1. Cell phones put away and clickers turned on when class begins please.
“The only thing that makes me believe in UFOs is that, sometimes I lose stuff”
Jack Handy
HW1 is on-line now and due next Tuesday at the beginning of class.
Reading updated.
Cell phones put away and clickers turned on when class begins please.
OAAC meeting today 6:30pm in Kemper Hall 101.

2. We determine the surface age of the Earth using radiometric dating
We determine the surface age of the Earth using radiometric dating. Average surface age: 200 million years Oldest Earth rocks: 4.4 billion years Oldest sedimentary rocks: 3.9 billion years

3. Aside: What’s an isotope?
Atoms are made of protons (positive electric charge), neutrons (no electric charge), and electrons (negative electric charge). The number of protons is the atom’s name (H, Fe, Au), but an atom can have different amounts of neutrons. An isotope describes the number of neutrons.

4. The Moon is heavily cratered and the Earth is not
The Moon is heavily cratered and the Earth is not. Because the Earth has lots of erosion.

5. Surface age based on cratering
1) Smothered with craters; the surface is 4+ billion years old. (e.g. Lunar Highlands)
2) medium (-heavy?) cratered; 3.5 billion years old. (e.g. Lunar maria)
3) lightly cratered; ~ million years old. (e.g. Earth's surface)
4) no craters; <few million years old.
This is the yardstick against which all surface ages will be measured.

6. Cratering history.
Late heavy bombardment

7. Assume the same scale for all picturesB
million:
Earth-like
2-3 billion: Maria-like
Assume the same scale for all pictures
Few million:
no craters D C
4-4.5 billion: very nearly saturated

8. How old is the Earth, as a whole. Current estimate: 4
How old is the Earth, as a whole? Current estimate: 4.6 billion years old. Most meteorites are billion years old.

9. The Earth: Multi-colored, round, massive, solid rocky planet with a thin blue-water ocean and white-cloud atmosphere. Green/brown land masses, white polar caps (spin axis nearly aligned with orbital axis) with water/wind weathering, plate
tectonics, and
volcanoes.

10. The Moon: Single color/composition massive, round, rock in space
The Moon: Single color/composition massive, round, rock in space. Solid, heavily cratered surface, no obvious atmosphere, with one side (tidally) locked to the Earth.

11. What about the insides?
How deep into the Earth have we directly sampled?
A) 1% (40 miles)
B) 10% (400 miles)
C) 25% to the center
D) 50% to the center
E) 75% to the center
F) All the way to the center.

12. How deep into the Earth have we directly sampled?
What about the insides?
How deep into the Earth have we directly sampled?
Deepest mine: TauTona- 2.4 miles
0.06% of the way.
Marianas Trench: nearly 6.8 miles deep. 0.17% of the way.
Kola Superdeep Borehole: 7.5 miles deep. 0.19% of the way.

13. What about the insides?
If we haven't directly sampled it, how do we know what is at the center of the Earth, or the Moon?

14. The structure of the Earth using seismology

15. The Earth's structure: Density=5.5g/cc

16. What is the Earth is made of?
Atmosphere: 78% Nitrogen, 21% Oxygen, 1% Argon, 0.03% CO2
Oceans: Water of course, but also salt (Sodium) and Carbon
Crust: Oxygen, Silicon, Aluminium, Iron, Calcium, Sodium
Mantle: Silicates and Magnesium and Iron
Outer Core (liquid): Mostly Iron, some Nickel (4%) and 10% other (mostly Oxygen).
Inner Core (solid): Mostly Iron, same as the outer core.

17. What does this tell us? Crust: Oxygen, Silicon
Mantle: Silicates and Magnesium
Outer Core (liquid): Mostly Iron
Inner Core (solid): Mostly Iron

18. What does this tell us?
That the Earth is differentiated! The heavy stuff settled to the center.
This means the Earth must at one time have been completely molten (liquid).

19. The Moon's structure
Also crust, mantle, and core, but the density is lower
(3.3 g/cc).

20. The Earth-Moon connection
The Moon has exactly the same oxygen isotope ratios as the Earth. Mars, Venus, and asteroids do not.
The composition of the Moon is essentially the same as Earth's crust.
The Earth has a large iron core, the Moon has a very small core
The mean density of the Earth is 5.5g/cc while the Moon's is 3.3g/cc (Note:Water is 1g/cc)

21. How does a planet (any planet!) get a moon?
A more basic question
How does a planet (any planet!) get a moon?

22. What are the consequences of each of these?
How does a planet get a moon?
It forms along with the planet:
Captured:
Split from planet:
Formed from a ring of material that was made by a giant collision.
What are the consequences of each of these?

