Lesson 25.2: Inner Planets
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C HAPTER
Chapter 1. Lesson 25.2: Inner Planets
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Lesson 25.2: Inner Planets
Key Concepts
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Earth
Mercury
Venus
Mars
Lesson Objectives
• Describe key features of each of the inner planets.
• Compare each of the inner planets to Earth and to one another.
Lesson Vocabulary
• day: amount of time it takes for a planet to complete one rotation on its axis
• inner planet: one of the four planets closest to the sun; Mercury, Venus, Earth, or Mars
• terrestrial planet: Earth or any of the other three Earth-like planets (Mercury, Venus, or Mars) that are solid,
dense, and rocky
• year: amount of time it takes for a planet to complete one revolution around the sun
Teaching Strategies
Introducing the Lesson
Introduce the inner, or terrestrial, planets by asking students to recall from the previous chapter (“Earth, Moon, and
Sun”) some of the most salient characteristics of planet Earth. Encourage a diversity of responses and list on the
board any characteristics they name that are shared with the other inner planets. Tell students they will learn in this
lesson about the planets in the solar system that resemble Earth in these ways.
Cooperative Learning
Students can collaborate to learn more about the inner planets by creating an illustrated booklet about them. Divide
the class into four groups and assign each group one of the four inner planets. Within groups, each student should
assume responsibility for finding one category of information (e.g., size, mass, and distance from the sun; atmosphere
and temperature range; interior layers and composition; surface features; unique properties; and so on), as well
as related images, about that planet. Then students within the group should collaborate to assemble all of the
information and images and create their booklet. Arrange a display of the booklets in the classroom, and encourage
students to examine the booklets created by other groups. Some suitable sources for information and images include:
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• http://nineplanets.org/
• http://www.neok12.com/Solar-System.htm
• http://airandspace.si.edu/research/resources/rpif/index.cfm
Activity
Have students do the activity “Find that Planet!” at the URL below. By doing the activity, they will learn about the
celestial coordinate system that astronomers use to identify the locations of objects in space. Students will use the
instructions provided to determine the position of a planet at a certain time and date. Then they will plot that position
on an appropriate sky map, choosing from a set provided. The final step is for students to actually find the planet in
the night sky using the sky map.
http://cse.ssl.berkeley.edu/SegwayEd/lessons/FindPlanets/Find-hmpg2.html
Differentiated Instruction
The four inner planets share certain similarities, but they also differ from one another in many important ways. To
help students sort out the similarities and differences, have them make a compare/contrast table for the inner planets.
They might compare them in terms of size, mass, distance from the sun, moons, atmosphere, temperature, and other
properties.
Enrichment
Mars has been the object of several space missions, in part because it seems to be the most suitable planet in our solar
system for life to have evolved. Suggest that students who want to learn more about Mars missions go to the URL
below. They will find a plethora of information about Mars and its exploration, ranging from Mars in pop culture to
the technology behind the Mars rovers. Encourage them to share the most interesting information they learn from
the site with the rest of the class in a brief oral report.
http://mars.jpl.nasa.gov/
Science Inquiry
Have students do the inquiry activity “Search for a Habitable Planet,” which is Lesson 4 in the following PDF
document. Students will define the life requirements of a variety of organisms and learn that these relate to
measurable characteristics of planets the organisms might inhabit. By evaluating these characteristics, students
will discover that Earth is the only natural home for us in our solar system and that Mars is the next most likely
home for life as we know it.
http://solarsystem.nasa.gov/docs/modelingsolarsystem_20070112.pdf
Common Misconceptions
Students commonly think that planets are too far away or too dim to be visible from Earth without a telescope.
In fact, five planets (other than Earth) are visible with the unaided eye: Mercury, Venus, Mars, Jupiter, and Saturn.
These planets are visible in our sky because they reflect sunlight and shine with a steadier light than distant twinkling
stars. In fact, the five planets tend to be quite bright. Tell students to read the article and view the images at the
following URL to see how clearly visible the planets can be.
http://earthsky.org/astronomy-essentials/visible-planets-tonight-mars-jupiter-venus-saturn-mercury#visible-planet
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Chapter 1. Lesson 25.2: Inner Planets
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in the CK-12 Earth Science for High School Workbook. Ask students to
complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 25.2 Quiz in CK-12 Earth Science for High School Quizzes and
Tests.
Points to Consider
The first humans may reach Mars sometime in the next few decades. What conditions will they face? Why do you
think we are going to Mars instead of Mercury or Venus?
Why are the four inner planets called terrestrial planets? What might a planet be like if it weren’t a terrestrial planet?
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