Pluto

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Pluto : a dwarf planet occupying an orbit that crosses the orbit of Neptune — in 2006 the International Astronomical Union defined planet in such a way as to exclude Pluto, reclassifying it instead as a dwarf planet. — Merriam-Webster See also OneLook

Encyclopedia

Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It was the first object discovered in the Kuiper belt and remains the largest known body in that area. After Pluto was discovered in 1930, it was declared the ninth planet from the Sun. However, beginning in the 1990s, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt and the scattered disc, including the dwarf planet Eris, leading the International Astronomical Union (IAU) in 2006 to define the term planet formally—excluding Pluto and reclassifying it as a dwarf planet.

Pluto is the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris. Like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—one-sixth the mass of the Moon and one-third its volume. It has a moderately eccentric and inclined orbit, ranging from 30 to 49 astronomical units (4.5 to 7.3 billion kilometers; 2.8 to 4.6 billion miles) from the Sun. Therefore, Pluto periodically comes closer to the Sun than Neptune. Still, a stable orbital resonance with Neptune prevents them from colliding.

Pluto has five known moons: Charon (the largest, whose diameter is just over half that of Pluto), Styx, Nix, Kerberos, and Hydra. Pluto and Charon are sometimes considered a binary system because the barycenter of their orbits does not lie within either body. — Wikipedia

Pluto (Encyclopædia Britannica)

Pluto (COSMOS: The SAO Encyclopedia of Astronomy)

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Inspiration

TED-Ed (YouTube Channel)
TED-Ed (Official Website)

The Journey to Pluto, the Farthest World Ever Explored (Alan Stern, TED-Ed)
Chasing New Horizons: Inside the Epic First Mission to Pluto (Alan Stern and David Grinspoon)

NASA’s Eyes is a freely available suite of computer visualization applications created by the Visualization Technology Applications and Development Team at NASA’s Jet Propulsion Laboratory (JPL) to render scientifically accurate views of the planets studied by JPL missions. — Wikipedia

NASA New Horizons (YouTube Channel)
NASA New Horizons (Official Website)

Pluto (NASA’s Eyes on the Solar System, NASA’s JPL & Cal Tech)

Pluto (Astrum, YouTube Playlist)

Articles about Pluto (Big Think)

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Innovation

Science

The New Horizons spacecraft performed a flyby of Pluto on July 14, 2015, becoming the first and, to date, only spacecraft to do so. During its brief flyby, New Horizons made detailed measurements and observations of Pluto and its moons. In September 2016, astronomers announced that the reddish-brown cap of the north pole of Charon is composed of tholins, organic macromolecules that may be ingredients for the emergence of life, and produced from methane, nitrogen, and other gases released from the atmosphere of Pluto and transferred 19,000 km (12,000 mi) to the orbiting moon. — Wikipedia

NASA Video (YouTube Channel)
NASA (Official Website)

Solar System Exploration: Pluto (NASA Science)
Solar System Exploration: Pluto’s Moons (NASA Science)

New Horizons Mission (NASA)

NASA New Horizons (YouTube Channel)
NASA New Horizons (Official Website)

New Horizons: NASA’s Mission to Pluto and the Kuiper Belt (Johns Hopkins University Applied Physics Laboratory)

Pluto in a Minute (NASA New Horizons, YouTube Playlist)
The Real PlutoPhiles (NASA New Horizons, YouTube Playlist)

Pluto and the Developing Landscape of Our Solar System (International Astronomical Union)
Pluto (Minor Planet Center, International Astronomical Union)

Pluto, The Kuiper Belt’s Most Famous Dwarf Planet (Planetary Society)

Pluto (Mike Brown’s Planets)

Pluto (Eric Weisstein’s World of Astronomy, Wolfram Research)
Pluto (Wolfram Alpha)

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Preservation

History

Planet X, Pluto, and NASA New Horizons (The History Guy, YouTube Video)

History of Pluto’s Discovery (Lowell Observatory)
Clyde W. Tombaugh (New Mexico Museum of Space History)
Pluto (National Air and Space Museum)
Clyde Tombaugh (Encyclopædia Britannica)

Pluto: Exploration (NASA Science)

Library

DDC: 523.4922 Pluto (Library Thing)
Subject: Pluto (Library Thing)

Subject: Pluto (Open Library)

LCC: QB 701 Pluto (UPenn Online Books)

LCC: QB 701 Pluto (Library of Congress)
Subject: Pluto (Library of Congress)

Subject: Pluto (WorldCat)

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Participation

Education

Pluto – Level 1 (StarChild, Goddard Space Flight Center, NASA)
Pluto – Level 2 (StarChild, Goddard Space Flight Center, NASA)

All About Pluto (Space Place, NASA)
Pluto (Cosmos4Kids)

Small Solar System Bodies Learning Resources (National Air and Space Museum)
Dwarf Planets Learning Resources (National Air and Space Museum)

MERLOT: Multimedia Educational Resource for Learning and Online Teaching
OER Commons: Open Educational Resources

Community

Organization

Minor Planet Center (International Astronomical Union)
Asteroids & Remote Planets Section (British Astronomical Association)

News

Pluto (Nova Research Highlights, American Astronomical Society)
Pluto (EurekaAlert, AAAS)
Pluto (JSTOR)
Pluto (Astronomy Magazine)
Pluto (Science Daily)
Pluto (Phys.org)

Recent News from Phys.org …

Rubin Observatory reveals its first dwarf planet...
on October 27, 2026 at 10:30 pm
Scientists may add a new dwarf planet to the official roster of our solar system. The distant, icy body, provisionally dubbed 2026 ED138, orbits our system beyond Pluto. It was spotted earlier this month by a scientist combing through data from the Simonyi Survey Telescope at the NSF-DOE Vera C. Rubin Observatory.
Double debris disk orbiting a dead star hints at...
on October 27, 2026 at 10:00 pm
Astronomers using the European Southern Observatory's Very Large Telescope (ESO's VLT) have found a rare disk of debris around a dead star that provides a glimpse of what may happen to our solar system. Unlike in similar systems previously found, the debris—the leftovers of planets that once orbited the star—is organized in a double disk, the two parts separated by a clear gap. The disk appears to be shaped by two planetary bodies, one possibly as big as Pluto, that have survived the […]
Enigmatic Mercury will remain a puzzle until...
on October 19, 2026 at 1:20 pm
Mercury remains one of our solar system's most elusive and difficult planets to study. It's easier to send probes to the icy moons of Saturn or Jupiter, or even to Pluto, than to land on our innermost planet, Mercury.
Giant impact could have formed an intact moon...
on September 1, 2026 at 10:20 pm
New Southwest Research Institute (SwRI) modeling, conducted in collaboration with scientists at the University of Arizona, shows fundamental differences in how the moon may have formed from the giant impact that created the Earth–moon system. The new results used state-of-the-art computational techniques that factor in the material strength of the two colliding planets. These impact simulations could change how researchers understand moon formation and may help constrain the timing of the […]
Will new telescope Roman help reveal long-kept...
on August 28, 2026 at 11:40 am
On Sunday, Aug. 30, the Nancy Grace Roman Space Telescope is expected to launch from NASA's Kennedy Space Center in Florida. The observatory will join the Hubble Space Telescope, launched in 1990, and the James Webb Space Telescope, launched in 2021, in scanning the vastness of space and potentially finding answers to longstanding mysteries of the universe.