23. What are the consequences of each of these? Composition and Orbit
How does a planet get a moon?
It forms along with the planet:
Captured:
Split from planet:
Formed from a ring of material that was made by a giant collision.
What are the consequences of each of these?
Composition and Orbit

24. How does a planet get a moon?
It forms along with the planet: Expect orbit to lie in plane of rotation. Orbit should be over spin equator. Composition should be similar (if mass is). Core ratio should be similar.
Captured:
Split from planet:
Formed from a ring of material that was made by a giant collision.

25. How does a planet get a moon?
It forms along with the planet: Expect orbit to lie in plane of rotation. Composition should be similar (if mass is)
Captured: Could have any orbit. Should have same composition as other moons/planets in similar regions. Hard to capture objects into circular orbits.
Split from planet:
Formed from a ring of material that was made by a giant collision.

26. How does a planet get a moon?
It forms along with the planet: Expect orbit to lie in plane of rotation. Composition should be similar (if mass is)
Captured: Could have any orbit. Should have same composition as other moons/planets in similar regions. Hard to capture objects into circular orbits.
Split from planet: Planet spins so fast that a moon is "flung" off the surface. Requires a lot of angular (spin) momentum. The system must keep this momentum. Must orbit over the spin equator. Composition should be that of the crust (no core).
Formed from a ring of material that was made by a giant collision.

27. It forms along with the planet: Expect orbit to lie in plane of rotation. Composition should be similar (if mass is)
Captured: Could have any orbit. Should have same composition as other moons/planets in similar regions. Hard to capture objects into circular orbits.
Split from planet: Planet spins so fast that a moon is "flung" off the surface. Requires a lot of angular (spin) momentum. The system must keep this momentum.
Formed from a ring of material that was made by a giant collision. A lot of parameters: how large were the bodies, at what angle/speed did they hit, what was the conditions on the original bodies at the time?

28. It forms along with the planet: Expect orbit to lie in plane of rotation. Composition should be similar (if mass is)
Captured: Could have any orbit. Should have same composition as other moons/planets in similar regions. Hard to capture objects into circular orbits.
Split from planet: Planet spins so fast that a moon is "flung" off the surface. Requires a lot of angular (spin) momentum. The system must keep this momentum.
Formed from a ring of material that was made by a giant collision.
The best answer is determined by orbit/spin and composition/density.

29. For our Moon: Collision! Evidence:
1) Composition: isotopes found in Moon rocks are similar to Earth's crust, dissimilar to Mars and Venus.
2) Core to crust ratio is too small for simultaneous formation
3) Orbital momentum is too small for the spin-off theory. The Moon's core is too large too.
4) Evidence of ring of molten material around the early Earth.

30. An object about the size of Mars hits the Earth.
Material is ejected high enough to orbit the Earth.
This material forms a ring.
The ring is then gobbled up by the biggest pieces that combine to form the Moon.

33. How do you define an atmosphere?

34. Even if that atmosphere is evaporative.
An atmosphere is a layer of gas that surrounds the central body (planet or moon).
Even if that atmosphere is evaporative.

35. By this definition, our Moon has an atmosphere.
A somewhat controversial conclusion.
Textbook says, “(gravity is) too low to retain an atmosphere.”
The Moon’s atmosphere is evaporative.

36. The Moon is pelted by protons and electrons from the Sun's solar wind
The Moon is pelted by protons and electrons from the Sun's solar wind. These particles free other particles from the Moon's soil. Along with radioactive decay, this produces a thin atmosphere (mostly neon, helium, hydrogen and other stuff).
The Moon's Atmosphere

37. What determines an atmosphere?

38. 1) mass of planet (more massive planets have more gravity)
If they particles of atmosphere move fast enough, they escape into space. This is determined by:
1) mass of planet (more massive planets have more gravity)
2) mass of gas particles (larger particles travel slower)
3) temperature (determines how fast particles move)

39. It is easier to make large molecules when temperatures are cold.
For a hot object (planet/moon) to have an atmosphere, the atmosphere must be a heavy gas or the planet must be massive (high gravity).
For a small object to have an atmosphere, the atmosphere must be a heavy gas, or the planet must be cold.
For an object to have an atmosphere made of light gases, the planet must be massive, or very cold.
It is easier to make large molecules when temperatures are cold.

40. The amazing planet EPIC 228813918b orbits its star every 4. 3 hours
The amazing planet EPIC b orbits its star every 4.3 hours. It is an Earth-massed planet and likely 52% iron with a silicate mantle. If this planet has an atmosphere, it must be:
A) very cold to keep an atmosphere.
B) extremely massive gas particles.
C) extremely light gas particles.
D) very hot to keep an atmosphere.

41. The amazing planet EPIC 228813918b orbits its star every 4. 3 hours
The amazing planet EPIC b orbits its star every 4.3 hours. It is an Earth-massed planet and likely 52% iron with a silicate mantle. If this planet has an atmosphere, it must be:
B) extremely massive gas particles.