Earth and The Terrestrial Worlds

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Chapter 7

• Earth and The Terrestrial Worlds

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Principles of Comparative Planetology

• Comparative Planetology is the study of the solar
  system through examining and understanding the
  similarities and differences among the planets.
• Planetary Geology
• The study of surface features and the processes
  that create them is called geology.
• Today, we speak of planetary geology, the
  extension of geology to include all the solid
  bodies in the solar system.

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Viewing the Terrestrial Worlds

• Spacecraft have visited and photographed all of
  the terrestrial worlds. Some have even been
  landed on!
• Because surface geology depends largely on a
  planets interior, we must first look inside the
  terrestrial worlds.

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Global views and surface close-ups
Venus surface- atmosphere is not shown. Surface
mapped from Megellan spacecraft radar data
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• Surface Views of some of the terrestrial worlds.
• Venus, the Moon and Mars have all been landed on
  successfully by spacecraft from Earth.

Venus Venera Missions (1961-1983)
Apollo Lunar Missions (1969-1972)
Links Mars Exploration Rover Mission The
Mission Mars Pathfinder
Mars Pathfinder Mission (1996-1997)
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Inside the Terrestrial Worlds

• When subjected to sustained stress over millions
  to billions of years, rocky material slowly
  deforms and flows.
• Rock acts more like Silly PuddyTM , which
  stretches when you pull it slowly but breaks if
  you pull it sharply.
• The rocky terrestrial worlds became spherical
  because of rocks ability to flow.
• When objects exceed about 500 km in diameter,
  gravity can overcome the strength of solid rock
  and make a world spherical

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• Gravity also gives the terrestrial worlds similar
  internal structures.
• Distinct layers are formed by differentiation.
• Differentiation is the process by which gravity
  separates materials according to their density.
• This resulted in three layers of differing
  composition within each terrestrial planet.
• Core
• Mantle
• Crust

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• Lithosphere Outer layer of relatively rigid rock
  that encompasses the crust and the uppermost
  mantle.

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• Heat flows from the hot interior to the cool
  exterior by conduction and convection.
• Condution Heat transfer as a result of direct
  contact.
• Convection Heat transfer by means of hot
  material expanding and rising and cool material
  contracting and sinking.
• A small region of rising and falling material is
  called a convection cell.

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Shaping Planetary Surfaces
There are four main geological processes

• Impact Cratering the excavation of bowl-shaped
  depressions (impact craters) by asteroids or
  comets striking a planets surface.
• Volcanism the eruption of molten rock, or lava,
  from a planets interior onto its surface.
• Tectonics the disruption of a planets surface
  by internal stresses.
• Erosion the wearing down or building up of
  geological features by wind, water, ice, and
  other phenomena of planetary weather.

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Impact Process
Ejecta
Impact
Ejecta Blanket
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Cratering
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Volcanism
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(Mount St. Helens)

• c) Sticky lava makes steep-sloped
  stratovolcanoes.

Picture by US Geological Survey scientist, Austin
Post, on May 18, 1980.
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Tectonic Forces at work.
Convection Cells
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Comparing Planetary Atmospheres
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Atmospheric Structure
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Visible Light Warming the Surface and Coloring
the Sky
Atmospheric gases scatter blue light more than
they scatter red light. Longer wavelength red
light is more penetrating
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Infrared Light the Greenhouse Effect, and the
Tropsosphere

• The Troposphere becomes warmer than it would if
  it had no greenhouse gases.
• Greenhouse gases include
• CO2
• Water Vapor

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The Greenhouse Effect
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Temperatures of the Terrestrial Worlds
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• Ultraviolet light is absorbed in the
  Stratosphere.
• X-Rays are absorbed in the Thermosphere and
  Exosphere.

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The Magnetosphere

• The Magnetosphere blocks the Solar Wind
• This produces two regions where the charged
  particles get trapped Van Allen Belts.

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• The interaction of the charged particles from the
  solar wind near the poles, produces the
• Aurora Borealis (Northern Lights)
• Aurora Australis (Southern Lights)

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Aurora Borealis Norhern Lights
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Atmospheric Origins and Evolution

• Outgassing from Volcanic activity was most
  responsible for producing the earths early
  atmosphere. (Volcanoes give off H2O, CO2, N2, and
  sulfur compounds.
• As life developed, it too influenced the
  atmosphere of the Earth, allowing it to become
  what it is today. (e.g. plants give off O2 and
  consume CO2)

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Many gases can escape from the planet if their
thermal speed is greater than the escape speed of
the planet.
Five Major Processes By Which Atmospheres Lose
Gas.
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A Tour of the Terrestrial Worlds
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The Moon 1,738-km radius, 1.0AU from the Sun
Astronaut explores a small crater
An ancient lava river
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Mercury (2,440-km radius, 0.39AU from the Sun)
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Dust Storm over northern ice cap, Mars
Global Surveyor
Polar Ice Cap (Mars) Viking Orbiter
Edge of polar ice cap showing layers of ice and
dust.
Mars (3,397-km radius, 1.52 AU from the Sun)
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Cratering, Volcanism and Tectonics
Valles Marineris
Heavy cratering in Southern Hemisphere (Mars)
Olympus Mons largest shield volcano in the
solar system
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Martian outflow channels and flood planes
Ancient River beds
Outflow channels indicate catastrophic flooding
Water eroded crater
Gullies on a crater wall formed by water flows?
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Venus (6,051-km radius, 0.72 AU from Sun)
Shield Volcanoes are common
Impact craters on Venus are rare
Fractured and twisted crust
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Earth (6, 378 km radius, 1.0 AU from the Sun)
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Time-Line of Geologic Activity
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End of Section