1. HW1 is on-line now and due Tuesday at the beginning of class.
“Arthur Dent had been in some hell holes in his life, but he had never before seen a spaceport that had a sign saying, ‘Even traveling despondently is better than arriving here.’”
The Hitchhiker’s Guide to the Galaxy
Clicker thing
HW1 is on-line now and due Tuesday at the beginning of class.
Questions?

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

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

4. 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

5. 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.

6. 1) mass of planet (more massive planets have more gravity)
If the 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)

7. B) extremely massive gas particles.
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.

8. 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.

9. It points slightly ahead of the Moon.
But the Earth spins faster than the Moon orbits, so the bulge does not point directly at the Moon.
It points slightly ahead of the Moon.

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

11. 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.

12. Laser ranging the Moon

13. 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).

14. 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).

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

16. Consequences:
If the Moon is now slowing down the spin of the Earth. If we go backwards in time, the spin of the Earth would be….

17. The original Earth day (post-Moon creation) was about 10 hours long.
Consequences:
If the Moon is now slowing down the spin of the Earth. If we go backwards in time, the spin of the Earth would be….faster!
The original Earth day (post-Moon creation) was about 10 hours long.
For dinosaurs (65Myrs ago), the day was about 22 hours long. (Confirmed from shellfish and coral growth.)

18. Quiz 2: Which of the following statements is true?
A) The Earth and Moon are the same as they have always been. Nothing changes with time on their surfaces or between them.
B) The Earth and Moon are always changing, especially the Earth’s surface and orbit/spin between the Earth and Moon.
C) The Earth and Moon orbit/spin is changing, but the surfaces of both objects has never changed.
D) Only the Earth’s surface is changing with time, nothing else.

19. 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!!!!

20. 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. Eureka!
Experiments on several satellites 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 impacted into this icy soil in 2010.

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

24. Review of what we’ve learned from the Earth-Moon system.

25. 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.

26. How old is this surface?
A) <few Myrs
B) ~300 Myrs
C) 2 Gyrs
D) 4 Gyrs

27. How old is this surface?
D) 4 Gyrs

28. How old is this surface?
A) <few Myrs
B) ~300 Myrs
C) 2 Gyrs
D) 4 Gyrs

29. How old is this surface?
C) 2 Gyrs

30. Color Variation
1) Composition (different colors made of different stuff)
2) Temperature (solid, liquid, or gas can change color)
3) Altitude (shading)
Well-defined features usually mean solid.
Hazy features usually mean gas.
Smooth (featureless) usually means liquid.

31. A) Solid
B) Liquid
C) Gas

32. C) Gas

33. A) Solid B) Liquid C) Gas

34. A) Solid

35. Solar system Age: 4.6 billion years.
We assume that all objects in our solar system were made at the same time.
So any younger surfaces indicate geologic processes.
Solar system Age: 4.6 billion years.

36. Water: is very common in space.
Tides:
Objects want to be tidally locked. It is the lowest energy state. Smaller things will tidally lock to larger things.
Water: is very common in space.
Surface processes include: plate tectonics, volcanoes, wind/water erosion

37. Bulk properties, not details.
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.
Bulk properties, not details.

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

39. Aside: Kepler's 3 laws of planetary motion
1) Planets travel in elliptical orbits (not circles) with the Sun at one focus.
2) Planets travel faster when they are closer to the Sun, such that a line, connecting the Sun and the planet, sweeps out equal area in equal time.
3) The square of the planet's orbital period is proportional to the cube of the semimajor axis (roughly its orbital distance).

40. Equal area over equal time- means planets travel faster when closer to the Sun and slower when farther away.

41. Another example

43. Square of orbital period = cube of average orbital distance.
P2=a3

44. Starting with the Terrestrial planets.

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

47. Mercury
Old, heavily cratered surface. Probably of similar age as the highlands on the Moon: about 4 billions years old.
Some smooth areas which may be evidence of 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 only 1 km in radius!), cracking the crust.

48. Mercury Density: 5.4 gm/cc Structure
Thin cracked rocky crust
Rocky mantle
Iron core- 75% the size of the planet. Some of the core is probably 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
No moons.

49. 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!

50. Messenger results: Ice in craters (0.1-1 trillion tons of water ice).
Larger Fe core and partially liquid
Magnetic field is uneven (South pole is weaker)
Atmosphere changes with distance.
Surface is sulfur-rich. 10X Earth’s