1. Cell phones put away and clickers turned on when class begins please.
“Between impulse and action, there is a realm of good taste begging for your acquaintance.”
The Doctor, Star Trek Voyager
HW1 on-line now and due in 1 week.
Cell phones put away and clickers turned on when class begins please.

2. The Earth-Moon system.

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

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

5. Each has consequences, mostly related to Composition and Orbit
There are multiple ways to make/get moons.
Each has consequences, mostly related to
Composition and Orbit

6. An atmosphere is a layer of gas that surrounds the central body (planet or moon). Even if that atmosphere is evaporative.
Atmospheres are determined by:
1) Temperature
2) mass of the gas particles (heavier moves slower)
3) mass of the object (planet/moon/etc.) -escape velocity
Atmosphere

7. What determines an atmosphere?

9. Tides
The Moon's gravity pulls the Earth. At the middle, it's pulled straight, but at the poles, it's pulled slightly inward.
This squeezes the Earth and makes tides.
The same occurs for some other planets/moons.

10. But the Earth spins faster than the Moon orbits, so the bulge does not point directly at the Moon.

11. Consequences:
The bulge is a forward pull on the Moon's orbit and a backwards pull on the Earth's spin.

12. Consequences:
The bulge is a forward pull on the Moon's orbit and a backwards pull on the Earth's spin.
The Moon's orbit is getting larger (the Moon's distance increases about 3 cm/year) and therefore longer.

13. Laser ranging the Moon

14. Consequences:
The bulge is a forward pull on the Moon's orbit and a backwards pull on the Earth's spin.
The Earth's spin is slowing, so days are getting longer (1.5 msec/century).

15. Consequences:
The bulge is a forward pull on the Moon's orbit and a backwards pull on the Earth's spin.
Eventually, the Earth will be tidally locked to the Moon, just as the Moon is tidally locked to the Earth. Then, 1 Earth day will equal 1 Moon orbit (about 30 current Earth days).

16. The Moon is tidally locked to the Earth: It spins at the same rate of its orbit. So 1 side always faces the Earth.

17. Consequences: Working backwards in time.
The original Earth day (post-Moon creation) was about 10 hours long.
For dinosaurs, the day was about 22 hours long. (Confirmed from shellfish.)

18. The Earth-Moon system is dynamic
The Earth-Moon system is dynamic. It seems like it is constant, but it is always changing.
Similarly, our solar system seems like the same ol' thing. But in fact it is in the process of changing all the time!!!!

19. Water on the Moon?
There are areas on the Moon that never receive direct sunlight. IF ice can get in there, it will not evaporate.

21. L-Cross then impacted into this icy soil in 2010.
Eureka!
Experiments on Clementine and Lunar Prospector detected the signature of water on both the North and South Poles of the Moon.
Each pole possibly contains at least a small-ish lake's worth of water-ice.
L-Cross then impacted into this icy soil in 2010.

23. Where did all that water come from?
Possibly from comets in the early solar system.

24. D) lighter in weight (less massive).
Quiz 2:
Our Moon is getting...
A) closer to us.
B) farther from us.
C) free from our orbit.
D) lighter in weight (less massive).

25. The Earth: Colorful, solid rocky planet with a thin blue-water ocean and white-cloud atmosphere. Blue/brown land masses, white polar caps (spin axis nearly aligned with orbital axis).
Water/wind weathering,
plate tectonics, volcanoes.
Life!
Round, so massive.

26. The Moon: Not colorful massive, round, rock in space
The Moon: Not colorful massive, round, rock in space. Solid, heavily cratered surface. One side (tidally) locked to the Earth. No obvious atmosphere.

27. 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.

28. Color Variation
1) Composition (different colors made of different stuff)
2) Temperature (solid, liquid, or gas can change color)
3) Altitude (shading)

29. Tides: Objects want to be tidally locked. It is the lowest energy state. Smaller things will tidally lock to larger things.

30. Now that we have our baseline. It's time to explore our solar system!!

31. Starting with the Terrestrial planets.

32. Mercury What do you see and what does it mean?

34. Altitude map

35. Mercury
Old, heavily cratered surface. Probably of similar age as the highlands on the Moon: about 4 billions years old.
Some smooth areas which were caused by later volcanism (lava flows, like the mare on the Moon).
Globally cracked surface indicates that Mercury's surface solidified first (as expected) and as the mantle solidified, Mercury shrank slightly (by up to 7 km in radius!), cracking the crust.

36. Mercury Density: 5.4 gm/cc Structure
Thin cracked rocky crust
Rocky mantle
Iron core- 85% the size of the planet. Some of the core is molten (liquid).
Temperature: Daytime 441F, Night -279F
Atmosphere (yes, it has one!): Thin atmosphere created by solar wind blasting the surface (made of sodium mostly). It evaporates into space. 1 trillionth of Earth's pressure

37. Mercury, Unusual Spin/Orbit 3:2 Spin/Orbit resonance.
One sidereal day is 59 Earth days.
One solar day is 176 Earth days.
One orbital period is 88 Earth days.
This is a form of tidal locking!

38. Information from Mercury Messenger.
Orange areas (and white arrows) are iron-deficient lavas. Black areas are explosive volcanoes. Blue regions are iron-bearing minerals.
Information from Mercury Messenger.

39. 2) Mercury's magnetic field is 100X smaller than the Earth's.
Mercury Messenger:
Results:
1) Mercury formed with less oxygen and more sulfur (10x) than Venus, Earth, or Mars.
2) Mercury's magnetic field is 100X smaller than the Earth's.

40. Mercury Messenger Results:
3) Mercury has water-ice at the poles in craters.

41. Mercury's
structure
Still cooling and shrinking