Lecture 10: Comparative Geology of the Terrestrial Planets

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Lecture 10 Comparative Geology of the
Terrestrial Planets
Olympus Mons (Mars) Volcanic caldera

• Claire Max
• May 7, 2007
• Astro 18 Planets and Planetary Systems
• UC Santa Cruz

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Practicalities

• There WILL be labs this week (Wed, Thurs)
• Work on projects
• Groups get together (decide which day)
• ISB 356 so there will be wireless internet
• Bring your laptops if possible

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Comparative Geology of the Terrestrial Planets
Outline

• Planetary interiors
• Four processes that shape planetary surfaces
• Cratering
• Volcanism
• Tectonics
• Erosion

Please remind me to take a break at 245 pm!
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The Main Points

• A few basic processes mold surfaces and interiors
  of terrestrial planets
• All terrestrial planets were once heavily
  cratered, but craters have since been erased on
  some
• Planet size influences volcanism, tectonics
  atmosphere influences erosion
• General features should be same in other solar
  systems, not just our own

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How can we make sense of the terrestrial planets?

• Look for the common basic processes that make
  them look the way they do

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Interiors of the terrestrial planets

• Differentiation
• molten early in histories
• iron, nickel sank to core
• silicates (rocky material) came to rest above
  core mantle floats on core
• lowest-density silicates formed thin crust
• Can also characterize in terms of strength
• lithosphere rigid
• asthenosphere deforms and flows more easily
• Note rock can flow!

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Variety in planet interiors

• Higher internal temperature rocks softer
  thinner lithosphere
• Thin lithosphere enables volcanism, continental
  drift

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Seismic Waves

• Vibrations that travel through Earths interior
  tell us what Earth is like on the inside
• Source earthquakes!
• Detectors seismographs

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Seismic waves tell us about planetary interiors

• Measure travel paths of seismic waves from
  earthquakes
• Combine with physical models of materials
• Has been done on Earth (a lot), Moon

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Why do some planetary interiors create magnetic
fields?
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Sources of Magnetic Fields
Current

• Motions of charged particles are what create
  magnetic fields

Battery
Current
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Sources of Planetary Magnetic Fields

• A world can have a magnetic field if charged
  particles are moving inside
• 3 requirements
• Molten interior
• Convection
• Moderately rapid rotation

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Planets with molten cores have magnetic fields

• Dynamo process
• Convection within molten core
• Convection rotation causes electric current
• Electric current makes magnetic field (as in
  electromagnet)

• Earth molten core, fast rotation ? strong
  magnetic field
• Venus molten core, slow rotation (or small
  convection) ? no field
• Mars and Moon much smaller, cooled faster, solid
  core ? no field
• Mercury has magnetic field ? big metallic core
  molten??

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What have we learned?

• What are terrestrial planets like on the inside?
• Core, mantle, crust structure
• Denser material is found deeper inside
• What causes geological activity?
• Interior heat drives geological activity
• Radioactive decay is currently main heat source
• Why do some planetary interiors create magnetic
  fields?
• Requires motion of charged particles inside
  planet
• Core must be molten

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Differentiation

• Gravity pulls high-density material to center
• Lower-density material rises to surface
• Material ends up separated by density

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ConcepTest

• What is necessary for differentiation to occur
  in a planet?
• a) It must have metal and rock in it
• b) It must be a mix of materials of different
  density
• c) Material inside must be able to flow
• d) All of the above
• e) b and c

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ConcepTest

• What is necessary for differentiation to occur
  in a planet?
• a) It must have metal and rock in it
• b) It must be a mix of materials of different
  density
• c) Material inside must be able to flow
• d) All of the above
• e) b and c

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Three processes that heat planet interiors
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How do planet interiors cool off?

• Size is critical factor
• Larger planets stay hot longer
• Smaller planets cool quicker
• Why?

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Smaller planets cool more quickly

• Heat content depends on volume
• Loss of heat through radiation depends on surface
  area
• Time to cool depends on surface area divided by
  volume

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Size influences internal temperature

• Earth and Venus are biggest, interiors are
  hottest, lithospheres are thinnest
• Another way to see this larger planets have more
  mantle material to provide insulation, slow
  cooling processes

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ConcepTest

• A small planetary object, like the Moon, is most
  likely to be
• a) solid on the inside, with little magnetic
  field
• b) liquid in the inside, with little magnetic
  field
• c) solid on the inside, with a strong magnetic
  field
• d) liquid on the inside, with a strong magnetic
  field

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Four processes that shape planetary surfaces

