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Table of Contents
Chapter: The Solar System
Section 1: Planet Motion
Section 2: The Inner Planets
Section 3: The Outer Planets
Section 4: Life in the Solar System
Planet Motion
1
Models of the Solar System
Geocentric Model
•  In the geocentric
model of the solar
system, Earth is
considered the
center and
everything else
revolves around it.
Planet Motion
1
Heliocentric Model
•  Earth-centered model held until 1543.
•  Nicholas Copernicus published a different
view.
•  Copernicus stated that the Moon
revolves around Earth.
•  Earth and the other planets revolve
around the Sun.
Planet Motion
1
Heliocentric Model
•  The apparent
motion of the
planets, the stars,
and the Sun is due
to Earth’s
rotation. This is
the heliocentric
model, or Suncentered model of
the solar system.
Planet Motion
1
Heliocentric Model
•  Galileo Galilei found evidence that
supported the ideas of Copernicus.
•  He observed that Venus went through
phases like the Moon’s.
•  He also saw moons in orbit around Jupiter.
Planet Motion
1
Understanding the Solar System
•  In the early 1600’s, Kepler discovered that
the planets travel around the Sun in ellipses,
not circles.
•  Planets travel at different speeds in their
orbits.
•  The astronomical unit (AU) equals the
average distance from Earth to the Sun,
about 150 million km.
Planet Motion
1
Classifying Planets
•  One system uses sizes and other
characteristics.
•  Those similar to Earth are called terrestrial
planets, giant planets are jovian planets.
•  Two other systems classify planets
by location.
Planet Motion
1
Classifying Planets
•  Planets whose orbits are between the Sun
and the asteroid belt as inner planets and
those beyond the asteroid belt as outer
planets.
•  The other system classifies planets whose
orbits are between Earth’s orbit and the Sun
as inferior planets, and those whose orbits
are beyond Earth’s orbit as superior planets.
Planet Motion
1
Other Solar Systems
•  Extrasolar planets—planets in orbit
around other stars—are helping astronomers
learn how planetary systems form.
•  Astronomers have devised new techniques
and instruments to find planets around other
stars.
Section Check
1
Question 1
Who was responsible for developing the
geocentric model of the solar system?
A. Aristotle
B. Copernicus
C. Galileo
D. Ptolemy
Section Check
1
Answer
The answer is D.
Ptolemy
presented his
geocentric
model of the
solar system in
140 A.D.
Section Check
1
Question 2
Approximately how long is an astronomical
unit?
A. 100 km
B. 100 million km
C. 150 million km
D. 200 billion km
Section Check
1
Answer
The answer is C. One astronomical unit equals
the average distance from Earth to the Sun,
about 150 million km.
Section Check
1
Question 3
_______ are planets in orbit around stars other
than our Sun.
A. Extrasolar planets
B. Extrasensory planets
C. Intersolar planets
D. Intrasolar planets
Section Check
1
Answer
The answer is A. Scientists have discovered
extrasolar planets around Upsilon Andromedae.
The Inner Planets
2
Planets near the Sun
•  The second-smallest and
closest planet to the Sun is
Mercury.
•  Mercury is covered by craters.
•  Mercury has a much larger
iron core than would be
expected and is missing some
lighter materials.
The Inner Planets
2
Planets near the Sun
•  Mercury’s large, solid core shrank much
more rapidly than its thin outer layers.
•  As the outer layers adjusted, they
wrinkled, forming dramatic cliffs
as high as 3 km.
•  Mercury has no true atmosphere.
•  Surface temperatures vary from
427ºC to -170ºC.
The Inner Planets
2
Venus
•  Venus is the second
planet from the Sun.
•  Venus is blanketed by
a dense atmosphere.
The Inner Planets
2
Venus
•  Heat radiated from Venus’s surface is
absorbed by the carbon dioxide gas,
causing what is called a greenhouse
effect.
•  Due to this intense greenhouse effect,
temperatures on the surface of Venus
are between 450ºC and 475ºC.
The Inner Planets
2
Earth
•  The third planet from
the Sun is Earth.
•  Temperatures on
Earth allow water
to exist as a solid,
a liquid, and a gas.
•  Ozone in Earth’s
atmosphere protects
life from the Sun’s
intense radiation.
The Inner Planets
2
Mars
•  The fourth planet from the Sun, Mars,
is called the red planet because of iron
oxide in some of the weathered rocks.
•  Other Martian
features are the polar
ice caps and changes
in the coloring of
Mars’s surface.
