1. Exam 2: Wednesday, March 30 Review Session: Tuesday 3/29, 7:00-9:00 Swain West 007

2. The Terrestrial Planets
Mercury
Venus
Earth
Mars

3. Mars

4. Early in their existence, the Terrestrial planets and the large moons had an extended period when they were mostly molten.
The heating that led to this condition was caused by impacts, where the kinetic energy of the impacting material was converted to thermal energy.
Today, the interiors of planets are heated mainly by radioactive decay.

5. interior structure of the planet, surface features, atmosphere,
The heating to a molten state, and subsequent cooling, had important repercussions for:
interior structure of the planet,
surface features,
atmosphere,
magnetic fields,
presence/absence of water.

6. Differentiation – the process by which gravity separates materials according to their densities
Denser materials sink, less dense material “float” towards top

7. Differentiation during the molten phase resulted in the formation of three distinct density zones within each terrestrial world:
Core - contains metals (e.g., iron, nickel)
Mantle – intermediate layer with rocky material
(sometimes partially semi-molten)
Crust – lowest-density rocks (surface)

8. Terrestrial planets have metallic cores (which may or may not be molten) & rocky mantles
Earth (solid inner, molten outer core)
Mercury (solid core)
Earth’s interior structure

9. Differentiated Jovian moons have rocky cores & icy mantlesIo
Europa
Ganymeade
Callisto

10. The Lithosphere…
Layer of rigid rock (crust plus upper mantle) that floats on softer (mantle) rock below
While interior rock is mostly solid, at high pressures and stresses can cause rock to deform and flow (think of silly putty)
This is why we have spherical planets/moons

11. The interiors of the terrestrial planets slowly cool as their heat escapes.
Interior cooling gradually makes the lithosphere thicker and moves molten rocks deeper.
Larger planets take longer to cool, and thus:
1) retain molten cores longer
2) have thinner (weaker) lithospheres

12. Lithospheres of the Terrestrial planets and the Earth’s Moon
The stronger (thicker) the lithosphere, the less geological activity the planet exhibits.
Planets with cooler interiors have thicker lithospheres.
Lithospheres of the Terrestrial planets
and the Earth’s Moon

13. Stresses in the lithosphere lead to “geological activity” (e. g
Stresses in the lithosphere lead to “geological activity” (e.g., volcanoes, mountains, earthquakes, rifts, …) and, through out-gassing, leads to the formation and maintenance of atmospheres.
Cooling of planetary interiors (energy transported from the planetary interior to the surface) creates these stresses

14. Convection in the Mantle
Convection - the transfer of thermal energy in which hot material expands and rises while cooler material contracts and falls (e.g., boiling water).
Decreasing Temperature
Convection is the main cooling process for planets with warm interiors.

15. Larger planets stay hot longer.
Earth and Venus (larger) have continued to cool over the lifetime of the solar system  thin lithosphere, lots of geological activity
Mercury, Mars and Moon (smaller) have cooled earlier  thicker lithospheres, little to no geological activity

17. Side effect of hot interiors - global planetary magnetic fields
Requirements:
Interior region of electrically conducting fluid (e.g., molten iron)
Convection in this fluid layer
“rapid” rotation

18. Earth fits requirements
Venus rotates too slowly
Mercury, Mars & the Moon lack molten metallic cores
Sun has strong field

19. Planetary Surfaces 4 major processes affect planetary surfaces:
Impact cratering – from collisions with asteroids and comets
Volcanism – eruption of molten rocks
Tectonics – disruption of a planet's surface by internal stresses
Erosion – wearing down or building up geological feature by wind, water, ice, etc.

20. Impact Cratering: The most common geological process shaping the surfaces of rigid objects in the solar system (Terrestrial planets, moon, asteroids)

21. Volcanism
Volcanoes help erase impact craters

22. Volcanic outgassing: source of atmospheres and water

23. Erosion: the breakdown and transport of rocks and soil by an atmosphere.
Wind, rain, rivers, glaciers contribute to erosion.
Erosion can build new formations: sand dunes, river deltas, deep valleys).
Erosion is significant only on planets with substantial atmospheres.

24. Tectonics: the action of internal forces and stresses on the lithosphere leading to the creation of surface features & geological activity.
Tectonics can only occur on planets with convection in the mantle (Earth & Venus today, some Jovian moons)

25. Tectonics…
raises mountains
creates huge valleys (rifts) and cliffs
creates new crust
moves large segments of the lithosphere (plate tectonics)

26. Tectonic plates

28. divergent plate boundary (plates move away from each other).
Atlantic Ocean
Great Rift Valley in Africa
Valles Marineris (Mars)

29. Portion of Valles Marineris on Mars – created by tectonic stresses

30. convergent plate boundary with subduction : plates move towards each other & one slides beneath the other.
Nazca plate being subducted under the South American plate to form the Andes Mountain Chain.
Island arc system

31. convergent plate boundary without subduction : plates move towards each other and compress.
Formation of Himalayas.

32. Plates sliding past each other (transform zones): earthquakes, valleys, mountain building

33. Half of the world’s volcanoes surround the Pacific plate
Tectonic plates

34. Tectonic plates Convergent plates: No subduction
Convergent plates: Subduction
Transform fault
Tectonic plates
Spreading plates: rift valley
Divergent plates: oceanic ridge

35. Tectonic plates & Japanese earthquake

36. Tectonic plates & Japanese earthquake

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

38. erosion
cratering
vulcanism
tectonics

39. Group Activity
What are things that Venus and Mars have in common?
In what ways do they differ?
On which planet would you expect to find taller mountains?
Ice caps?
On which planet would you expect the sun’s radiation to be more dangerous to life?
Would you like to visit either of them?
Do you expect to be able to visit either of them during your lifetime? If so, which one?

40. Terrestrial planets are mostly made of rocky materials (with some metals) that can deform and flow.
Likewise, the larger moons of the Jovian planets are made largely of icy materials (with some rocks and metals) that can deform and flow.
The ability to deform and flow leads every object exceeding approximately 500 km in diameter to become spherical under the influence of gravity.