1. Inner Planetary Geology II
AST 111 Lecture 17

2. Geology of the Moon The Moon is geologically dead.
Cooled so that mantle convection has stopped

3. Geology of the Moon The Moon is covered in regolith
A loose, powdery substance – why?

4. Where did it come from?
4.5 billion years ago, Earth suffered a massive collision
Ejected material formed the Moon
Composition of moon rocks similar to those found on Earth
Moon has small iron core

5. Geology of the Moon Two regions Maria Highlands Dark, smooth areas
Bright, heavily cratered

6. Geology of the Moon
Impact cratering most important geological process on the Moon
No recent volcanism or tectonics to erase them
No atmosphere to shield from them
Gravity too weak to hold onto an atmosphere
No erosion (requires wind, flowing liquid, etc.)

7. Geology of the Moon
A “spike” in impacts happened 700 million years after the Moon formed
Late Heavy Bombardment
May have been caused by migration of Jupiter and Saturn

8. Geology of the Moon Lunar maria have few craters
Formed after heavy bombardment period
Gives an estimate of duration of heavy bombardment period.

9. Geology of the Moon
Maria were created when massive impacts fractured the lithosphere. Heat
build-up from radioactive decay caused lava to flow up through cracks in the lithosphere, which flooded the impact crater and created volcanic plains.

10. Geology of the Moon Maria are dark because of iron-rich rock
They are large. Must have had very runny lava.
Near-side lithosphere is more thin
More maria on the near side

11. Geology of the Moon

12. Geology of Mercury Very similar to the Moon Geologically dead
Mercury’s craters less crowded than on the Moon
Mercury is larger
Geologically active after bombardment

13. Geology of Mercury
Mercury has cliffs (2+ miles high, hundreds of miles long)
Mercury is thought to have shrunk
Huge core, small lithosphere
Was HOT, cooled off quickly
“Crumpled” the surface
Closed volcanic vents

14. Geology of Mars Larger than the Moon and Mercury
Smaller than Venus and Earth
Geologically “dying”
Had volcanism
Had tectonics
Had water erosion
Still a few signs of activity

15. Geology of Mars
Mars is mostly rocks and dust. It’s cold and desolate.

16. Geology of Mars It’s orange because the dust contains iron
Iron rusts when exposed to atmosphere

17. Geology of Mars Northern Plains: almost no cratering
Erased by geological activity?
Ocean?
Southern Plains: lots of craters

18. Geology of Mars Large shield volcanoes Not active Tharsis Bulge
Olympus Mons: largest volcano in the solar system
Size of Arizona
Not active
Mars is small so its interior has cooled
Lithosphere is thickening

19. Geology of Mars Has some tectonic features Not many compared to Earth
Valles Marineris
Covers 1/5 of Mars’ equator
4x as deep as Grand Canyon

20. Geology of Mars Water erosion features are everywhere!
Signs of dried up lakes and riverbeds

21. Geology of Mars Liquid water would be “unstable” on Mars right now
Low temperature tries to freeze it
Low pressure tries to evaporate it
Because erosion features present:
There had to be abundant liquid
Probably water
Other liquids would freeze / evaporate

22. Geology of Mars Surface conditions must have been different
Warmer
More atmospheric pressure
Notice the impact craters in the “riverbeds”
2-3 billion years since something was flowing

23. Geology of Mars More evidence for water
Erosion of crater rims, lack of small craters
Sculpted patterns in eroded crater
Valleys often connect two lake-like bodies

24. Geology of Mars Even more evidence for water
2004, Spirit and Opportunity landed on opposite sides of Mars
Opportunity:
Meridiani Plains
Spectroscopic evidence of minerals that form in water

25. Geology of Mars Frozen water thought to reside in ice caps, soil
If near volcanic heat, could support life
Evidence for small liquid water flows

26. Geology of Venus
VENUS = HELL!

27. What are we looking at?

28. Surface of Venus Thick cloud cover won’t let us see surface
Radio waves pass through clouds and bounce off the surface

29. Geology of Venus Venus is called “Earth’s sister planet”
Similar mass, size, and interior composition
Extremely different above the surface
There is an explanation – next week

30. Conditions On Venus Sulfuric acid clouds
90x atmospheric pressure than Earth
900 oF on the surface
Soviet Venera Lander (real picture)
(Reconstructed from radar data)

31. Geology of Venus Impact craters are rare No small craters
Little erosion – craters persist
Too hot for ice or liquid flow
Slow rotation (243 days!) and hot everywhere, so little wind

32. Geology of Venus Steep Stratovolcanoes Shield volcanoes
Thick lava
Shield volcanoes
Volcanoes probably active, no observed eruptions

33. Geology of Venus Tectonically active
Surface fractured in regular patterns

34. Geology of Venus Active mantle convection
Pushes rock and lava to the surface
This is a “mantle plume” (note tectonic stress)

35. Geology of Earth
Lithospheres of Mercury, Venus, Mars are each one solid piece
Earth’s lithosphere is fractured into tectonic plates.
Fractured by mantle convection
Weaker lithosphere than other planets?

36. Geology of Earth
Earth’s features shaped primarily by plate tectonics

37. Geology of Earth Plates are fractured pieces of the lithosphere
They “float” on the solid mantle
Continents were one landmass
Fossils found on shores of different continents

38. Geology of Earth
Tectonic plate boundaries: large things and large forces
Plates can push together
Himalayas: India plate running into Eurasia plate
Plates can pull apart
Rift valleys form
Plates can slide
They don’t do it gracefully (earthquakes)