Neil F. Comins • William J. Kaufmann III
Discovering the Universe
Eighth Edition
CHAPTER 7
The Other Terrestrial Planets
WHAT DO YOU THINK?
1.
2.
3.
Why are Venus (too HOT), Mars (too
COLD) and Earth (just right!) so different
in their atmospheres?
Could Mars have supported life long
ago? How do we know?
Is life known to exist on Mars today?
In this chapter you will discover…

Mercury, a Sun-scorched planet with a heavily
cratered surface and a substantial iron core

Venus, perpetually shrouded in thick, poisonous
clouds and mostly covered by gently rolling hills

Mars, a red, dusty planet that once had running
water on its surface and may still have liquid
water underground

The role of Carbon Dioxide as a insulator for
Planetary climates.
Essay Questions
Describe the atmospheres of Venus,
Earth, and Mars. Why are these three
atmospheres so different?
 What is the greenhouse effect? Which
planets experience this phenomena?
 What does the Martian surface tell us
about the planet's history, and future?

Mercury
Mercury’s Impact History
Huge impact craters as well as thousands of
smaller ones…
Mercury’s Impact History
Very Similar features on our Moon
Moon
Mercury
Mercury’s plains
Very Similar features on our Moon
Mercury’s plains
History told by craters!
Mercury’s core
Mercury’s core: A Hypothesis
Mercury’s core: A Hypothesis
Mercury’s core: A Hypothesis
News from Mercury
NASA’s Messenger Mission now
mapping Mercury’s Surface
http://www.nasa.gov/mission_pages/messenger/main/index.html
Latest Photos of Mercury
Latest Photos of Mercury
Why Explore Mercury?

Learning about Earth from other planets…
Core
 Magnetic Field
 Role of Solar Energy Exposure
 Planetary Models


NASA’s view
Venus in UV light
Venus mapped with Radar
The surface of Venus
Venus’ surface
Venera Probes from 1970’s survived for
minutes…
Venus’ surface
Venera Probes from 1970’s survived for
minutes…
Does Venus have plate
tectonics?
•
Earth’s major geological features can be
attributed to plate tectonics, which
gradually remakes our surface.
•
Venus does not appear to have plate
tectonics, but its entire surface seems to
have been “repaved” 750 million years
ago.
Why is Venus so hot?
Venus’ Atmosphere
•What is it made of?
•How does it change in height?
•How does it circulate?
Atmosphere of Venus

Venus has a very
thick carbon
dioxide
atmosphere with a
surface pressure
90 times that of
Earth.
Atmosphere of Venus

Reflective clouds
contain droplets of
sulfuric acid.

The upper
atmosphere has
fast winds that
remain
unexplained.
Venus’ Atmosphere
Venus’ Atmosphere
Sun’s UV light disassociates
H20 at this height!
Water condenses into clouds,
allowing for rain around 0 C
Greenhouse Effect on Venus

Thick carbon
dioxide
atmosphere
produces an
extremely strong
greenhouse effect.

Earth escapes this
fate because most
of its carbon and
water are in rocks
and oceans.
Why is Venus so hot?
The greenhouse effect on Venus keeps its
surface temperature at 470°C.
But why is the greenhouse effect on Venus
so much stronger than on Earth?
Explaining Venus’ Atmosphere
•Lots of Volcanoes
•CO2, H2S04 are outgassed
•CO2 traps infrared heat from Sun
•Atmosphere heats up
•Water can’t condense => No Rain!
Runaway Greenhouse Effect
More evaporation,
stronger greenhouse effect
Greater heat,
more evaporation

The runaway greenhouse effect would account
for why Venus has so little water.
Thought Question
What is the main reason why Venus is hotter
than Earth?
A.
B.
C.
D.
E.
Venus is closer to the Sun than Earth.
Venus is more reflective than Earth.
Venus is less reflective than Earth.
The greenhouse effect is much stronger on Venus
than on Earth.
Human activity has led to declining temperatures on
Earth.
Thought Question
What is the main reason why Venus is hotter
than Earth?
A.
B.
C.
D.
E.
Venus is closer to the Sun than Earth.
Venus is more reflective than Earth.
Venus is less reflective than Earth.
The greenhouse effect is much stronger on
Venus than on Earth.
Human activity has led to declining temperatures on
Earth.
Earth as a Living Planet
Our goals for learning:
 What unique features on Earth are
important for human life?
 How is human activity changing our
planet?
 What makes a planet habitable?
What processes shape
Terrestrial Planet surfaces?
Geological Processes

