Download Lesson 3 The Solar System

Lesson 3
The Solar
System
Stonehenge, England
How many planets do you see? Mars, Saturn, and Venus
are in a triangle above the center stone. Mercury is below
them to the left. Jupiter is much higher to the right. How
far away are these planets from Earth?
434
ENGAGE
ESS.42 Differentiate among moons, asteroids, comets, meteoroids, meteors, and
meteorites (ESS-M-C2) ESS.43 Describe the characteristics of the inner and outer
planets (ESS-M-C2) ESS.45 Identify Earth’s position in the solar system (ESS-M-C5)
Materials
How far apart are the planets?
Purpose
Make a model that shows the distances between
the planets using astronomical units (AU), where
one AU equals the average distance between Earth
and the Sun. This distance is about 149,591,000 km
(92,960,000 mi).
Procedure
• paper towels
Let the length of each paper towel equal 1 AU.
Using the information on the chart, roll out the
number of paper towels you need to show the
distance from the Sun to Neptune.
• markers
• ruler
• masking tape
Make a Model Mark the location of the Sun
Step
at one end. Measure the distance that each
planet would be from the Sun and draw the
planet on the paper towel.
Distances of the Planets from the Sun
Draw Conclusions
Interpret Data Compare the distances
between Mercury and Mars, Mars and
Jupiter, and Jupiter and Neptune. Which
are farthest apart?
Infer What can you conclude about
the distances between the planets in
the solar system?
Explore
Planet
Distance in AU
Mercury
0.4
Venus
0.7
Earth
1
Mars
1.5
Jupiter
5.2
Saturn
9.5
Uranus
19.2
Neptune
30
More
Your model has all of the planets in a line.
How could you make a model to show the
positions of the planets at a specific time?
Write instructions that others can follow
to make the model.
Step
SI.12 Use data and information gathered to develop
an explanation of experimental results (SI-M-A4)
SI.14 Develop models to illustrate or explain
conclusions reached through investigation (SI-M-A5)
Also covers SI.15
435
EXPLORE
What is the solar system?
▶ Essential Question
What are the components
of our solar system?
ESS.42, ESS.43, ESS.45
▶ Vocabulary
planet, p. 436
solar system, p. 436
inner planet, p. 438
outer planet, p. 440
comet, p. 442
asteroid, p. 443
Many ancient observers believed that Earth
was the center of everything. They believed the
Sun and all the objects in the night sky revolved
around Earth in perfect circles. However, many
astronomers doubted this belief because the
planets moved in different ways.
meteor, p. 443
moon, p. 444
▶ Reading Skill
Infer
Clues
What I
Know
In ancient times, observers noticed that the
stars stayed the same distance from one another
as they moved across the night sky. However,
they noticed a few exceptions. Five of the tiny
bright lights appeared in different parts of the
sky every night. They did not stay the same
distance from the other stars. At other times
they were not present at all. The ancient Greek
observers named these objects planets, a word
that means “wanderer.” A planet is a large object
that orbits a star.
What I
Infer
▶ Technology
e-Glossary and e-Review online
at www.macmillanmh.com
In the early 1500s, the mathematician and
astronomer Nicolaus Copernicus argued that
Earth rotated on its axis and revolved around the
Sun. His view changed how later astronomers
understood the stars and planets.
Earth is one of eight planets in our solar
system. A solar system is a star and the objects
that orbit it. The eight planets in our solar system
revolve around the Sun in elliptical orbits. Their
order from nearest to farthest from the Sun is
Mercury, Venus, Earth, Mars, Jupiter, Saturn,
Uranus, and Neptune.
Quick Check
Infer If scientists discovered a large object
moving around a distant star, what would they
call it?
Critical Thinking Is a moon that is larger than
▲ Earth is the third planet
from the Sun.
436
EXPLAIN
many of the planets in a solar system also a
planet? Explain your answer.
The Solar System
Venus
Sun
Mercury
Mars
Earth
Jupiter
asteroid belt
Uranus
Saturn
Planetary Data
Radius at
the Equator
(km)
Mean Surface
Temperature
(°C)
Surface
Materials
Rings
Mercury
2,440
179
rocks
no
Venus
6,052
482
rocks
no
Earth
6,378
15
rocks
no
Mars
3,397
-63
rocks
no
Jupiter
71,492
-121
gases
yes
Saturn
60,268
-125
gases
yes
Uranus
25,559
-193
gases
yes
Neptune
24,746
-193 to -153
gases
yes
Planet
Name
Neptune
Read a Table
Which planet has the warmest surface
temperature?
Clue: Find the highest temperature in the
mean surface temperature column.