The Inner Planets
2
Mars
•  The polar ice caps
are made of frozen
carbon dioxide and
frozen water.
The Inner Planets
2
Mars
•  The Martian atmosphere is much thinner
than Earth’s and is composed mostly of
carbon dioxide with some nitrogen and
argon.
•  Mars has two small, heavily cratered
moons called Phobos and Deimos.
The Inner Planets
2
NASA on Mars
•  The Mariner 9 space probe orbited
Mars in 1971-1972.
•  Valles Marineris is a large canyon that
was discovered by this early mission.
•  Mariner 9 also found large, extinct
volcanoes.
The Inner Planets
2
The Viking Probes
•  In 1976, the Viking 1 and Viking 2
probes landed on Mars.
•  The Viking 1 and Viking 2 orbiters
photographed the entire surface of
Mars from orbit.
•  Landers conducted meteorological,
chemical, and biological experiments
on the planet’s surface.
The Inner Planets
2
Global Surveyor, Pathfinder,
and Odyssey
•  Global Surveyor showed that the walls of
Valles Marineris have distinct layers similar
to those of the Grand Canyon.
•  Mars Odyssey, provided evidence for water
as frost beneath a thin layer of soil in the far
northern and southern parts of Mars.
The Inner Planets
2
Global Surveyor, Pathfinder,
and Odyssey
•  The Mars Pathfinder and its rover,
Sojourner, gathered data that indicated that
iron in Mar’s crust may have been leached
out by groundwater.
Section Check
2
Question 1
Which planet is closest to the Sun?
A. Mars
B. Mercury
C. Earth
D. Venus
Section Check
2
Answer
The answer is B. Mercury is the closest
planet to the Sun. Venus is the second
planet from the Sun.
Section Check
2
Question 2
Which planet has size and mass similar
to Earth’s?
A. Jupiter
B. Mercury
C. Pluto
D. Venus
Section Check
2
Answer
The answer is D. Venus has similar size and
mass but the temperatures on its surface are
between 450º C and 475º C.
Section Check
2
Question 3
Earth is the __________ planet from the Sun.
A. second
B. third
C. fourth
D. fifth
Section Check
2
Answer
The answer is B. Mercury and Venus are closer
to the Sun than Earth.
The Outer Planets
3
Jupiter
•  The largest and fifth
planet from the Sun
is Jupiter.
•  It is composed
mostly of hydrogen
and helium.
The Outer Planets
3
Jupiter
•  Continuous storms
of swirling, highpressure gas have
been observed on
Jupiter.
•  The Great Red
Spot is the most
spectacular of
these storms.
The Outer Planets
3
Space Probes to Jupiter
•  In 1979, Voyager1 and Voyager 2 flew past
Jupiter, and the Galileo space probe reached
Jupiter in 1995.
•  The major discoveries of these probes
include information about the composition
and motion of Jupiter’s atmosphere,
characteristics of some of its moons and
the discovery of new moons.
The Outer Planets
3
Jupiter’s Moons
•  Four are large enough to be considered
small planets.
•  These Galilean moons of Jupiter are Io,
Europa, Ganymede, and Callisto.
The Outer Planets
3
Jupiter’s Moons
•  Ganymede is larger than the planet Mercury
and is the largest moon in the solar system.
•  Io is under a constant tug-of-war between
the gravities of Jupiter and Europa.
•  This heats up the interior of Io and causes
it to be the most volcanically active body
in the solar system.
The Outer Planets
3
Saturn
•  Saturn is the sixth planet from the Sun
and is known as the ringed planet.
•  Saturn is a large planet with a thick outer
atmosphere composed mostly of hydrogen
and helium with some ammonia, methane,
and water vapor.
The Outer Planets
3
Saturn’s Rings
•  Saturn’s rings are
composed of countless ice
and rock particles ranging
in size from a speck of dust
to tens of meters across.
•  Pictures of these rings
showed a density wave
and areas where the ring
material bends up and
down.
The Outer Planets
3
Uranus
•  Uranus, is the seventh planet from the Sun.
•  It is a large planet with 27 moons.
•  The atmosphere of Uranus contains hydrogen,
helium, and about two percent methane.
•  The methane gives the planet its blue-green
color.
The Outer Planets
3
Neptune
•  Neptune, another large planet similar in size
to Uranus, is the eighth planet from the Sun.
•  Neptune’s atmosphere is similar to that of
Uranus, but has a little more methane—
about 3 percent—causing it to look bluer.