• Impact cratering
• excavation of bowl-shaped craters when asteroids
  or comets or small meteorites hit a planets
  surface
• Volcanism
• eruption of molten rock (lava) from planets
  interior onto its surface
• Tectonics
• disruption of planets surface by internal
  stresses
• Erosion
• wearing down or building up of geological
  features by wind, water, ice, other weather
  effects

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Role of planetary size
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Role of distance from Sun
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Role of planetary rotation
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Planets formation properties influence geology
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Impact processes
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Impact cratering on Earth

• Manacouagan Crater Canada

Barringer Meteor Crater Arizona
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Craters on Moon, Mars
Maria impact basins filled in with lava
Impacts into icy ground may produce muddy ejecta
Highlands ancient and heavily cratered
Mars craters
Moon craters
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Craters on Venus, Mercury
Mercury
Venus
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How Magellan spacecraft used radar to map surface
of Venus

• http//www.classzone.com/books/earth_science/terc/
  content/visualizations/es2702/es2702page01.cfm?cha
  pter_novisualization

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Flow chart for cratering
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Volcanism

• Lowest-viscosity lava flat lava plains
• Maria on the Moon
• Shield volcanoes medium viscosity lava
• lava is still runny
• produces volcanoes with shallow slopes (lt10 deg)
• Composite or strato-volcanoes
• lava has high viscosity (goopy)
• makes steep sloped volcanoes (gt30 deg)

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Shield volcanoes on Earth, Venus, Mars, Io
Mars Olympus Mons
Earth Mauna Loa, Hawaii
Io Ra Patera
Venus Sif Mons
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Caldera when vent of volcano collapses
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Calderas on Earth, Venus, Mars
Venus Sacajawea
Earth Galapagos Islands
Mars Olympus Mons
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Cinder cones on Earth, Moon, Mars
Moon (2)
Earth Puu Oo
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Volcanism flow chart
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Tectonics motion of surface features due to
internal processes

• tectonics_convect_of_mantle.htm

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Tectonics on Earth, Venus. Mars
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Evidence that Mercury shrank!
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Tectonics stretch graben
Graben on Ganymede
Graben on Mars
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Earth is only planet in our Solar System that has
active plate tectonics today

• Crust is broken up into plates that move
• Evidence matching coastlines on different
  continents

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Plate boundaries and earthquake frequency on Earth
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More evidence for continental drift

• Matching mountain ranges across oceans

300 million years ago
Today
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More evidence for continental drift

• Distribution of fossils such as Mesosaurus

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How is Earths surface shaped by plate tectonics?
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Seafloor Recycling

• Seafloor is recycled through a process known as
  subduction

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Subduction at plate boundary
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Processes that built North America
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Tectonics flow chart
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Volcanic and tectonic histories
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Erosion rockfalls
Earth Grand Canyon
Mars at bottom of Olympus Mons
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Erosion rockfalls
Mars see individual boulders fall
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Erosion slumps
Slump on Mars
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Slumps on Earth are usually due to liquid water

• Is this indirect evidence for liquid water on
  Mars?

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Erosion debris flows on Earth and Mars
Mars wet debris flow
Earth San Jacinto Mountains, CA
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Erosion water can carve canyons
Earth Grand Canyon
Mars Valles Marineris
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Erosion flood channels on Earth, Mars
Washington State channeled scablands Giant
flood 13,000 yrs ago
Mars Kasei Valles flood channel
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Erosion desert pavement on Earth, Venus, Mars
Earth Death Valley
Cartoon
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Erosion transverse sand dunes
Earth Namib desert
Mars Hebes Casma dunes
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Dunes on Saturns moon Titan
Titan dunes (radar image)
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Erosion flow chart
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ConcepTest

• Consider the four geological processes
  cratering, volcanism, tectonics, erosion.
• Which two do you think are most closely connected
  with each other?
• Give several ways in which these processes are
  connected

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What have we learned?

• How do we know that Earths surface is in motion?
• Measurements of plate motion confirm idea of
  continental drift
• How is Earths surface shaped by plate tectonics?
• Plate tectonics responsible for subduction,
  seafloor spreading, mountains, rifts, and
  earthquakes
• Was Earths geology destined from birth?
• Many of Earths features determined by size,
  distance from Sun, and rotation rate

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The Main Points

• A few basic processes mold surfaces and interiors
  of terrestrial planets
• All terrestrial planets were once heavily
  cratered, but craters have since been erased on
  some
• Planet size influences volcanism, tectonics
  atmosphere influences erosion
• General features should be same in other solar
  systems, not just our own

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Cassini Spacecraft flies by Titan on Saturday May
12th

• See it on the web or on NASA TV
• http//saturn.jpl.nasa.gov/news/events/titan200705
  12/index.cfm