lesson 2 the inner planets...venus venus is the second planet from the sun. it has no moon. it is...

234 The Solar System The Inner Planets

Lesson 2

Scan Lesson 1. Read the lesson titles and bold words. Look at the pictures. Identify threefacts that you discovered about Newton’s second law of motion. Record your facts in your Science Journal.

The Inner PlanetsC

op

yrig

ht ©

McG

raw

-Hill E

du

ca

tion

.

I found this on page .

MercuryI found this on page .

Model the inner planets by drawing their orbits around the Sun. Color-code each planet and its orbit as follows: violet for Mercury, blue for Venus, green for Earth, and red for Mars.

Describe the inner planets by completing the diagram.

also called planets.

the four planetsthe Sun.

The inner planets

Organize facts about Mercury by completing the spider map.

Mercury

core: crust:

atmosphere:

diameter:

surface temperature:

mass:

surface appearance:

average distance from the Sun (AU):

Planets Made of RockI found this on page .

234_SC_ISE_G8_C08_L2_142789.indd234 234234_SC_ISE_G8_C08_L2_142789.indd234 234 3/4/15 11:56:45 AM3/4/15 11:56:45 AM

Co

pyri

gh

t ©

McG

raw

-Hill E

du

ca

tio

n.

The Inner Planets The Solar System 235

Planets Made of RockThe inner planets—Mercury, Venus, Earth, and Mars—are

also called terrestrial planets. Terrestrial planets are the planets closest to the Sun, are made of rock and metal, and have solid outer layers. Like Earth, the other inner planets also are made of rock and metallic materials and have a solid outer layer. As shown below, Mercury, Venus, and Earth have a solid inner core and a liquid outer core. The core of Mars is liquid with no solid part. However, the inner planets have different sizes, atmospheres, and surfaces.

What do you think? Read the two statements below and decide whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind.

Before Statement After

3. Earth is the only inner planet that has a moon.

4. Venus is the hottest planet in the solar system.

Key Concepts • How are the inner planets

similar?• Why is Venus hotter than

Mercury?• What kind of atmospheres

do the inner planets have?

Identify the Main Ideas Highlight the important ideas in each paragraph. Review these ideas as you study the lesson.

Visual Check1. Distinguish Number each structure in the figure from 1 to 4 in order from the outermost layer to the innermost layer.

Structure of Mercury, Venus, and Earth

Crust

Mantle

Liquid outer core Solid inner core

The Solar System

The Inner Planets

LESSON 2

CHAPTER 8

235_238_SC_ISE_G8_C08_L2_142789.235 235235_238_SC_ISE_G8_C08_L2_142789.235 235 3/4/15 11:57:34 AM3/4/15 11:57:34 AM

Co

pyrig

ht ©

McG

raw

-Hill E

du

ca

tion

.


Key Concept Check3. Apply Why is Venus hotter than Mercury?

Key Concept Check 2. Compare How are the inner planets similar?

MercuryMercury is the smallest planet and the planet closest to the

Sun. Mercury has no moon and no atmosphere. The strength of a planet’s gravity depends on its mass. Mercury’s small mass creates weak gravity that cannot hold on to an atmosphere. With no atmosphere there is no wind that moves energy across the planet’s surface. This results in temperatures as high as 450°C on the side of Mercury facing the Sun and as cold as - 170°C on the side facing away from the Sun.

Mercury’s SurfaceImpact craters, depressions formed by collisions with

objects from space, cover the surface of Mercury. There are smooth plains of solidified lava from long-ago eruptions. There are also high cliffs that might have formed when the planet cooled quickly, causing the surface to wrinkle and crack. Without an atmosphere, almost no erosion occurs on Mercury’s surface. As a result, features that formed billions of years ago have changed very little.

Mercury’s StructureThe structures of the inner planets are similar. Like all

inner planets, Mercury has a core made of iron and nickel. A mantle of silicon and oxygen surrounds the core. The crust is a thin, rocky layer above the mantle. Mercury has a large core, possibly formed by a collision with a large object during the planet’s formation.

VenusVenus is the second planet from the Sun. It has no moon.

It is about the same size as Earth. Venus rotates so slowly that its period of rotation is longer than its period of revolution. Unlike most planets, Venus rotates from east to west.

Venus’s AtmosphereThe atmosphere of Venus is about 97 percent carbon

dioxide. Its atmospheric pressure is nearly 90 times greater than Earth’s. Venus has almost no water, yet a thick layer of clouds covers the planet. The clouds are made of acid.

The Greenhouse Effect on VenusVenus is the hottest planet in the solar system. Its

temperature averages 460°C. The greenhouse effect causes the high temperatures. The greenhouse effect occurs when a planet’s atmosphere traps solar energy and causes the surface temperature to increase. The carbon dioxide in Venus’s atmosphere traps energy and heats up the planet. The planet would be 450°C cooler without the greenhouse effect.

Make a four-door book to organize your notes on the inner planets.

Mercury Earth

MarsVenus


Co

pyri

gh

t ©

McG

raw

-Hill E

du

ca

tio

n.


Key Concept Check6. Describe the atmosphere of each inner planet.

Venus’s Structure and SurfaceSolidified lava covers more than 80 percent of Venus’s

surface. The lava possibly came from volcanic eruptions.

EarthEarth is the third planet from the Sun. Unlike Mercury

and Venus, Earth has a moon.