The Outer Planets
3
Pluto
•  Pluto, is farther from the Sun than Neptune
during most of its orbit, it is considered the
ninth planet from the Sun.
The Outer Planets
3
Comets and Other Objects
•  A comet, is composed of dust rock
particles mixed with frozen water,
methane, and ammonia.
•  As a comet approaches the Sun, it begins
to vaporize. The released dust and gases
form a bright cloud called a coma around
the nucleus. The solar wind pushes on the
vaporized coma, forming a tail that always
points away from the Sun.
The Outer Planets
3
Comets and Other Objects
•  Most comets come from two places—a vast
disk of icy comets called the Kuiper Belt
near Neptune’s orbit and the Oort cloud.
•  Once in orbit around the Sun, comets
reappear at predictable times.
The Outer Planets
3
Comets and Other Objects
•  Rocky objects formed from material similar
to that of the planets are called asteroids.
•  Most asteroids are found in a belt between
the orbits of Mars and Jupiter.
•  Asteroids range in size from tiny particles
to objects 940 km in diameter.
The Outer Planets
3
Comets and Other Objects
•  Other rocky objects orbiting within
the solar system are meteoroids.
•  Meteoroids may enter the atmosphere.
•  Most burn up completely and we see
them as meteors or “shooting stars.”
•  Others do not burn completely and
strike Earth.
•  These are called meteorites.
The Outer Planets
3
Comets and Other Objects
•  Sedna has been labeled a distant
planetoid and with a diameter of 1,200
to 1,700 km, it is smaller than Pluto, but
larger than comets in the Kuiper Belt.
Section Check
3
Question 1
The fifth planet from the Sun is __________.
A. Jupiter
B. Neptune
C. Saturn
D. Pluto
Section Check
3
Answer
The answer is A. Jupiter is the largest planet in
the solar system.
Section Check
3
Question 2
Which of Jupiter’s large moons is closest to
Jupiter and the most volcanically active object
in the solar system?
A. Callisto
B. Europa
C. Ganymede
D. Io
Section Check
3
Answer
The answer is D. Jupiter exerts tremendous
gravitational pull on Io.
Section Check
3
Question 3
It takes Pluto __________ to orbit the Sun
one time.
A. 2 years
B. 24 years
C. 124 years
D. 248 years
Section Check
3
Answer
The answer is D. During part of its orbit, Pluto
is closer to the Sun than Neptune, but is still
considered to be the ninth planet from the Sun.
Life in the Solar System
4
Life as We Know It
Exotic Life on Earth
•  A research submarine, the Alvin, found
some interesting life-forms while exploring
hot, volcanic vents on the ocean floor.
•  Life-forms found included crabs, clams,
and tubeworms.
•  Alvin also discovered colonies of bacteria
living off the extremely hot material
spewing from volcanic vents.
Life in the Solar System
4
Can life exist on other worlds?
•  Extraterrestrial life is life on other
worlds.
•  Let’s take a look at some places where
scientists are searching for extraterrestrial
life.
Life in the Solar System
4
Mars
•  Evidence from space probes has shown
that Mars probably had large amounts
of water on its surface.
•  If life existed and left evidence, future
astronauts will find it.
Life in the Solar System
4
Europa
•  Europa’s ocean could hold more than
twice the amount of water that Earth’s
oceans hold.
•  If life can exist in extremely hot liquid
flowing from volcanic vents on Earth’s
ocean floor, could it not exist in a similar
environment if it exists on Europa?
Life in the Solar System
4
Titan
•  Saturn’s moon, Titan is larger than
Mercury and has an atmosphere composed
mostly of nitrogen.
•  The presence of hydrocarbons on the
surface of Titan interests exobiologists,
scientists who search for evidence of
life on other worlds.
Life in the Solar System
4
Titan
•  The apparent absence of large impact
craters indicates that Titan has
experienced internal geologic activity.
•  This activity could provide the energy
needed for organic molecules to develop
into the building blocks of life.
Section Check
4
Question 1
What is extraterrestrial life?
Answer
Extraterrestrial life is life that exists on other
planets.
Section Check
4
Question 2
What makes scientists think that Europa’s
ocean could contain life?
Answer
Scientists think that the ocean might be deep
and long-lasting, possibly even liquid water
that is warmed by Jupiter’s gravitational pull
on Europa.
Section Check
4
Question 3
Which performed tests for life on Mars?
A. Alvin
B. Huygens probe
C. Galileo probe
D. Viking probe
Section Check
4
Answer
The answer is D. The Viking experiments found
no evidence of life on Mars.
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