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Chapter 7. Earth and The Terrestrial Worlds. 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:

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Chapter 7

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chapter 7

Chapter 7

Earth and The Terrestrial Worlds

principles of comparative planetology
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.
viewing the terrestrial worlds
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 planet’s interior, we must first look inside the terrestrial worlds.
global views and surface close ups
Global views and surface close-ups

Venus’ surface- atmosphere is not shown. Surface mapped from Megellan spacecraft radar data


Venus – Venera Missions (1961-1983)

  • Surface Views of some of the terrestrial worlds.
  • Venus, the Moon and Mars have all been landed on successfully by spacecraft from Earth.


Mars Exploration Rover Mission: The Mission

Mars Pathfinder

Apollo Lunar Missions (1969-1972)

Mars Pathfinder Mission (1996-1997)

inside the terrestrial worlds
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 rock’s ability to flow.
  • When objects exceed about 500 km in diameter, gravity can overcome the strength of solid rock and make a world spherical
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
Lithosphere: Outer layer of relatively rigid rock that encompasses the crust and the uppermost mantle.
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.
shaping planetary surfaces
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 planet’s surface.
  • Volcanism:the eruption of molten rock, or lava, from a planet’s interior onto it’s surface.
  • Tectonics:the disruption of a planet’s surface by internal stresses.
  • Erosion:the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather.
impact process
Impact Process



Ejecta Blanket


(Mount St. Helens)

c) “Sticky” lava makes steep-sloped stratovolcanoes.

Picture by US Geological Survey scientist, Austin Post, on May 18, 1980.


Tectonic Forces at work.

Convection Cells


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

infrared light the greenhouse effect and the tropsosphere
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
Ultraviolet light is absorbed in the Stratosphere.
  • X-Rays are absorbed in the Thermosphere and Exosphere.
the magnetosphere
The Magnetosphere
  • The Magnetosphere blocks the Solar Wind
  • This produces two regions where the charged particles get trapped – Van Allen Belts.
The interaction of the charged particles from the solar wind near the poles, produces the:
    • Aurora Borealis (Northern Lights)
    • Aurora Australis (Southern Lights)
atmospheric origins and evolution
Atmospheric Origins and Evolution
  • Outgassing from Volcanic activity was most responsible for producing the earth’s 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)
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.

the moon 1 738 km radius 1 0au from the sun
The Moon 1,738-km radius, 1.0AU from the Sun

Astronaut explores a small crater

An ancient lava river


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)


Cratering, Volcanism and Tectonics

Valles Marineris

Heavy cratering in Southern Hemisphere


Olympus Mons: – largest shield volcano in the solar system


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?


Venus (6,051-km radius, 0.72 AU from Sun)

Shield Volcanoes are common

Impact craters on Venus are rare

Fractured and twisted crust