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Why Inner Planets Are Rocky

Interactive passage with audio narration, comprehension questions, and printable PDF.

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Format: Interactive (Online), Printable (PDF)
Grades: 5678
Subjects: scienceela
Standards: MS-ESS1-3
Languages: English, Spanish

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What's included

Reading passage

Reading comprehension

Audio narration

With word word highlighting

Comprehension quiz

Auto-graded

Writing activity

Open-ended response

Glossary & flashcards

Vocabulary practice

Differentiated version

Adapted for varied levels

Spanish translation

Bilingual support

About this reader

This 400-500 word informational science passage for grades 6-8 explores why the inner planets are rocky while outer planets are gaseous. Aligned with NGSS MS-ESS1-3 and MS-ESS1.B Earth and the Solar System standards, the passage explains how temperature differences in the early solar system determined planetary composition. Students learn about the protoplanetary disk, condensation of materials, and how solar wind pushed light gases outward. The passage includes audio integration for accessibility, 8-10 glossary terms, a simplified differentiated version for struggling readers, Spanish translations, and engaging activities including multiple-choice questions, writing prompts, and graphic organizers. Real-world connections help students understand how evidence from meteorites supports our understanding of planetary formation. This curriculum resource supports cause-and-effect reasoning and scientific explanation skills essential for middle school Earth and space science education.

Written by Workybooks TeamPublished by Workybooks

Sample passage and quiz content

CONTENT PREVIEW

The four planets closest to the Sun are made of rock and metal. Mercury, Venus, Earth, and Mars are called terrestrial planets because of their solid surfaces. Scientists explain that temperature and location determined what materials could form these worlds.

About 4.6 billion years ago, our solar system formed from a spinning cloud of gas and dust called a protoplanetary disk. The young Sun at the center was extremely hot. Close to the Sun, temperatures reached thousands of degrees. In this hot inner region, only materials with high melting points could remain solid. Metals like iron and nickel stayed solid, as did rocky minerals like silicates. Light materials such as hydrogen and helium remained as gases. These gases could not condense into solid or liquid form in the intense heat.

The young Sun also produced a powerful solar wind. This stream of charged particles blew outward through the solar system. The solar wind pushed light gases away from the inner regions. Hydrogen and helium drifted to the cooler outer solar system. There, temperatures were cold enough for these gases to remain and eventually form the giant gas planets. Meanwhile, the inner region was left with mostly rocky and metallic material.

Evidence shows that planets formed when small particles stuck together through gravity. In the inner solar system, only rock and metal particles were available. These materials clumped together over millions of years to form the four terrestrial planets. Scientists study meteorites that fall to Earth today. Many meteorites contain the same rocky and metallic materials found in inner planets. This supports the explanation that temperature and solar wind shaped planetary composition.

Understanding why inner planets are rocky helps scientists learn about planetary formation throughout the universe. Astronomers have discovered thousands of planets orbiting other stars. Many of these exoplanets show similar patterns. Rocky planets tend to orbit close to their stars, while gas giants orbit farther away. This pattern suggests that temperature and stellar wind affect planet formation in other solar systems too.

Interesting Fact: Mercury has the largest iron core relative to its size of any planet in our solar system. Scientists think a giant impact may have stripped away much of its rocky outer layer early in solar system history.

What are the four inner planets of our solar system called?

Gas giantsTerrestrial planetsIce planetsDwarf planets

What is a protoplanetary disk?

A type of rocky planetA stream of charged particles from the SunA spinning cloud of gas and dust from which planets formA piece of rock that falls from space

Why could only metals and rocks remain solid in the inner solar system?

They had high melting points and could withstand the intense heatThey were pushed there by solar windThey were lighter than gasesThey came from meteorites

What does the term 'condense' mean in the passage?

To heat up a materialTo change from a gas into a liquid or solid formTo blow outward through spaceTo stick together through gravity

What role did solar wind play in planet formation?

It heated the inner solar systemIt created the protoplanetary diskIt pushed light gases away from the inner regionsIt formed the terrestrial planets

How do scientists find evidence that supports the explanation of rocky planet formation?

By observing solar wind todayBy studying meteorites that contain similar rocky and metallic materialsBy measuring the temperature of the SunBy looking at gas giants

Based on the passage, what can scientists infer about exoplanets that orbit close to their stars?

They are likely to be gas giantsThey probably have no moonsThey are likely to be rocky planetsThey must be larger than Earth

If a planet formed in a very cold region far from a star, what materials would most likely make up that planet?

Only metals and rocksGases and ices that could condense in cold temperaturesOnly hydrogenThe same materials as Mercury

True or False: Light gases like hydrogen and helium could condense into solid form in the hot inner solar system.

TrueFalse

True or False: The pattern of rocky planets near stars and gas giants farther away has been observed in other solar systems.

TrueFalse