1. Terrestrial Planets

4. Planetary size and heat loss
Large planets retain internal heat longer
Small planets cool off quickly

6. Geologic processes
Impact cratering
Volcanism
Tectonics
Erosion

7. Discussion
The Moon has lots of impact craters, while the Earth has very few. Why do you think there is a difference?

8. Surface age
The more impact craters on a surface, the older that surface is.
The age of a surface refers to when that surface solidified.

9. Discussion
Which area on the Moon is older, the light region to the left or the dark region in the center of the picture?

11. Discussion
Why do you think a more heavily cratered planetary surface is older than a smooth one?

12. Why?
All the terrestrial planets probably receive about the same number and size distribution of impacts. All the other geologic processes (volcanism, tectonics, and erosion) tend to erase impact craters on the surface.

13. Discussion
Rank the terrestrial planets (include the Moon) in terms of the age of their surfaces from youngest to oldest to try and predict which planets will have the most craters.
Size ranking

14. Earth
Venus
Mars
Mercury
Moon
Smaller planets retain less heat and therefore have less geologic activity.

22. Discussion
Almost all impact creators are round. Why do you think there are not many elliptically shaped craters?

23. Almost all impact craters are round
In general, impactors will hit with a velocity greater than the escape velocity. The high speed collision results in the almost complete vaporization of the impactor. This explosion of super-heated, vaporized rock is what creates the crater.

26. Moltke Crater (7 km)

27. Bessel crater (16 km)

28. Euler Crater (25 km)

29. King Crater (77 km)

30. Copernicus Crater (95 km)

31. Schrodinger (320 km)

32. Mare Orientale (930 km)

33. Mare Imbrium (1100 km)
Mare Imbrium

34. Meteor Crater (1.2 km)

35. Arizona from the Shuttle

36. Wolf Creek (0.85 km)

37. New Quebec Crater (3.4 km)

38. Clearwater Lakes (26 km)

39. Chichxulub Crater (250 km)

40. Manicouagan Crater (100 km)

41. Discussion
Why is the Manicouagan crater inverted, with a lower rim and higher center?
Hint: It is at high northern latitude and is rather old.

42. Radar images of Venus
Bright areas in radar images indicate rough terrain, while dark areas are smooth. Typically, rough terrain is younger than smooth terrain.

43. Discussion
Why are rough areas younger?

44. Adivar Venus (29 km)

45. Meitner basin Venus (150 km)

47. Discussion
What does the fact that there are so few eroded craters tell you about Venus?

48. Plate Tectonics

51. No plate tectonics on Venus
Venus may not have an asthenosphere, due to the lack of water in Venus’s mantle.
Alternatively, the crust of Venus may be too plastic to form large-scale faults.

56. Colaris basin Mercury (1340 km)

58. Hellas basin Mars (2000 km)

59. 7 km deep, Height of Mt Everest 8.8 km

61. Discussion
Notice anything unusual about this crater on Mars? What can you conclude about the surface of Mars where this crater formed?

62. Why are craters important
Numbers of craters provide relative ages
Transition size between simple and complex craters as well as ejecta blanket size and distribution provide clues to the strength of the surface.

63. Liquid Water All life on Earth depends on liquid water.
Earth is the only body in the solar system with liquid water on its surface.

64. Atmospheres
All the terrestrial planets and the Moon have some atmosphere.
The Moon and Mercury have very thin atmospheres while Venus has the thickest.

65. Venus at inferior conjunction

69. Effects of atmospheres
Atmospheric pressure keeps liquids from boiling
Protects the surface from solar wind and cosmic rays and, depending on composition, ultraviolet and x-ray radiation
Moderates surface temperatures

71. Discussion
How do you think an atmosphere can moderate a planet’s surface temperature?

73. As the Sun shines on the planets surface, it heats the soil and rocks
As the Sun shines on the planets surface, it heats the soil and rocks. Without an atmosphere that heat is radiated away mostly in the low-energy infrared region of the spectrum.
If the planet has an atmosphere, the heat can be transferred to the gas molecules and stored, acting as a blanket.

74. Discussion
Rank the terrestrial planets (including the Moon) in terms of their daily temperature swings from most extreme to the least extreme?

75. Surface temperatures Mercury – day: 425 C night: -175 C
Moon – day: 125 C night: -175 C
Mars – day: C night: C
Earth – day: 15 C night: C
Venus – day: 470 C night: 470 C

76. Discussion
Although Venus is closer to the Sun than Earth, its cloud cover reflects nearly 60% of the light that falls on it. The surface therefore receives less energy from the Sun that the Earth’s surface does.
So why is Venus so much hotter than Earth?

77. The greenhouse effect
Carbon dioxide (as well as water vapor and methane) absorb infrared radiation. Sunlight can pass to the surface of Venus and heat it. But the infrared radiation it emits can not escape back into space.
Earth greenhouse gases are only 1% and heat the surface by only 36 degrees.

79. Exam next Tuesday
Covers chapters 1-4 in the text + Seasons (p265) and all lecture notes including this week
4 essay questions in which you will be asked to explain concepts
Allowed one sheet of notes with writing on one side only