Download The inner solar system has rocky planets.

KEY CONCEPT
The inner solar system
has rocky planets.
Sunshine State
STANDARDS
SC.E.1.3.1: The student
understands the vast
size of our Solar
System and the relationship of the planets
and their satellites.
SC.E.1.3.2: The student
knows that available
data from various satellite probes show the
similarities and differences among planets
and their moons in the
Solar System.
SC.H.1.3.2: The student
knows that the study
of the events that led
scientists to discoveries
can provide information about the inquiry
process and its effects.
BEFORE, you learned
NOW, you will learn
• Planets are closer together in
the inner solar system than in
the outer solar system
• Planets formed along with
the Sun
• Gravity made planets round
• How four processes change the
surfaces of solid planets
• How atmospheres form and
then affect planets
• What the planets closest
to the Sun are like
EXPLORE Surfaces
How does a planet’s mantle affect its surface?
MATERIALS
PROCEDURE
1
Dampen a paper towel and place it on top
of two blocks to model a crust and a mantle.
• 2 blocks
• paper towel
• newspaper
2 Move one block. Try different amounts
of motion and different directions.
WHAT DO YOU THINK?
• What happened to the paper towel?
• What landforms like this have you seen?
VOCABULARY
terrestrial planet p. 749
tectonics p. 750
volcanism p. 750
The terrestrial planets have rocky crusts.
Scientists study Earth to learn about other planets. They also study
other planets to learn more about Earth. The terrestrial planets are
Mercury, Venus, Earth, and Mars—the four planets closest to the Sun.
They all have rocky crusts and dense mantles and cores. Their insides,
surfaces, and atmospheres formed in similar ways and follow similar
patterns. One planet—Earth—can be used as a model to understand the others. In fact, the term terrestrial comes from terra,
the Latin word for Earth.
Earth
Most of Earth’s rocky surface is hidden by water. More details about Earth
and other planets are listed in the Appendix at the back of this book.
Mass 6 1024 kg
Diameter 12,800 km
Average distance from Sun 1 AU
Orbits in 365 days
Rotates in 24 hours
Chapter 21: Our Solar System 749
Processes and Surface Features
All terrestrial planets have layers. Each planet gained energy from the
collisions that formed it. This energy heated and melted the planet’s
materials. The heaviest materials were metals, which sank to the center
and formed a core. Lighter rock formed a mantle around the core.
The lightest rock rose to the surface and cooled into a crust.
Four types of processes then shaped each planet’s rocky crust.
The processes acted to different extents on each planet, depending
on how much the crust and inside of the planet cooled.
reading tip
1
Earth’s crust is split into large pieces called tectonic plates.
These plates are moved by Earth’s hot mantle. Mountains, valleys,
and other features form as the plates move together, apart, or along
each other. The crusts of other terrestrial planets are not split into
plates but can be twisted, wrinkled up, or stretched out by the
mantle. Tectonics is the processes of change in a crust due to the
motion of hot material underneath. As a planet cools, the crust
gets stiffer and the mantle may stop moving, so this process stops.
2
Volcanism
3
Weathering and Erosion
4
Impact Cratering
Compare what you read
about each type of feature
with the pictures and
diagrams on page 751.
RESOURCE CENTER
CLASSZONE.COM
Find out more about
impact craters on Earth
and other space objects.
Tectonics
A second process, called volcanism, occurs when
molten rock moves from a planet’s hot interior onto its surface.
The molten rock is called lava when it reaches the surface through
an opening called a volcano. On Earth, lava often builds up into
mountains. Volcanoes are found on Earth, Venus, and Mars.
Lava can also flow onto large areas and cool into flat plains like
the lunar maria. When the inside of a planet cools enough, no
more molten rock reaches the surface.
You have read about weathering on
Earth and the Moon. Weather or small impacts break down rocks.
The broken material is moved by a group of processes called erosion.
The material may form dunes, new layers of rock, or other features.
On Earth, water is important for weathering and erosion. However,
similar things happen even without water. Wind can carry sand
grains that batter at rocks and form new features. Even on a planet
without air, rock breaks down from being heated in the daylight
and cooled at night. The material is pulled downhill by gravity.
A small object sometimes hits a planet’s surface
so fast that it causes an explosion. The resulting impact crater is
often ten times larger than the object that produced it. On Earth,
most craters have been erased by other processes. Impact craters
are easier to find on other planets. If a planet or part of a planet is
completely covered with impact craters, then the other processes
have not changed the surface much in billions of years.
check your reading
750 Unit 6: Space Science
What processes affect the surfaces of terrestrial planets?
Features of Rocky Planets
The processes that shape features on a planet’s surface can be divided into
four types. The features can tell you different things about the planet.
1
Tectonics
A hot mantle can move and
distort the crust above it.
This system of mountains and valleys on Earth
formed as the crust was stretched.
3
Weathering and Erosion
2
Volcanism
Hot, molten rock can flow
or explode out onto the surface of a planet. At this volcano on Venus, lava
flowed onto the surface several times.
