Pluto

Introduction & Top Questions
Basic astronomical data
The atmosphere
The surface and interior
Pluto’s moons
Discoveries of Pluto and its moons
Origin of Pluto and its moons
Pluto’s status as a solar system member

References & Edit History Related Topics

Images & Videos

At a Glance

Pluto summary

Quizzes

View of the Andromeda Galaxy (Messier 31, M31).

Astronomy and Space Quiz

The orbits of the planets and other elements of the solar system, including asteroids, Kuiper belt, Oort cloud, comet

Space Odyssey

Saturn. Saturn and its rings. Second largest planet of the solar system. Space Art

Planets and the Earth’s Moon

Nicolaus Copernicus. Nicolas Copernicus (1473-1543) Polish astronomer. In 1543 he published, forward proof of a Heliocentric (sun centered) universe. Coloured stipple engraving published London 1802. De revolutionibus orbium coelestium libri vi.

All About Astronomy

Scientists combine four images from New Horizons Long Range Reconnaissance Imager (LORRI) with Ralph instrument infrared images to create this false color global view of dwarf planet Pluto on July 14, 2015, 280,000 miles away from the spacecraft.

Pluto

Related Questions

Does Pluto have an atmosphere?
How big is Pluto compared with Earth’s Moon?
How did Clyde Tombaugh find Pluto?
How does Charon’s surface differ from Pluto’s surface?
How does the brightness of Tombaugh Regio differ from that of Cthulhu Regio?
How far is Pluto from the Sun?
How is Pluto connected to the Kuiper belt?
How is Pluto’s orbit different from the orbits of the eight planets?
How is a dwarf planet different from a planet?
How long does Pluto take to orbit the Sun?
How long is a day on Pluto?
How many moons does Pluto have?
How might a giant collision have formed Pluto and its moons?
How much sunlight does Pluto receive compared with Earth?
How was Pluto’s atmosphere discovered in 1988?
What are the names of Pluto’s five moons?
What are tholins on Pluto?
What causes the dark color of Cthulhu Regio on Pluto?
What did New Horizons discover about Pluto’s haze layers?
What did New Horizons discover about Pluto’s possible underground ocean?
What did New Horizons discover about Pluto’s surface?
What does Pluto’s 3:2 orbital resonance with Neptune mean?
What is Sputnik Planitia?
What tool did Clyde Tombaugh use to compare photographs of the sky?
When did the International Astronomical Union reclassify Pluto?
When did the New Horizons spacecraft fly past Pluto?
When were Kerberos and Styx discovered?
When were Nix and Hydra discovered?
Which International Astronomical Union rule does Pluto not meet for planet status?
Which Roman god was Pluto named after?
Which gases make up Pluto’s atmosphere?
Which of Pluto’s moons is the largest?
Who discovered Charon?
Who discovered Pluto in 1930?
Who suggested the name Pluto for the dwarf planet?
Why are Pluto and Charon sometimes called a double system?
Why can Pluto and Neptune never collide even when Pluto crosses Neptune’s orbit?
Why did astronomers search for Planet X beyond Neptune?
Why do Pluto’s smaller moons spin rapidly and chaotically?
Why does Charon always show the same side to Pluto?
Why does Pluto sometimes become closer to the Sun than Neptune?
Why does Pluto’s atmosphere change as its distance from the Sun changes?
Why does the Sun rise in the west on Pluto?
Why does the lack of craters on Sputnik Planitia suggest geologic activity on Pluto?
Why is Charon visible from only one hemisphere of Pluto?
Why is Pluto also classified as a plutoid?
Why is Pluto’s surface so cold?
Why is Tombaugh Regio called Pluto’s heart-shaped region?
Why is nitrogen ice important on Pluto’s surface?
Why was Pluto’s discovery not actually predicted by disturbances in Uranus’s orbit?
Why was the name Pluto chosen for the newly discovered object?
Is Pluto a planet?
Is Pluto’s orbit circular or eccentric?
Does Pluto have any moons?

Science Astronomy

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External Websites

International Astronomical Unit - Pluto and the Developing Landscape of Our Solar System
University of Central Florida Pressbooks - Pluto and Charon
NASA Science - Pluto
NPR - Pluto isnÂ’t a planet Â— but it gives us clues for how the solar system formed
National Center for Biotechnology Information - PubMed Central - Pluto: dazzling, dynamic, and so not dead
The Planets - Pluto Facts
NASA - What is Pluto?
Open Library Publishing Platform - Fanshawe College Astronomy - Pluto and Charon
Space.com - Pluto: Everything you need to know about the dwarf planet
The Nine Planets - Pluto Facts

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

Pluto - Children's Encyclopedia (Ages 8-11)
Pluto - Student Encyclopedia (Ages 11 and up)

Pluto

dwarf planet

Written by

Tobias Chant Owen

Professor of Astronomy, University of Hawaii at Manoa, Honolulu. Coauthor of The Planetary System; The Search for Life in the Universe; and numerous research articles.

Tobias Chant Owen

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 13, 2026 •History

Pluto, large, distant member of the solar system that formerly was regarded as the outermost and smallest planet. It also was considered the most recently discovered planet, having been found in 1930. In August 2006 the International Astronomical Union (IAU), the organization charged by the scientific community with classifying astronomical objects, voted to remove Pluto from the list of planets and give it the new classification of dwarf planet. The change reflects astronomers’ realization that...

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