1. Lecture 23

2. Movie Night 2
Monday, April 19
SW119 from 7:00~9:30

3. How do surface building processes apply to the Terrestrial Planets?
Vulcanism Impact cratering Erosion Tectonics

4. erosion
cratering
vulcanism
tectonics

5. Small rocky planets Cold, solid interiors (Moon, Mercury)‏
Tectonic & volcanic activity only during first billion years
Many ancient craters
Little outgassing
Atmospheres lost due to weak gravity
No erosion
(Moon, Mercury)‏

6. Mercury
Geologically dead
Vulcanism when young (small lava plains, smaller crater density than lunar highlands)‏
Days / Nights last 3 months – very hot / cold

7. Mercury
Tectonics when young
Very high cliffs extending for hundreds of kilometers, formed as folds as planet cooled and contracted

8. Moon Highlands (light colored areas): heavily cratered
about four billion years old

9. giant impact basins flooded with lava
Mare
Dark colored areas:
giant impact basins flooded with lava
lightly cratered
about billion years old (younger than highlands)‏

10. (Earth, Venus)‏ Large rocky planets Warm, convecting interiors
Ongoing tectonic & volcanic activity
Most ancient craters erased
Considerable outgassing
Atmospheres retained
Erosion exists

11. Venus
Fully cloud covered – surface not visible

12. Surface features on Venus have been investigated using radar from orbiting spacecraft

13. young surface
mostly gentle rolling plains.

14. evidence of volcanism.

15. Erosion
&
tectonics

16. few impact craters

17. tectonic activity
(folded grooves shown here)

18. Mars
Marsrovers.jpl.nasa.gov

19. erosion
cratering
vulcanism
tectonics

20. heavily cratered southern hemisphere
fewer craters in
northern hemisphere
heavily cratered southern hemisphere

21. giant volcanoes

22. Covers area the size of Arizona
Olympus Mons
Covers area the size of Arizona

23. dry stream beds, once had running water

24. Considerable evidence of water flows – younger terrain

25. heavily cratered southern hemisphere
Older terrain

26. Tectonics & erosion

27. Erosion around edge of Olympus Mons

28. part of surface young, part old
Conclusion:
part of surface young, part old

29. Summary: Surface Properties

30. Cratered terrain ubiquitous in the solar system
cratering due to planetesimals left over from formation of solar system
smallest planets (Moon, Mercury) heavily cratered
middle sized planet (Mars) has both heavily cratered and also relatively uncratered regions and extinct volcanos
largest planets (Venus, Earth) have few craters and active volcanos

31. Why?
More impact craters implies an older surface
Rate of cratering declined rapidly after planet formation
Many craters remain where there is no tectonic or volcanic activity

32. Why do some planets have old surfaces and some young surfaces?
The level of
tectonic and volcanic activity

33. Thickness of lithosphere controls extent of volcanic activity.
Thin lithosphere -> hot rocks from interior break through surface
Thick lithosphere -> hot rocks from interior can't break through surface.