437
EXPLAIN
What are the inner planets?
The inner planets are closer to the Sun than the asteroid belt.
These planets are Mercury, Venus, Earth, and Mars. Although
each inner planet has unique features, the inner planets have
common characteristics. For example, the inner planets all have
surfaces made of rock. Because of these rocky surfaces, the inner
planets are also called the terrestrial planets. The inner planets’
orbits are also spaced close together. These planets have few or
no moons, and none of them have rings.
Venus
Mercury
Distance From the Sun: 108 million km
(67 million mi)
Distance From the Sun: 58 million km
(36 million mi)
Mass: 0.82 × Earth
Mass: 0.06 × Earth
Number of Moons: 0
Surface Gravity: 0.38 × Earth
Surface Characteristics: The surface of
Venus shows evidence of violent volcanic
activity in the past. Venus has shield and
composite volcanoes similar to those
found on Earth. Long rivers of lava have
been seen on Venus.
Number of Moons: 0
Surface Characteristics: Mercury’s
surface looks a lot like the Moon’s
surface. It is heavily scarred with craters.
These craters were formed when
meteorites smashed into the planet’s
surface.
Special Features: Mercury has no true
atmosphere. Because Mercury does
not have an atmosphere, daytime
temperatures are extremely
high and nighttime
temperatures are
extremely low.
The sizes of Mercury, Venus, and Mars
are shown compared to Earth.
438
EXPLAIN
Surface Gravity: 0.91 × Earth
Special Features: A day on Venus is
longer than its year. Venus rotates once
every 243 Earth days and revolves around
the Sun in 225 Earth days. Venus also
rotates in the direction opposite Earth’s
rotation. Pressure at the surface of
Venus is about 90 times the atmospheric
pressure at Earth’s surface. This pressure
is enough to crush
a spacecraft.
Earth
Distance From the Sun: 150 million km
(93 million mi)
Planet Sizes SI.14, SI.15
Number of Moons: 1
Use Numbers Using a scale of
2,000 km = 1 cm, find the diameter
of each planet in centimeters.
Surface Characteristics: There might
once have been as many craters on
Earth as there are on Mercury. However,
erosion on Earth caused these craters to
disappear.
Make a Model Using a ruler and
scissors, cut circles out of poster
board to show the sizes of the
planets. Then label each planet.
Mass: 1 × Earth
Special Features: Earth is the largest
inner planet. It is the only planet in the
solar system known to support life as
we know it. Earth’s
atmosphere keeps
it from getting
too hot or
too cold.
Arrange the planets in order from
nearest to farthest from the Sun.
How do the sizes of the inner and
outer planets compare? Which
planet is about the same size as
Earth?
Mars
Distance From the Sun: 227.9 million km
(141.6 million mi)
Mass: 0.11 × Earth
Surface Gravity: 0.38 × Earth
Quick Check
Infer If you were on Venus, in what
Number of Moons: 2
direction would you see the Sun rise
and set? Explain.
Surface Characteristics: Mars is known
as the red planet because it has a
reddish surface color.
Critical Thinking How are the
Special Features: Mars’s axis
is tilted 25°. This means it
has seasons. Polar ice caps
melt in summer and form in
winter.
inner planets alike? How are they
different?
439
EXPLAIN
What are the outer planets?
There are four planets beyond the asteroid belt. These planets
are known as the outer planets. The outer planets include Jupiter,
Saturn, Uranus, and Neptune. Although they differ from each
other, these planets have some similarities. The outer planets are
made mostly of gas. They are sometimes called the gas planets.
Each of the gas planets has a metallic core and a thick atmosphere.
They are much larger than the inner planets. Their orbits are also
much farther apart than the orbits of the inner planets. All the
outer planets have rings and many moons. A day on an outer
planet is very short; they spin rapidly on their axes.
Jupiter
Distance From the Sun: 778 million km (483 million mi)
Mass: 318 × Earth
Surface Gravity: 2.53 × Earth
Number of Moons: 60+
Atmosphere Characteristics: The Great Red Spot is a huge
storm that has been blowing continuously for more than
400 years. Its winds can reach speeds of about 435 km/h
(270 mph). The storm is large enough to hold several Earths.
Scientists believe that a combination of sulfur and phosphorus
in the atmosphere gives this storm its color.
Special Features: Jupiter is so large that 1,000 Earths could
fit inside it. It also has more mass than all of the other planets
combined. Jupiter rotates faster than any other planet. It takes
only 9 hours and 56 minutes to rotate once on its axis.
