Announcements

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Announcements

• 25 people have still not joined the class on
  Astronomy Place. You can not get credit until
  you join the class. Once you join, all your
  previous submissions will show up in my
  gradebook.
• Planet Assignment 4, due Monday March 1,
• Part 1 Astronomy Place tutorial Shaping
  Planetary Surfaces
• Part 2 Angel Planet Assignment 4

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Example of a proto-Planetary Disk
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Objectives

• Describe the significance of bombardment in the
  early solar system.
• Compare and contrast the structure evolution of
  the terrestrial planets.
• Describe the differentiation into core, mantle
  crust.
• Describe the heating and cooling processes in
  planetary interiors. Describe the importance of
  planetary size on its evolution.

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Two Types of Planets
Terrestrial small rocky, iron inner
Jovian large H, He, ices outer
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When Planets Form - Bombardment Differentiation

• Bombardment of planet as it forms, HEATS and
  melts its surface
• Molten iron and other heavy elements sink toward
  the center
• Falling iron converts gravitational potential
  energy to kinetic energy - HEAT

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Inside the Terrestrial Worlds

• After they have formed, the molten planets
  differentiate into three zones
• core - made of metals
• mantle - made of dense rock
• crust - made of less dense rock
• Lithosphere - the rigid, outer layer of crust
  part of the mantle which does not deform easily

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Inside the Terrestrial Worlds
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Heating the Planets

• Planetary interiors heat up through
• accretion
• differentiation
• radioactivity

Supplies all the heat at the beginning
Supplies heat throughout the planets life
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(No Transcript)
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Cooling the Planets

• Planets Cool by Radiating Heat to Space from
  their Surface
• Heat is Transported from the Interior to the
  Surface by
• conduction - atoms molecules moving hitting
  other atoms molecules
• convection - macroscopic flows hot material
  rising cool material sinking

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Convection
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Cooling Terrestrial Planets
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Role of Planetary SIZE

• Larger planets heat more
• More iron to flow to center
• More radioactive elements to split
• Larger planets cool slower
• Extra layers provide extra insulation

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Role of Planetary Size

• Heating proportional to Volume R3
• Cooling proportional to Surface Area R2
• Heating/Cooling Volume/Area R Size
• Smaller Planets Cool Faster Heat Less(by
  impacts and splitting of radioactive nuclei)-
  Thicker rigid Lithosphere - Less volcanism
  Tectonic Activity

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Inside the Terrestrial Worlds
active geology
inactive geology
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How do we Know about the Interior of Earth

• Earthquakes make waves
• Waves travel through Earth, the higher the
  density the faster the waves travel
• Two types of waves
• Back forth
• Side to side

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Shaping Planetary Surfaces

• Major geological processes that shape planetary
  surfaces
• impact cratering excavation of surface by
  asteroids or comets striking the planet
• volcanism eruption of lava from interior
• tectonics disruption of lithosphere by internal
  stresses
• erosion wearing down by wind, water, ice

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Counting Craters to find Surface Age

• Cratering rate decreased as Solar Systems aged.
• The older the surface, the more craters are
  present.

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Impact Craters - Mars
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Volcanism - Mars Olympus Mons
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Olympus Mons
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Volcanism - Venus
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Plate Tectonics
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History of Plate Tectonics

• South America and Africa fit together like a
  jig-saw puzzle, with matching geological
  formations and fossils
• New Idea (Wegner 1912)Continental Drift
• Rejected by Geologists
• Counter to established ideas
• Lack of overwhelming evidence
• No mechanism to drive motions

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Evidence
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Evidence
Mid-Atlantic Rift in Iceland Division
between North American European Plates
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Mechanism - Mantle Convection
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(No Transcript)
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Earths Plates
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Earths Plate Motion
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Valles Marinares - Mars
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Erosion
Mars Evidence for water in past
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Erosion
Wind
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Summary