Transcript Earth and the Terrestrial Worlds

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:
• 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
• 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
Venus’ surface- atmosphere is not
shown. Surface mapped from
Megellan spacecraft radar data
• Surface Views of some
of the terrestrial worlds.
• Venus, the Moon and
Mars have all been
landed on successfully
by spacecraft from Earth.
Links
Venus – Venera Missions (1961-1983)
Apollo Lunar Missions (1969-1972)
Mars Exploration Rover
Mission: The Mission
Mars Pathfinder
Mars Pathfinder Mission (1996-1997)
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
There are four main geological processes
• Impact Cratering: the excavation of bowlshaped 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
Ejecta
Ejecta Blanket
Cratering
Volcanism
(Mount St. Helens)
c) “Sticky” lava makes steepsloped stratovolcanoes.
Picture by US Geological
Survey scientist, Austin
Post, on May 18, 1980.
Tectonic Forces
at work.
Convection
Cells
Comparing Planetary Atmospheres
Atmospheric Structure
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
• The Troposphere becomes warmer than it
would if it had no greenhouse gases.
• Greenhouse gases include:
– CO2
– Water Vapor
The Greenhouse Effect
Temperatures of the Terrestrial Worlds
• Ultraviolet light is absorbed in the
Stratosphere.
• X-Rays are absorbed in the
Thermosphere and Exosphere.
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)
Aurora Borealis – Norhern Lights
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.
A Tour of the Terrestrial
Worlds
The Moon 1,738-km radius, 1.0AU from the Sun
Astronaut explores a small crater
An ancient lava river
Mercury
(2,440-km radius,
0.39AU from the Sun)
Polar Ice Cap (Mars)
Viking Orbiter
Dust Storm over northern ice cap,
Mars Global Surveyor
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
(Mars)
Olympus Mons:
– largest shield
volcano in the
solar system
Ancient
River
beds
Water eroded
crater
Martian outflow channels and flood planes
Outflow channels indicate
catastrophic flooding
Gullies on a
crater wall
formed by
water flows?
Venus (6,051-km radius, 0.72 AU from Sun)
Impact
craters
on
Venus
are rare
Fractured
and
twisted
crust
Shield Volcanoes
are common
Earth (6, 378 km
radius, 1.0 AU
from the Sun)
Time-Line of Geologic Activity
End of Section