Saturn
Distance From the Sun: 1,427 million km
(886.7 million mi)
Mass: 95 × Earth
Surface Gravity: 1.07 × Earth
Number of Moons: 60+
Atmosphere Characteristics: Saturn’s
atmosphere is similar to Jupiter’s. It
is composed mostly of hydrogen and
helium. Winds on Saturn move at about
1,800 km/h (1,100 mph) near the equator.
Special Features: Saturn is known for its
large, bright rings. The rings are made of
pieces of ice and rock.
440
EXPLAIN
Uranus
Distance From the Sun: 2,870 million km
(1,783 million mi)
Mass: 14.5 × Earth
Surface Gravity: 0.90 × Earth
Number of Moons: 20+
Atmosphere Characteristics: The bluegreen color of Uranus is due to methane
in the planet’s upper atmosphere.
Special Features: Uranus is unusual
because it looks as though it was
knocked on its side. Its axis of rotation
is tilted about 98° to its orbit. Scientists
think that a collision with
another object caused
Uranus to tip on its side.
The sizes of Saturn, Uranus,
and Neptune are shown
compared to Jupiter.
Neptune
Distance From the Sun: 4,500 million km
(2,796 million mi)
Mass: 17.2 × Earth
Surface Gravity: 1.14 × Earth
Number of Moons: 13
Atmosphere Characteristics: Like
Uranus, methane in its atmosphere gives
Neptune its blue color. Neptune has the
strongest winds of any planet. The winds
were measured to blow at speeds up to
2,000 km/h (1,250 mph) in some areas.
Many storms have been detected.
Special Features: Neptune has at least
five rings, none of which are very bright.
One of Neptune’s
moons, Triton, is
larger than Pluto.
Dwarf Planets
Pluto was once known as the ninth
planet. Pluto’s elongated orbit and small
size are different from those of the other
planets. Because of these differences,
scientists debated whether Pluto should
be classified as a planet. In August 2006,
the International Astronomical Union
officially reclassified Pluto as a dwarf
planet. Other dwarf planets include Ceres
and Eris. Ceres is found in the asteroid
belt between Mars and Jupiter. Eris is
slightly larger than Pluto and even farther
from the Sun.
Quick Check
Infer If scientists discover a new
planet that appears to be the same
color as Uranus, what can you infer
about its atmosphere?
Critical Thinking Why might the
outer planets have so many more
moons than the inner planets?
441
EXPLAIN
What are asteroids,
comets, and meteors?
Different types of small objects are
present in space. These objects include
comets, asteroids, and meteors.
Comets
A comet is a mixture of frozen
gases, ice, dust, and rock that moves
in an elliptical orbit around the Sun.
Comets are thought to be bits of
material left over from the formation
of the solar system about 4.6 billion
years ago.
When a comet is farther away from
the Sun, the gases and ice in the comet
are frozen. As the comet moves toward
the Sun, the core, or nucleus, of the
comet warms up. Some of the ice and
the dust in the core form a cloud, or
coma, around the nucleus. Together,
the nucleus and the coma make up the
head of the comet.
Comets have tails of ice
and gases.
442
EXPLAIN
As the comet gets closer to the Sun,
heat from the Sun pushes some of
the coma away from the comet. This
material forms a glowing tail that may
stretch millions of kilometers behind
the head. Sometimes two tails will
form. One tail is made of ice, and one
is made of gases.
Heat energy moves out from the
Sun in every direction. As a comet
moves around the Sun, the head stays
closest to the Sun and the tail trails
out behind it. No matter where the
comet is in its path around the Sun, the
comet’s tail always points away from
the Sun.
Comets orbit the Sun, but the
amount of time it takes them to orbit
the Sun varies. Halley’s Comet was the
first comet whose return was predicted.
The comet gets close to Earth about
every 76 years, most recently in 1986.
The next time Halley’s Comet will be
near Earth is in 2061.
The Leonid meteor shower occurs every year in mid-November.
Asteroids
An asteroid (AS•tuh•royd) is a rock
that revolves around the Sun. Most
of the thousands of asteroids in the
solar system are located between Mars
and Jupiter in the asteroid belt. Many
asteroids have irregular shapes and look
like potatoes. Some asteroids are less
than 2 km (1 mi) wide, while others can
be up to 800 km (500 mi) wide!
Ida is a heavily cratered,
irregularly shaped asteroid.
Meteors
The solar system is full of other
small objects. In space, these objects
are called meteoroids. If an object
crosses paths with Earth and enters
Earth’s atmosphere, it is called a
meteor. Most meteors burn up as they
travel through Earth’s atmosphere. If
a meteor does land on the ground, it is
called a meteorite.