Impact cratering
—

Volcanism
—

Eruption of molten rock onto surface
Tectonics
—

Impacts by asteroids or comets
Disruption of a planet’s surface by internal
stresses
Erosion
—
Surface changes made by wind, water, or
ice
What unique features of Earth
are important for life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Earth’s distance from the
Climate stability
Sun and moderate
greenhouse effect make
liquid water possible.
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
PHOTOSYNTHESIS
(plant life) is required to
Climate stability
make high concentrations
of O2, which produces the
protective layer of O3.
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
Plate tectonics are
an important step
in the carbon
dioxide cycle.
Continental Motion

Motion of continents can be measured with
GPS
Continental Motion

Idea of
continental drift
was inspired by
puzzle-like fit of
continents

Mantle material
erupts where
seafloor
spreads
Seafloor Recycling

Seafloor is recycled through a process
known as subduction
Carbon Dioxide Cycle
1.
Atmospheric CO2
dissolves in
rainwater.
2.
Rain erodes
minerals that flow
into the ocean.
3.
Minerals combine
with carbon to
make rocks on
ocean floor.
Carbon Dioxide Cycle
4.
Subduction carries
carbonate rocks
down into the
mantle.
5.
Rock melts in
mantle and
outgases CO2
back into
atmosphere
through volcanoes.
How does Earth’s atmosphere
affect the planet ?
Which Molecules are Greenhouse Gases?
Radiation Protection
All X-ray light is
absorbed very high in
the atmosphere.
 Ultraviolet light is
absorbed by ozone
(O3).

The Greenhouse Effect on
Earth
The Greenhouse Effect
Which Molecules are Greenhouse Gases?
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability The CO2 cycle acts like a
thermostat for Earth’s
temperature.
Mars
Schiaparelli’s “Canals”
More illusions:
Pyramids
Happy Faces!
A Martian Sunset…
Mars vs. Earth
50% Earth’s radius, 10% Earth’s mass
 1.5 AU from the Sun
 Axis tilt about the same as Earth
 Similar rotation period (25 hours/”day”)
 Thin CO2 atmosphere: little greenhouse
effect

=>Main difference: Mars is SMALLER
Seasons on Mars

Seasons on Mars are more extreme in the
southern hemisphere because of its elliptical orbit.
Storms on Mars

Seasonal winds on Mars can drive huge dust storms.
What geological features tell us
water once flowed on Mars?
The surface of Mars appears to have ancient riverbeds.
Eroded
crater
The condition of craters indicates surface history.
Close-up of eroded crater
The Martian Surface Map
Volcanoes…as recent as 180 million years ago…
Past tectonic activity…
A *really* GRAND canyon…
A *even bigger* volcano
Differences in Hemispheres
Low-lying regions may once have had oceans.
Low-lying regions may once have had oceans.
Opportunity
Spirit
• 2004 Opportunity Rover provided strong evidence for abundant
liquid water on Mars in the distant past.
• How could Mars have been warmer and wetter in the past?
Today, most water
lies frozen
underground (blue
regions)
Some scientists
believe accumulated
snowpack melts
carve gullies even
today.
Why did Mars change?
Climate Change on Mars
No widespread
surface water for
3 billion years.
 Greenhouse
effect probably
kept surface
warmer before.
 Somehow Mars
lost most of its
atmosphere.

