Inner Planets

Inner Planets

Middle School

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Learning Objectives

• Identify the four inner planets of our solar system.

• Describe the five main characteristics that define the inner planets.

• Explain why the inner planets are also referred to as terrestrial planets.

• Compare and contrast the inner planets with the outer planets based on their features.

Key Vocabulary

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Inner Planets

The four planets closest to the Sun, primarily composed of rock and metal materials.

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Terrestrial Planets

Another name for inner planets, which have a solid and rocky surface like our Earth.

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Orbit

The curved path a planet takes as it travels around the Sun.

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Composition

The materials or substances that something is made of, such as dense rock and iron.

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What Are the Inner Planets?

• The four inner planets are the planets that are closest to the Sun.

• In order, they are Mercury, Venus, Earth, and Mars.

• They are called terrestrial planets because of their solid, rocky surfaces.

  Tip to remember all the planets of the Solar system: My Very Educated Mother Just Served Us Nachos.

Multiple Choice

Which of the following lists the inner planets in the correct order from the Sun?

• Mercury, Venus, Earth, Mars

• Mars, Venus, Earth, Mercury

• Earth, Mars, Venus, Mercury

• Venus, Earth, Mars, Mercury

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Characteristics: Composition and Size

Rocky Composition

• ​Inner planets are made of rock and have a solid outer layer.

• ​​They formed from rock chunks located in the warmer areas of the early solar system.

• ​Because they are made of rock, the inner planets have high densities.

Smaller Size

• ​The four inner planets are much smaller compared to the outer planets.

• ​​The outer planets are mostly made of gas, contributing to their larger size.

• ​Of the inner planets, Mercury is the smallest in our solar system.

Multiple Choice

What are the two main characteristics of the inner planets described on this slide?

• They are rocky and smaller.

• They are gaseous and larger.

• They are made of ice and are very cold.

• They have many moons and slow orbits.

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Characteristics of Inner Planets

• Inner planets are hotter as they receive more solar energy.

• ​They have shorter and much faster orbits around the Sun.

• These planets have very few or no moons at all.

• Earth has one, Mars has two, and others have none.

Multiple Choice

Why are the inner planets hotter than the outer planets?

• Because they are closer to the Sun.

• Because they have hot iron cores.

• Because they are made of rock.

• Because they spin faster.

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Common Misconceptions

Misconception	Correction
All planets are made of the same materials.	The inner planets are made of rock, while the outer planets are gas giants.
A bigger planet means a warmer planet.	Temperature is determined by distance from the Sun.
All planets have at least one moon.	Mercury and Venus have no moons at all.

Multiple Choice

An unknown planet is described as being rocky, small, and having a short orbit. Based on this information, what type of planet is it most likely to be?

• An inner planet

• An outer planet

• A gas giant

• A dwarf planet

Multiple Choice

Which of the following is NOT a characteristic of terrestrial planets?

• Composed mainly of rock and metal

• Relatively small in size

• Have a solid surface

• Primarily made of gas

Multiple Choice

A scientist observes a new planet that is very large and has a composition of mostly gas. What can you logically conclude about its orbit?

• It will have a long orbital period (a long year).

• It will have a very short orbital period (a short year).

• Its orbit will be the same length as Earth's.

• It will be hotter than the inner planets.

Multiple Choice

How does the term 'terrestrial' help in understanding the fundamental difference between the inner and outer planets?

• It signifies that the inner planets have solid, Earth-like rocky surfaces, unlike the gaseous outer planets.

• It means the inner planets are the only ones capable of supporting life.

• It indicates that the inner planets are all the same size as Earth.

• It refers to the similar atmospheres of the inner planets.

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Summary

• The four inner planets are Mercury, Venus, Earth, and Mars.

• They are also called terrestrial planets because they have rocky surfaces.

• Inner planets are smaller, denser, and hotter than the outer planets.

• They have faster orbits, shorter years, and a combined total of three moons.

Poll

On a scale of 1-4, how confident are you about the characteristics of the inner planets?

• 1

• 2

• 3

• 4