1. Xi Zhang E&MS A261 <xiz@ucsc.edu>
Planetary Discovery
in the era of Spacecraft Exploration
Xi Zhang
E&MS A261
TA: Szilard Gyalay

2. Today’s Outline Mid-term on next Friday Planetary Formation (Chap. 8)
Surface and Interior of Terrestrial Planets (Chap. 9)

3. Mid-Term (1) Next Friday (Nov. 3), 10:40-11:45 am
Same time, same place
Materials: week 1 – next Wed (read your textbook!). See topics in your box.
Close book and close note
No smartphones allowed
A small calculator is allowed, but the math can be readily done without them
~50 multiple choice questions
Equation sheet will be provided 3

4. Mid-Term (2) Bring a #2 pencil Know your Student ID
Bring a PINK scantron score sheet
TA and me will proctor the Exam
TA will have review sessions next week 4

6. What properties of our solar system must a formation theory explain?
Patterns of motion of the large bodies
Orbit in same direction and plane
Existence of two types of planets
Terrestrial and jovian
Existence of smaller bodies
Asteroids and comets
Notable exceptions to usual patterns
Rotation of Uranus, Earth's Moon, etc.

7. Nebular Theory Collapse (initiated by supernova?)
Heating, Flattening, and
spinning up
Condensation (Ice and rock)
Accretion of planetesimals
Solar Wind stripping of gas
Sun ignites!

8. Frost Line (or Snow Line)
Inside the frost line: too hot for hydrogen compounds to form ices
Outside the frost line: cold enough for ices to form
Question: Would the Jovian planets have formed closer to the sun or farther in the disk if the solar nebula had cooled, with a temperature half its actual value?

9. Asteroids and Comets Leftovers from the accretion process
Rocky asteroids inside frost line
Icy comets outside frost line

10. Heavy Bombardment
Leftover planetesimals bombarded other objects in the late stages of solar system formation.
Impact cratering

11. Origin of Earth's Water
Water may have come to Earth by way of icy planetesimals.
Or degassing from the interior

12. Moons of jovian planets
Moons of jovian planets form in miniature disks.

13. Captured Moons
These are Phobos and Deimos, respectively.
Unusual moons of some planets may be captured planetesimals.
Mars moons have similar compositions with the asteroids.

14. Story of our Moon: Giant Impact
Credit: Miki Nakagima
Credit: Robin Canup

15. Odd Rotation
Giant impacts might also explain the different rotation axes of some planets.

16. Collapse (initiated by supernova?)
Heating, Flattening, and
spinning up
Condensation (Ice and rock)
Accretion of planetesimals
Solar Wind stripping of gas
Sun ignites!

17. Was our solar system destined to be?
Formation of planets in the solar nebula seems inevitable.
But details of individual planets could have been different.

18. What caused the orderly patterns of motion in our solar system?
Solar nebula spun faster as it contracted because of conservation of angular momentum.
Collisions between gas particles then caused the nebula to flatten into a disk.
Why are there two major types of planets?
Only rock and metals condensed inside the frost line.
Rock, metals, and ices condensed outside the frost line.
Larger planetesimals outside the frost line drew in H and He gas.

19. Where did asteroids and comets come from?
They are leftover planetesimals, according to the nebular theory.
How do we explain "exceptions to the rules"?
Bombardment of newly formed planets by planetesimals may explain the exceptions.

20. Surface and Interior of Terrestrial Planets

21. Earth's Interior Core: highest density; nickel and iron
Mantle: moderate density; silicon, oxygen, etc.
Crust: lowest density; granite, basalt, etc.

22. Terrestrial Planet Interiors
Applying what we have learned about Earth's interior to other planets tells us what their interiors are probably like.

23. Differentiation Gravity pulls high-density material to center.
Lower-density material rises to surface.
Material ends up separated by density.

24. Lithosphere
A planet's outer layer of cool, rigid rock is called the lithosphere.
It "floats" on the warmer, softer rock that lies beneath.

25. Earth’s Interior Structure

26. Strength of Rock
Rock stretches when pulled slowly but breaks when pulled rapidly.
The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.

27. Special Topic: Seismic Waves
How do we know what's inside Earth?
Vibrations that travel through Earth's interior tell us what Earth is like on the inside.
P waves push matter back and forth.
S waves shake matter side to side

28. Seismic Waves P waves go through Earth's core, but S waves do not.
We conclude that Earth's core must have a liquid outer layer.

29. Seismic Waves in Earthquakes
Seismogram of the 1906 earthquake recorded in Germany
An earthquake is caused by sudden movement on a sub-surface fault.
The energy which is released (which was stored as strain in the rock) is converted to seismic waves which radiate from the earthquake focus.
These seismic waves cause ground shaking and can be measured using seismometers.
San Francisco 1906 (USGS)

30. Quiz What is necessary for differentiation to occur in a planet?
A. It must have metal and rock in it.
B. It must be a mix of materials of different density.
C. Material inside must be able to flow.
D. All of the above
E. B and C
怨毒的告密者”
怨毒的告密者”

31. Causes of geological activity

32. Heating of Planetary Interiors
Accretion and differentiation when planets were young
Radioactive decay is most important heat source today.