Earth’s AtmosphereGases and a small amount of water vapor make up most

of Earth’s atmosphere. The gases and vapor produce a greenhouse effect that increases Earth’s average surface temperature. This effect and Earth’s distance from the Sun warm Earth. As a result, large bodies of liquid water can exist on Earth. Earth’s atmosphere also absorbs much of the Sun’s radiation. This protects the surface below. Earth’s protective atmosphere, liquid water, and moderate temperatures support a wide variety of life.

Earth’s StructureEarth has a solid inner core surrounded by a liquid

outer core. The outer core is surrounded by a mantle. Earth’s crust is above the mantle. The crust is broken into large plates that slide past, away from, or into each other. It is made mostly of oxygen and silicon. Natural forces constantly destroy Earth’s crust and create new crust.

MarsMars is the fourth planet from the Sun. It is about half

the size of Earth. Unlike the other inner planets, Mars has no solid inner core. Its core is liquid. Mars has two moons. Space probes have visited Mars; however, they found no liquid water or life on the planet.

Mars’s AtmosphereThe atmosphere of Mars is much less dense than that of

Earth. It is about 95 percent carbon dioxide. Temperatures range from about -125°C at the poles to about 20°C at the equator. Winds on Mars produce great dust storms.

Mars’s SurfaceIron oxide in the soil gives Mars its reddish color. The

Martian canyon Valles Marineris is as long as the United States. The Martian volcano Olympus Mons is the largest known mountain in the solar system. Mars has polar ice caps made of frozen carbon dioxide and ice. Craters cover the southern hemisphere of Mars. The northern hemisphere is smoother and appears to be covered by lava flows.

Reading Check4. Explain Why is there life on Earth?

Reading Check5. Compare Earth’s inner core with the inner core of Mars.


Co

pyrig

ht ©

McG

raw

-Hill E

du

ca

tion

.


Mini Glossary

Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?

What do you think

END OF LESSON

Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.

ConnectED

greenhouse effect: occurs when a planet’s atmosphere traps

solar energy and causes the surface temperature to increase

terrestrial planet: Earth or another inner planet

1. Review the terms and their definitions in the Mini Glossary. Write a sentence that explains how the greenhouse effect benefits life on Earth.

2. Fill in the chart below to match the inner planets with their features.

Inner planets: Earth, Venus, Mars, and Mercury

a. b. c. d.

Features:• Closest to the Sun

• Smallest of all planets

• No moon

• Weak gravity

• No atmosphere

• Wide temperature range

• Impact craters cover the surface

Features:• Second-closest to the

Sun

• No moon

• High atmospheric pressure

• Covered by acid clouds

• Hottest planet in the solar system

• Surface is mostly solidified lava

Features:• Third-closest to the Sun

• One moon

• Atmosphere protects surface from much of the Sun’s radiation

• Large bodies of liquid water

• Moderate temperature range

• Crust made up of large sliding plates

Features:• Fourth-closest to the

Sun

• Two moons

• Great dust storms

• Reddish color

• Valles Marineris: a huge canyon

• Olympus Mons: largest mountain in the solar system

• Polar ice caps

3. Explain why Earth has an atmosphere but Mercury does not.



Lesson 2 | The Inner Planets (continued)C

op

yri

gh

t ©

McG

raw

-Hill E

du

ca

tio

n.

Compare and contrast characteristics of Mercury and Venus.

Venus• thick atmosphere

Mercury• no atmosphere

Both• inner planets

Explain why Venus is hotter than Mercury.

Sort facts about Earth and Venus. Place the number of each fact in the Venn diagram.

1. has a greenhouse effect

2. has extremely high temperature

3. has water in its atmosphere

4. year is longer than its day

5. atmosphere mostly carbon dioxide

6. rotates counter-clockwise

7. rotates clockwise

8. a terrestrial planet

9. an inner planet10. has a moon11. has water on

its surface12. can support life

EarthBoth

Venus

EarthI found this on page .


Ven usI found this on page .

239_240_SC_ISE_G8_C08_L2_142789.Sec1:239 Sec1:239239_240_SC_ISE_G8_C08_L2_142789.Sec1:239 Sec1:239 3/4/15 11:42:51 PM3/4/15 11:42:51 PM


Lesson 2 | The Inner Planets (continued)C

op

yrig

ht ©

McG

raw

-Hill E

du

ca

tion

.

Contrast Earth and Mars. Circle the best answers.

Earth Mars

Which phases of water are found there?

ice liquid water vapor

ice liquid water vapor

What is its distance to the Sun?

distance > 1 AUdistance = 1 AUdistance < 1 AU

distance > 1 AUdistance = 1 AUdistance < 1 AU

Describe the appearance of its surface.

How many moons does it have? one two one two

Summarize information about the inner planets. Place a check mark in each box that a pplies to each planet.

Mercury Venus Earth Mars

Atmosphere

Inner and outer core

Liquid outer core

Liquid core, only

Solid inner core

Atmosphere 90% CO2

Cratered surface

Liquid water on surface

Ice on surface

A moon or moons

Mantle and crust

Signs of volcanic action


MarsI found this on page .

From Earth, Venu s looks like a very bright star in the night sky. If you could look at Earth from Venus, what would Earth look like? Explain your answer.

239_240_SC_ISE_G8_C08_L2_142789.Sec1:240 Sec1:240239_240_SC_ISE_G8_C08_L2_142789.Sec1:240 Sec1:240 3/4/15 11:43:52 PM3/4/15 11:43:52 PM

lesson 2 the inner planets...venus venus is the second planet from the sun. it has no moon. it is...

Documents