Quick Check
Infer As scientists identify materials
in comets, what might they infer
about the materials that existed as
the solar system formed?
Critical Thinking Draw the location
of the tail and the head of a comet
as it moves around the Sun.
443
EXPLAIN
Various Moons of the Solar System
Ganymede
Moon
Deimos
Phobos
(Jupiter)
(Earth)
(Mars)
(Mars)
SCALE
SCALE
1 cm
1 cm
1,000 km
10 km
How do the moons
compare?
A moon is a natural object that
orbits a planet. Different planets have
different numbers and sizes of moons.
The inner planets have fewer moons
than the outer planets. Mercury and
Venus do not have moons. Earth has
one moon, and Mars has two.
With more than 60 moons, Jupiter
has the most moons of any planet
in the solar system. Saturn has more
than 45 moons. Astronomers have
discovered at least 27 moons around
Uranus and 13 moons orbiting
Neptune. As astronomers observe the
outer planets with better telescopes
and with space probes, they continue
to find more moons.
444
EXPLAIN
Moons are also called satellites
(SA•tuh•lites). A satellite is an object
in space that circles around another
object. While moons are natural
satellites, people also put objects into
space that orbit Earth or other planets.
These objects are called artificial
satellites. They include weather and
communications satellites as well as
space probes that orbit planets to
observe their surfaces.
The size of the moons in the solar
system varies. Some of the moons are
only a few kilometers wide. Jupiter’s
Ganymede is the largest moon in the
solar system. Ganymede is larger in
diameter than Pluto and Mercury.
Earth’s moon is also larger than Pluto
and is visible without a telescope.
Ganymede is the only other moon that
can be seen without a telescope.
Mimas
Hyperion
Miranda
(Saturn)
(Saturn)
(Uranus)
SCALE
1 cm
100 km
Read a Photo
How large are these moons?
Clue: Use the scales.
Forming Craters
Sometimes small objects in space
collide with large objects. When this
happens, the impact often forms a crater,
or a bowl-shaped hole, on the larger
object’s surface. Many moons have
craters. Craters vary in size because the
objects that hit a moon are different
sizes and travel at different speeds.
On Earth’s moon, the impact of
an object knocks the surface material
away so the rock underneath is
exposed. The surface material piles
around the edges of the crater. This
makes the Moon’s craters distinct and
easy to see from Earth.
Ganymede’s surface is made of ice
and rock. The dark rock is about
4 billion years old and the lightcolored rock is somewhat younger.
Craters are seen on both types of rock.
This means that objects have been
hitting Ganymede for at least 4 billion
years. Unlike those on the Moon,
craters on Ganymede are flat. This may
be because flowing ice on Ganymede’s
surface smooths out their edges.
Deimos, Mars’s smaller moon, is
composed of carbon-rich rock and ice.
Deimos’s surface has craters that have
been partially filled in by loose rock.
Quick Check
Infer How are a moon and an
artificial satellite different?
Critical Thinking What happens
when objects in space collide
with Earth?
445
EXPLAIN
What is Earth’s moon
like?
The Moon has been a source
of wonder throughout history. As
technology has progressed, people
have wanted to learn more and more
about the Moon. The greatest amount
of information about the Moon has
come from data gathered by the Apollo
missions, which included six Moon
landings between 1969 and 1972.
Several different features have
been identified on the Moon. Even
though the Moon and Earth are hit by
space objects at about the same rate,
the Moon has more craters. Earth’s
protective atmosphere causes most of
the incoming objects to burn up.
Maria (MAR•ee•uh) are large, dark,
flat surfaces on the Moon. The singular
form, mare (MAR•ay), means “sea”
in Latin. The smoothness of the maria
led people long ago to think that they
might be seas of water. Today scientists
think the maria formed when huge
space objects collided with the Moon’s
surface. These large areas of impact
then filled in with lava. When the lava
cooled, it gave the maria their smooth
appearance and dark color.
Highlands on the Moon are lightcolored regions near the lunar poles.
They are higher in elevation compared
to the maria. The surfaces of the
highlands have more craters than the
maria do, so scientists believe that
the highlands are geologically older
landforms.
Mountains on the Moon are found
around the edges of large maria. The
mountains probably formed from the
same impacts that formed the maria.
Mountain ranges on the Moon are
named after mountain ranges on Earth.
Valleys on the Moon are cigarshaped depressions. Perhaps the most
famous is the Alpine Valley on the
northeastern edge of Mare Imbrium.
New evidence suggest that the floors of
some deep Moon valleys may contain
small amounts of ice.
Quick Check
Infer What probably caused
mountains to form around the edges
of the maria?
