Premium

What Are Dwarf Planets

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

No ratings yet

Just this resource

$1.50

One-time purchase

Best value

Unlock everything

$19.99/yr

5,000+ resources, AI tools

Unlock above to use these actions

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

Send Feedback / Report an Issue

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 engaging 500-word science passage for grades 6-8 explores what dwarf planets are and how they differ from regular planets. Students learn about the International Astronomical Union (IAU) criteria that define dwarf planets: they must orbit the Sun, have sufficient mass to achieve a round shape, but have not cleared their orbital paths of debris. The passage introduces the five officially recognized dwarf planets—Pluto, Ceres, Eris, Makemake, and Haumea—and explains their unique characteristics and locations in our solar system. Aligned with NGSS standards MS-ESS1.B and MS-ESS1-3, this audio-integrated resource helps students understand Earth's place in the universe and the scale of the solar system. The passage includes real-world examples, such as Pluto's reclassification in 2006, and connects to broader concepts about how scientists classify celestial objects. Perfect for middle school science curriculum, this passage develops scientific vocabulary while building foundational knowledge about our solar system's diverse objects.

Written by Workybooks TeamPublished by Workybooks

Sample passage and quiz content

CONTENT PREVIEW

An artist's concept showing the size of the best known dwarf planets compared to Earth and its moon (top). Eris is left center; Ceres is the small body to its right and Pluto and its moon Charon are at the bottom. Dwarf Comparison1" by NASA / Wikimedia Commons

A dwarf planet is a type of celestial object that orbits the Sun. It has enough mass to pull itself into a round shape. However, it has not cleared its orbital path of other debris. This third requirement separates dwarf planets from regular planets. The International Astronomical Union (IAU) created these criteria in 2006 to classify objects in our solar system.

Scientists recognize five official dwarf planets in our solar system. Pluto is the most famous dwarf planet. It was once considered the ninth planet until scientists reclassified it. Ceres orbits in the asteroid belt between Mars and Jupiter. It is the only dwarf planet located in the inner solar system. Eris is slightly smaller than Pluto but contains more mass. Scientists discovered Eris in 2005, and its discovery led to Pluto's reclassification. Makemake and Haumea are the other two recognized dwarf planets. Both orbit in the distant region beyond Neptune.

The key difference between planets and dwarf planets involves orbital clearing. Regular planets have strong enough gravity to clear their orbital paths. They sweep up or push away asteroids and other small objects. Dwarf planets share their orbital space with many other objects. Evidence shows that Pluto's orbit crosses paths with numerous icy bodies. This shared space prevents Pluto from meeting the planet definition. Scientists observe that dwarf planets can have moons just like regular planets. Pluto has five known moons, and Haumea has two.

In 2006, astronomers gathered in Prague to vote on planet definitions. They decided that Pluto no longer fit the criteria for a full planet. This decision created the dwarf planet category. The vote was controversial, and some scientists still debate the classification system. New Horizons spacecraft flew past Pluto in 2015. The mission revealed that Pluto has a complex surface with mountains and plains. Scientists may discover more dwarf planets as telescope technology improves. Researchers estimate that dozens or even hundreds may exist in the outer solar system.

Understanding dwarf planets helps scientists learn about solar system formation. These objects preserve information from when the solar system was young. They contain materials that have changed little over billions of years. Studying dwarf planets also helps us understand how gravity shapes celestial bodies. The classification system shows how scientific knowledge can change with new discoveries. Scientists continue to refine their understanding of what makes a planet.

Interesting Fact: Haumea is one of the strangest dwarf planets because it spins so fast that it has an elongated, football-like shape instead of being round like most planets.

According to the passage, what are the three criteria that define a dwarf planet?

It must orbit the Sun, be round, and have cleared its orbital pathIt must orbit the Sun, be round, but has not cleared its orbital pathIt must have moons, be round, and orbit beyond NeptuneIt must be smaller than Earth, have gravity, and orbit the Sun

Which dwarf planet is the only one located in the inner solar system?

PlutoErisCeresMakemake

What does the term 'orbital clearing' mean in the context of planet classification?

Making sure the planet has a clear view of the SunSweeping up or pushing away asteroids and other objects from the orbital pathRemoving moons from around a planetCreating a circular orbit instead of an elliptical one

Based on the passage, what can you infer about why Eris's discovery was important?

It proved that all dwarf planets have moonsIt showed that objects beyond Neptune cannot be planetsIt led scientists to reconsider Pluto's classification as a planetIt was the first dwarf planet ever discovered

What makes Haumea different from most other planets and dwarf planets?

It has no moonsIt has an elongated, football-like shape due to its fast rotationIt is the largest dwarf planetIt orbits closest to the Sun

If scientists discovered a new round object orbiting the Sun that shares its orbital space with many asteroids, how would it most likely be classified?

As a regular planetAs a moonAs a dwarf planetAs a star

Why do scientists study dwarf planets to learn about solar system formation?

Because they are the largest objects in the solar systemBecause they preserve materials that have changed little over billions of yearsBecause they were formed after all the planetsBecause they have the strongest gravity

What evidence from the New Horizons mission changed scientists' understanding of Pluto?

It showed that Pluto has five moonsIt proved that Pluto should be a planet againIt revealed that Pluto has a complex surface with mountains and plainsIt demonstrated that Pluto has cleared its orbit

True or False: All dwarf planets are located beyond Neptune in the outer solar system.

TrueFalse

True or False: The International Astronomical Union created the dwarf planet classification in 2006.

TrueFalse