Climate Change on Mars


Magnetic field may have preserved early
Martian atmosphere.
Solar wind may have stripped atmosphere after
field decreased because of interior cooling.
Polar Climate Change
Exploring Mars
Winds on Mars
Wind trails
from “dust
devils”
Rivers on Mars
… & Earth!
… More
evidence
of water
Summary of Key Ideas
Mercury




Even at its greatest orbital elongations, Mercury can be
seen from Earth only briefly after sunset or before
sunrise.
The Mercurian surface is pocked with craters like the
Moon’s, but extensive, smooth plains lie between these
craters. Long cliffs meander across the surface of
Mercury. These scarps probably formed as the planet
cooled, solidified, and shrank.
The long-ago impact of a large object formed the huge
Caloris Basin on Mercury and shoved up jumbled hills on
the opposite side of the planet.
Mercury has an iron core, which fills more of its interior
than Earth’s core fills Earth.
Venus


Venus is similar to Earth in size, mass, and average
density, but it is covered by unbroken, highly reflective
clouds that conceal its other features from observers
using visible-light telescopes.
Although most of Venus’s atmosphere is carbon dioxide,
its dense clouds contain droplets of concentrated sulfuric
acid mixed with yellowish sulfur dust. Active volcanoes
on Venus may be a constant source of this sulfurous veil.
Venus


Venus’s exceptionally high temperature is caused by the
greenhouse effect, as the dense carbon dioxide
atmosphere traps and retains heat emitted by the planet.
The surface pressure on Venus is 90 atm, and the
surface temperature is 750 K. Both temperature and
pressure decrease as altitude increases.
The surface of Venus is surprisingly flat and mostly
covered with gently rolling hills. There are two major
“continents” and several large volcanoes. The surface of
Venus shows evidence of local tectonic activity but not
the large-scale motions that play a major role in
continually reshaping Earth’s surface.
Mars



Earth-based observers found that the Martian solar day
is nearly the same as that of Earth, that Mars has polar
ice caps that expand and shrink with the seasons, and
that the Martian surface undergoes seasonal color
changes.
A century ago, observers reported networks of linear
features that many perceived as canals. These
observations led to speculation about self-aware life on
Mars.
The Martian surface has many flat-bottomed craters,
several huge volcanoes, a vast equatorial canyon, and
dried-up riverbeds—but no canals formed by intelligent
life. River deltas and dry riverbeds on the Martian
surface indicate that large amounts of water once flowed
there.
Mars





Liquid water would quickly boil away in Mars’s thin
present-day atmosphere, but the planet’s polar ice caps
contain significant quantities of frozen water, and a layer
of permafrost exists beneath parts of the regolith.
The Martian atmosphere is composed mostly of carbon
dioxide. The surface pressure is less than 0.01 atm.
Chemical reactions in the regolith, together with
ultraviolet radiation from the Sun, apparently act to
sterilize the Martian surface.
Mars has no global magnetic fields, but local fields
pierce its surface in at least nine places.
Mars has two potato-shaped moons, the captured
planetesimals Phobos and Deimos. Both are in
synchronous rotation with Mars.
Key Terms
3-to-2 spin-orbit
coupling
caldera
dust devil
greenhouse effect
hot-spot volcanism
northern vastness
(northern
lowlands)
retrograde rotation
scarp
southern highlands
WHAT DID YOU THINK?


Which terrestrial planet—Mercury, Venus, Earth,
or Mars—has the coolest surface temperature?
The nighttime side of Mercury, closest planet to
the Sun, is the coldest surface of any terrestrial
planet.
WHAT DID YOU THINK?


Which planet is most similar in size to Earth?
Venus is most similar to Earth in size.
WHAT DID YOU THINK?


Which terrestrial planet—Mercury, Venus, Earth,
or Mars—has the highest surface temperature?
Venus is hottest, its temperature raised above
that of Mercury by the greenhouse effect in its
atmosphere.
WHAT DID YOU THINK?


What is the composition of the clouds that
surround Venus?
The clouds are made primarily of sulfuric acid.
WHAT DID YOU THINK?


Does Mars have liquid water on its surface
today? Did it have liquid surface water in the
past?
Mars has no liquid surface water today, but there
are very strong indications that it had liquid
water on its surface in the past.
WHAT DID YOU THINK?


Is life known to exist on Mars today?
No current life has yet been discovered on Mars,
but it may exist in underground water oceans.