planetary Surfaces Volcanic plains: “runny” lava flow Shield volcanoes: thicker flow, solidify before they can spread out much Stratovolcanoes: thickest lava flows. Hardly spreads before solidifying.

34. Planetary Surfaces  Tectonics Stretching, compressing, reshaping lithosphere Caused mainly by mantle convection

35. Planetary Surfaces  Erosion Breaking down / transporting rock via wind or liquid flow More eroded surfaces are older