Lecture Slides
CHAPTER 6: Terrestrial Worlds in the Inner Solar System
Understanding Our Universe
SECOND EDITION
Stacy Palen, Laura Kay, Brad Smith, and George Blumenthal
Prepared by Lisa M. Will,
San Diego City College
Copyright © 2015, W. W. Norton & Company
Terrestrial Worlds in the Inner Solar System
 Use comparative
planetology to
understand the worlds
of the inner solar
system.
 Understand the
processes that affect
the interiors and
surfaces of terrestrial
worlds.
Comparative Planetology
 Comparative
planetology: studying
planets by comparing
them to one another.
 Terrestrial worlds:
•
•
•
•
•
Mercury
Venus
Earth
Mars
(Earth’s Moon)
Comparative Planetology: Comparison Table
Comparative Planetology: Process
 Four processes have
shaped the terrestrial
worlds:
•
•
•
•
Impact cratering
Tectonism
Volcanism
Erosion
Impacts
 Material falling from
space onto a world’s
surface will create
impact craters.
 All terrestrial worlds
experience this.
 Large impacts can
release huge amounts
of energy.
Impacts: Craters
 Venus and Earth have
relatively few craters.
 Mercury and the Moon are
covered with craters.
 Craters on Mars suggest it
had liquid water on its surface
in its past.
Impacts: Surface
 The number of craters
indicates the surface’s
age.
 More craters means
an older surface and
minimal geologic
activity.
 Tectonism and erosion
can erase craters.
Impacts: Radiometric Dating
 Rocks returned from
Moon missions give
ages through
radiometric dating.
 Almost all cratering
happened in the first
billion years of the
Solar System.
Class Question
Region A of a terrestrial world has 20 impact
craters. Region B, which has the same size as
Region A, has 5 impact craters. Which region is
likely to be older?
A. Region A
B. Region B
Interiors
 We model the Earth’s interior by
studying earthquakes.
 Earthquakes produce seismic
waves, which travel differently
through different materials.
Interiors: Earth’s Structure
Earth’s structure:
 Crust
 Mantle
 Outer Core
 Inner Core
=> Differentiation in the early Earth:
dense materials sink; low-density
materials rise.
Interiors: Moon’s Structure
 Moon formed in large collision
between Earth and Mars-sized
protoplanet. REALLY!
 The material collected to form the
Moon.
• Composition of the Moon is like that of
Earth’s crust.
Interiors: Tidal Effects
 Recall that distance affects
the strength of the
gravitational force.
 If one object is large enough
to feel different gravitational
pulls on opposite sides, it
experiences tidal stress.
Interiors: Moon’s Effect on Earth
 The Moon causes Earth to stretch => Tides!
 Earth’s oceans flow in response to the stretching of
these tidal forces.
 The behavior is complicated by Earth’s landmasses
and tidal forces due to the Sun.
Interiors: Tidal Heating
 Tides can affect the solid part of Earth.
 Results in friction, which generates heat.
 Tidal heating is one of the important factors for a
body’s internal heat.
Interiors: Tidal Heating (Cont.)
Interiors: Tidal Heating (Cont.)
Interiors: Tidal Heating (Cont.)
Interiors: Moon’s Formation
 Temperature and pressure increase
deeper into a world.
 Formation energy and radioactive
material also help to heat the
interior.
 Smaller worlds lose heat faster,
large ones more slowly.
Interiors: Earth’s Magnetic Field
 The structure of the Earth’s magnetic field resembles
that of a bar magnet.
 However, the Earth’s magnetic field is actually due to
currents flowing in its conducting outer core as it
rotates.
Interiors: Planets with Magnetic Field
 Earth and Mercury are the only terrestrial planets with
a substantial magnetic field.
 Mars has a very weak magnetic field.
 Venus has no magnetic field, likely due to its extremely
slow rotation.
Interiors: Planets with Magnetic Field (Cont.)
Interiors: Planets with Magnetic Field (Cont.)
Class Question
Which of the following layers of the Earth’s interior
should be the hottest?
A.
B.
