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 …

Liquid nitrogen may have recently flowed across...
on August 6, 2026 at 1:00 pm
A new study led by Southwest Research Institute (SwRI) provides evidence that liquid nitrogen is rising to Pluto's surface through cracks at the northern edge of Sputnik Planitia, part of the massive heart-shaped glacier on the dwarf planet's surface. This is the first evidence of liquid flow occurring recently on Pluto. The study is based on data from NASA's New Horizons spacecraft and led by SwRI Associate Vice President Dr. Alan Stern, the principal investigator of the New Horizons mission.
Pluto's hazy atmosphere may be collapsing as it...
on August 3, 2026 at 2:40 pm
Pluto is on an icy march away from the sun. In 2114, it will turn back, but until then, its elliptical orbit will carry it to colder and darker parts of the outer solar system. This is Pluto's first time entering the outer solar system since its 1930 discovery, and along this journey, its atmosphere could slowly freeze out.
Neptune's inner moons may be shattered remains of...
on July 30, 2026 at 2:00 pm
In 1989, the Voyager 2 mission discovered six new moons orbiting Neptune, including five tiny ones that orbit just outside the planet's main rings. Because of their small sizes and locations, these satellites have been difficult to study from Earth. Now, using NASA's James Webb Space Telescope (JWST), a team of Caltech researchers has observed Neptune's rings and three of those moons—Larissa, Galatea and Proteus—and found that their composition is unique among outer solar system bodies.
The spin of Pluto's moon, Charon, may be slowing...
on July 14, 2026 at 5:38 pm
Evidence of the slowing of Charon's spin period (despinning) is recorded in tectonic features on the surface of Pluto's icy moon, according to a modeling study published in Nature Communications. The findings offer insights into the early thermal evolution of Charon and other icy satellites in the outer solar system.
Six massive landslides discovered on icy Pluto
on July 13, 2026 at 7:30 pm
Scientists have detected evidence of landslides on Pluto for the first time. A paper published in the journal Icarus reports that images taken by the New Horizons spacecraft during a flyby revealed six large landslides in three impact craters.