4
Impact Cratering
A small space object can hit a planet’s surface
and leave a crater. Because the other processes
on Mercury are weak,
newer craters can be seen
on a background of older,
more eroded craters.
Rock can be broken down
and moved. In this region
of Mars, material broken from a cliff was
moved by erosion into new slopes and dunes.
Which two processes happen because of hot material beneath the surface?
Chapter 21: Our Solar System 751
Layers
How do the layers inside of planets form?
SKILL FOCUS
Using models
In this model, the materials you use represent different rocks and metals that
make up the solid planets.
PROCEDURE
1
Put pieces of gelatin into the container until it is about one-quarter full.
2 Mix in a spoonful each of sand and wax. Use the spoon to break the gelatin
into small pieces as you mix. Remove the spoon.
3 Place the container in a bowl of hot tap water (about 70°C) and observe
what happens as the gelatin melts.
MATERIALS
•
•
•
•
•
•
container
spoon
firm gelatin
sand
wax pieces
bowl of hot
tap water
TIME
WHAT DO YOU THINK?
• What happened to each of the materials when the gelatin melted?
40 minutes
• How do the results resemble the core, mantle,
and crust of Earth and other planets?
CHALLENGE How might you improve
this model?
Atmospheres
Atmospheres on terrestrial planets mainly formed from gases that
poured out of volcanoes. If a planet’s gravity is strong enough, it pulls
the gases in and keeps them near the surface. If a planet’s gravity is
too weak, the gases expand into outer space and are lost.
Venus, Earth, and Mars each had gravity strong enough to hold
heavy gases such as carbon dioxide. However, the lightest gases—
hydrogen and helium—escaped into outer space. The atmospheres
of Venus and Mars are mostly carbon dioxide.
FLORIDA
Content Review
reminder
Remember that Earth’s
atmosphere is like a blanket
that protects Earth, as you
learned in grade 6.
An atmosphere can move energy from warmer places to cooler
places. This movement of heat energy makes temperatures more
uniform between a planet’s day side and its night side and between
its equator and its poles. An atmosphere can also make a planet’s
whole surface warmer by slowing the loss of energy from the surface.
After Earth formed, its atmosphere of carbon dioxide kept the
surface warm enough for water to be liquid. Oceans covered most of
Earth’s surface. The oceans changed the gases of the atmosphere, and
living organisms caused even more changes. Earth’s atmosphere is
now mostly nitrogen with some oxygen.
check your reading
752 Unit 6: Space Science
Why is the solid Earth surrounded by gases?
no data
Craters cover the surface
of Mercury.
Mercury, like the Moon, has smooth plains
and many craters. The processes at work
on Earth also affected Mercury.
Long, high cliffs stretch
across Mercury’s surface. Scientists
think that Mercury’s huge core of iron
shrank when it cooled long ago.
The crust wrinkled up, forming cliffs,
as the planet got a little smaller.
Tectonics
Parts of the surface were
covered with lava long ago. Large, smooth
plains formed. The plains are similar to
lunar maria.
Volcanism
Small impacts and temperature changes have broken rock. Gravity has moved broken
material downhill.
Weathering and Erosion
Round features cover much of the surface. These
craters show that the other processes have not changed Mercury’s
surface very much for a long time.
Mercury
This map of Mercury was
made from many images
taken by one spacecraft.
The blank patches show
areas that were not
mapped by the spacecraft.
Impact Cratering
Mercury has the longest cycle of day and night of the terrestrial
planets—three months of daylight and three months of darkness.
There is no atmosphere to move energy from the hot areas to the
cold areas. In the long daytime, it can get hotter than 420°C (about
800°F)—hot enough to melt lead. During the long, cold night, the
temperature can drop lower than –170°C (about –280°F).
Check Your Reading
Mass 6% of Earth’s mass
Diameter 38% of Earth’s
diameter
Average distance
from Sun 0.39 AU
Orbits in 88 Earth days
Rotates in 59 Earth days
How is Mercury similar to the Moon?
cliff
Craters of all sizes cover
Mercury’s surface, but
there are also flat lava
plains and cliffs from
long ago.
craters
Chapter 21: Our Solar System 753
MAIN IDEA AND DETAILS
When you see a new
heading, remember to take
notes about important ideas.
Volcanoes shape the surface of Venus.
The planet Venus is only a little smaller than Earth and orbits a little
closer to the Sun. As a result, Venus is sometimes called Earth’s sister
planet. However, Venus is different from Earth in important ways.
Venus takes about eight months to turn just once on its axis.
Unlike most other planets, Venus rotates and orbits in opposite directions. The rotation and orbit together produce very long days and
nights—two months of daylight followed by two months of darkness.
Thick clouds make it
impossible to see Venus’s
surface in visible light.
This inset shows a map of
Venus that scientists made
using radio waves.
The atmosphere of Venus is very dense. Air pressure on Venus is
90 times that on Earth. Venus’s atmosphere is mostly carbon dioxide.