Critical Thinking Why do people
who go to the Moon need to wear
space suits?
Mount Hadley Delta rises
about 4,000 m (13, 124 ft).
This image shows craters on
the Moon’s surface and a view
of Earth in the background.
446
EXPLAIN
Visual Summary
The solar system
is made of the
Sun, the planets
and their moons,
asteroids, meteoroids,
and comets.
The planets and moons
in the solar system
vary in size and
surface material.
The Moon has a surface
of different features,
including craters, maria,
and highlands.
Think, Talk, and Write
Vocabulary A mixture of frozen
gases, ice, dust, and rock that orbits
the Sun is a(n)
.
Infer If you knew probes that traveled
to Venus were crushed after a few hours,
what could you infer about atmospheric
pressure on Venus?
Clues
What I
Know
What I
Infer
Critical Thinking Earth is the only
planet known to have life. What do you
think makes this possible? What might
prevent life from existing on other planets?
Test Prep Which is the largest planet
Make a
Study Guide
Make a three-tab book.
Use the titles shown. On
the inside of each tab,
summarize what you
have learned.
in the solar system?
A Earth
B Mars
C Saturn
D Jupiter
Test Prep Which planet takes the
longest time to orbit the Sun?
A Mercury
B Venus
C Jupiter
D Uranus
Essential Question What are the
components of our solar system?
Writing Link
Art Link
Science Fiction
Planet Surfaces
Read The War of the Worlds by H.G.
Wells. Write a report about the novel.
Discuss how much of the story is based
on fact and how much is fiction.
Research the surface features of one
of the inner planets. Then draw an
illustration of what the planet’s surface
might look like.
-Review Summaries and quizzes online at www.macmillanmh.com
447
EVALUATE
Materials
Structured Inquiry
How can you model the solar system?
Purpose
construction
paper
markers
Our solar system consists of the Sun, planets, moons, and other
bodies, including asteroids, comets, and meteoroids. Each planet
has its own orbit around the Sun. What can a model of the solar
system show you? Construct a model of the solar system and use it to
compare the distances between planets.
Step
Procedure
Make a Model Make labels for
each planet and the Sun. Attach
each label to a dowel.
dowels
tape
30-m tape
measure
Planet
Mercury
Place the marker labeled Sun at
one end of a large open area.
Measure Use the table below to
construct your model. Measure
the scaled distance from the Sun
to Mercury, and place the marker
labeled Mercury in the ground.
Continue marking the distances
of the planets from the Sun.
Draw your model and record
your observations about the
solar system.
Distance from Sun
(in kilometers)
Distance from Sun, to Scale
(1 cm = 1,000,000 km)
57,900,000
58 cm
Venus
108,200,000
1 m, 8 cm
Earth
149,600,000
1 m, 50 cm
Mars
227,900,000
2 m, 28 cm
Jupiter
778,400,000
7 m, 78 cm
Saturn
1,426,700,000
14 m, 27 cm
Uranus
2,871,000,000
28 m, 71 cm
4,498,300,000
44 m, 98 cm
Neptune
448
EXTEND
Step
Step
Draw Conclusions
Interpret Data According to your
model, which planet is closest to the
Sun? Which planet is closest to Earth?
Interpret Data How does the distance
from the Sun to Jupiter compare to the
distance from Jupiter to Saturn? How
does the distance from the Sun to
Saturn compare to the distance from
Saturn to Uranus?
Guided Inquiry
Could you model the
solar system, including
the planets’ sizes and the
distances between the
planets?
Form a Hypothesis
Why is it so difficult to make a true scale
model of the solar system? Write your
answer in the form “If I try to model
the sizes of the Sun and all the planets
accurately, then...”
Test Your Hypothesis
Decide what data you need to collect to
make your model. Then choose a scale to
use for your model, and calculate the sizes
and positions of your model Sun and planets.
Open Inquiry
Think of a question about the solar
system to investigate. For example, are
the planets always the same distance
from the Sun, or do their distances
change? Design a data-collection
process or method of research to
answer your question. Your data must be
organized to test only one variable, or
one item being changed.
Remember to follow
the steps of the
scientific process.
Ask a Question
Form a Hypothesis
Test Your Hypothesis
Draw Conclusions
How easy would it be to make your model?
Explain.
Draw Conclusions
SI.33 Evaluate models, identify problems in design, and make recommendations
ffor improvement (SI-M-B4) SI.38 Explain that, through the use of scientific
processes and knowledge, people can solve problems, make decisions, and form
new ideas (SI-M-B6)
Also covers SI.14, SI.15
449
EXTEND