C.
D.
Crust
Inner Core
Mantle
Outer Core
Class Question
Which of the following layers of the Earth’s interior
is composed of liquid metal?
A.
B.
C.
D.
Crust
Inner Core
Mantle
Outer Core
Class Question
Which of the following layers of the Earth’s interior
should be least dense?
A.
B.
C.
D.
Crust
Inner Core
Mantle
Outer Core
Class Question
What should be true about Earth’s internal heat?
A. It is produced by the magnetic field.
B. It would have been greater long ago when
Earth was young.
C. It currently is produced by differentiation.
Tectonism
 Tectonism is the
deformation of Earth’s
crust.
 The lithosphere (made
of the crust and upper
part of the mantle) is
broken into plates.
 Continental drift and
plate tectonics describe
the movement of those
plates.
Tectonism: Convection
 Crustal plates are moved by convection.
 Convection = rising and falling of hot/cold material.
 Earth has seven major plates and six smaller ones.
Tectonism: Convection (Cont.)
Tectonism: Convection (Cont.)
Tectonism: Plate Tectonics
 Plates can separate or collide.
 Most volcanoes and earthquakes occur along plate
boundaries, because of these motions.
Tectonism: Tectonic Disruptions
 Only Earth has its crust broken into
tectonic plates.
 All terrestrial planets have seen
some form of disruption.
 Mercury’s surface shrank after it
cooled, leaving cliffs.
Tectonism: Evidence
 Mars shows evidence of extensive
tectonism, and boasts the massive
chasm Valles Marineris.
 Venus is covered with tectonic
fractures and volcanoes.
Volcanism
 Volcanoes form
(mostly) at hot
spots and plate
boundaries.
 Friction raises the
temperature of the
rock to its melting
point.
Volcanism: Lava Forms
 Very fluid lava
forms shield
volcanoes.
 Viscous lava
forms composite
volcanoes.
Volcanism: Lava Forms (Cont.)
Volcanism: Lava Forms (Cont.)
Volcanism: Lava Forms (Cont.)
Volcanism: Lava on Moon’s Surface
 The Moon had past lava flows
which smoothed out parts
of its surface.
 Mercury also has smooth
surfaces from past volcanism,
and a few inactive volcanoes
have been identified.
Volcanism: Topographic Data
 The shield volcanoes on Mars are the largest
mountains in the Solar System.
 Venus has the greatest number of volcanoes of the
terrestrial planets.
Erosion
 Erosion is the wearing down of a world’s surface due to
mechanical action.
 Impact cratering and volcanism are forms of erosion.
 Tectonism can cause erosion.
 Wind modifies the surfaces of Earth, Venus and Mars.
Erosion: Effect of Water
 On Earth, liquid water
strongly erodes the
surface.
 Water modified the
surface of Mars in the
past, and exists today
as ice.
 Water ice also exists on
the Moon and possibly
Mercury.
Erosion: Search for Water
 The rocks on the lefthand side are on
Mars; the ones on the
right are on Earth in a
stream-bed.
 The similarity is
evidence that Mars
once had liquid water
on its surface.
Chapter Summary
 The terrestrial planets are Mercury, Venus, Earth, and
Mars.
• The Moon also shares terrestrial characteristics.
 Four major processes shape the surfaces of these
worlds:
•
•
•
•
Impact cratering
Tectonism
Volcanism
Erosion
Astronomy in Action
Tides
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AstroTour
Continental Drift
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AstroTour
Processes That Shape Planets
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AstroTour
Hot Spot Creating a Chain of Islands
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AstroTour
Tides and the Moon
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Nebraska Applet
Planetary Formation Temperatures Plot
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(Requires an active Internet connection)
Understanding Our Universe
SECOND EDITION
Stacy Palen, Laura Kay, Brad Smith, and George Blumenthal
Prepared by Lisa M. Will,
San Diego City College
This concludes the Lecture slides for
CHAPTER 6: Terrestrial
Worlds in the Inner Solar
System
wwnpag.es/uou2
Copyright © 2015, W. W. Norton & Company