This gas slows the loss of energy and makes the surface very hot.
The ground temperature on Venus is about 470°C (about 870°F). The
atmosphere of Venus moves energy around so well that the long nights
are as hot as the days and the poles are as hot as the equator. In addition, there are droplets of sulfuric acid, a corrosive chemical, in the
atmosphere. These droplets form thick white clouds that completely
cover the planet and hide the surface.
Like Mercury, Venus is affected by the same four types of processes
that change Earth’s surface. Scientists think that tectonics and volcanism
may still be changing Venus’s surface today.
Patterns of cracks and cliffs have formed as movements of
the hot mantle have stretched, wrinkled, and twisted the surface.
Tectonics
Most of the surface of Venus has been covered with lava in the last billion years or so. Volcanoes
and flat lava plains are found all over the surface.
Volcanism
Venus
Venus is nearly the size of Earth but has a thicker atmosphere
and is much hotter than Earth. The surface is rocky, as you can
see in the image below.
Mass 82% of Earth’s mass
Diameter 95% of Earth’s diameter
Average distance from Sun 0.72 AU
Orbits in 225 Earth days
Rotates in 243 Earth days
weathered and eroded rock
spacecraft
754 Unit 6: Space Science
Venus is too hot to have liquid water, and
the winds do not seem to move much material. Erosion may be slower
on Venus than on Earth.
Weathering and Erosion
Round craters mark the surface here and there.
Older craters have been erased by the other processes. Also, Venus’s
thick atmosphere protects the surface from small impacts.
Impact Cratering
check your reading
Why is Venus not covered with craters?
Erosion changes the appearance of Mars.
Mars is relatively small, with a diameter about half that of Earth.
The orange color of some of the surface comes from molecules
of iron and oxygen—rust. Mars has two tiny moons. They were
probably once asteroids that were pulled into orbit around Mars.
Mars
The atmosphere of Mars is
thin but causes weathering
and erosion.
Surface of Mars
The same processes that affect the other terrestrial planets
affect Mars.
Valleys and raised areas formed on Mars as the mantle
moved. One huge system of valleys, called Valles Marineris,
is long enough to stretch across the United States.
Tectonics
Volcanism Most of the northern hemisphere has
smooth plains of cooled lava. Several volcanoes
are higher than any mountain on Earth.
The lava must have built up in the same spot
for a long time, so scientists have inferred
that the crust of Mars has cooled more than
Earth’s crust. On Earth, the tectonic plates
move, so chains of smaller volcanoes form
instead of single larger volcanoes.
Mass 11% of Earth’s mass
Diameter 53% of Earth’s
diameter
Average distance
from Sun 1.5 AU
Orbits in 1.9 Earth years
Rotates in 25 hours
volcanoes
Valles Marineris
Fast winds carry
sand that breaks down rocks. Wind and gravity
move the broken material, forming new features
such as sand dunes. There are also landforms
that look like the results of gigantic flash floods
that happened long ago.
Weathering and Erosion
Round craters cover much of the
southern hemisphere of Mars. Many craters are very old
and eroded. A few impact craters on the volcanoes make scientists
think that the volcanoes have not released lava for a long time.
Impact Cratering
Chapter 21: Our Solar System 755
The sky of Mars is made
red by dust that the wind
picks up and carries to
new places.
Gases and Water on Mars
The atmosphere of Mars is mostly carbon dioxide. The air pressure is
only about 1 percent of the air pressure on Earth. The gas is not dense
enough to keep the surface warm or to move much energy from cold
areas to warmer areas. Therefore, temperatures may reach almost
20°C (about 60°F) in the daytime and –90°C (–130°F) at night.
The large differences in temperature produce fast winds. The winds
cause gigantic dust storms that sometimes cover most of the planet.
Like Earth, Mars has polar caps that grow in winter and shrink in
summer. However, the changing polar caps of Mars are made mostly of
frozen carbon dioxide—dry ice. The carbon dioxide of the atmosphere
can also form clouds, fog, and frost on the ground.
There is no liquid water on the surface of Mars today. Any water
would quickly evaporate or freeze. However, there were floods in the
past, and there is still frozen water in the ground and in one polar cap.
Water is important for life and will also be needed to make rocket fuel
if humans are ever to make trips to Mars and back.
check your reading
In what ways is Mars different from Earth?
KEY CONCEPTS
CRITICAL THINKING
1. What are the four types of
processes that shape planets’
surfaces? For each, give one
example of a feature that the
process can produce.
4. Compare and Contrast
Make a chart with columns for
the four types of processes and
for an atmosphere. Fill out a
row for each planet.
2. How can an atmosphere
affect the temperature of a
planet’s surface?
5. Apply If a planet had a surface with craters but no other
features, what could you say
about the inside of the planet?
3. Which terrestrial planet has the
oldest, least-changing surface?
756 Unit 6: Space Science
CHALLENGE
6. Infer Describe how a hot
mantle can affect a planet’s
atmosphere. Hint: Which of
the four processes is involved?