Pluto is the second-most massive known dwarf planet, after Eris. It is the largest object in the Kuiper belt and possibly the largest known trans-Neptunian object by volume. It is the tenth-most-massive known body directly orbiting the Sun. Like other Kuiper belt objects, Pluto is primarily made of rock and ice, and is relatively small- about 1Ú6 the mass of the Moon and 1Ú3 its volume.

It has a moderately eccentric and inclined orbit that takes it from 30 to 49 AU (4.4Đ7.4 billion km) from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune. However, an orbital resonance with Neptune prevents them from colliding.

In 2014, Pluto was 32.6 AU from the Sun. Light from the Sun takes about 5.5 hours to reach Pluto at its average distance (39.4 AU). Pluto was discovered in 1930 and was originally considered the ninth planet from the Sun. Its status as a planet fell into question following further study of it and the outer Solar System over the following 75 years. Starting in 1977 with the discovery of the minor planet Chiron, numerous icy objects with eccentric orbits were found.

The scattered disc object Eris, discovered in 2005, is 27% more massive than Pluto. The knowledge that Pluto is only one of several large icy bodies in the outer Solar System prompted the International Astronomical Union (IAU) to formally define the term "planet" in 2006, which excluded Pluto and reclassified it as a member of the new "dwarf planet" category (and specifically as a plutoid). Astronomers who oppose the exclusion assert that Pluto should remain classified as a planet and other dwarf planets, and even moons, should be added to the list of planets.

Pluto has five known moons: Charon (the largest, with a diameter 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. The IAU has not formalized a definition for binary dwarf planets, and Charon is officially classified as a moon of Pluto. Read more ....

Pluto in the News ...

Pluto 'has slushy ocean' below surface   BBC - November 17, 2016

Pluto may harbor a slushy water ocean beneath its most prominent surface feature, known as the "heart". This could explain why part of the heart-shaped region - called Sputnik Planitia - is locked in alignment with Pluto's largest moon Charon. A viscous ocean beneath the icy crust could have acted as a heavy, irregular mass that rolled Pluto over, so that Sputnik Planitia was facing the moon. The findings are based on data from Nasa's New Horizons spacecraft. The space probe flew by the dwarf planet in July 2015 and is now headed into the Kuiper Belt, an icy region of the Solar System beyond Neptune's orbit. Sputnik Planitia is a circular region in the heart's left "ventricle" and is aligned almost exactly opposite Charon. In addition, Pluto and Charon are tidally locked, which results in Pluto and Charon always showing the same face to each other.

  Pluto's 'Heart' Hints at Deep, Underground Ocean   Live Science - September 26, 2016

A new simulation of how Pluto got its "heart" suggests that the dwarf planet most likely has a deep ocean beneath its surface. Scientists have long suspected that Pluto has liquid water hidden underground. When NASA's New Horizons mission first set sail to the outskirts of the solar system, scientists were already planning to investigate whether the dwarf planet harbors water. When New Horizons flew past Pluto in July 2015 and beamed its observations back to Earth, scientists found evidence suggesting that Pluto had water at some point. However, they weren't sure whether Pluto's had an existing ocean, or if it had frozen solid over time.

Pluto is covered in a lot of frozen water   CNN - January 30, 2016

Talk about an endless winter: Pluto has way more frozen water than scientists originally thought. The dwarf planet is coated with a large amount of ice, according to a new map using previously collected data from NASA's New Horizons spacecraft.

Pluto: From Mountains to Plains   NASA - December 14, 2015

What caused the mysterious 'wormholes' on Pluto? Nasa baffled by pits and troughs hundreds of meters across and tens of meters deep   Daily Mail - October 19, 2015

Each of the pits and troughs are typically hundreds of meters across and tens of meters deep. Were spotted in the area, informally known as Sputnik Planum. Believed they may have been caused by volatile ices such as solid nitrogen

New Horizons: Probe captures Pluto's blue hazes   BBC - October 8, 2015

The New Horizons mission has returned its first color image of Pluto's atmospheric hazes and shows them to have a blue tinge. Like Earth, the dwarf has a predominantly nitrogen atmosphere (albeit much more sparse). But it is the interaction of this nitrogen with the Sun's ultraviolet light, in presence of another atmospheric constituent, methane, that is able to create the chunky haze particles.

A Plutonian Landscape   NASA - September 18, 2015

This shadowy landscape of majestic mountains and icy plains stretches toward the horizon of a small, distant world. It was captured from a range of about 18,000 kilometers when New Horizons looked back toward Pluto, 15 minutes after the spacecraft's closest approach on July 14. The dramatic, low-angle, near-twilight scene follows rugged mountains still popularly known as Norgay Montes from foreground left, and Hillary Montes along the horizon, giving way to smooth Sputnik Planum at right. Layers of Pluto's tenuous atmosphere are also revealed in the backlit view. With a strangely familiar appearance, the frigid terrain likely includes ices of nitrogen and carbon monoxide with water-ice mountains rising up to 3,500 meters (11,000 feet). That's comparable in height to the majestic mountains of planet Earth. This Plutonian landscape is 380 kilometers (230 miles) across.

Latest images reveal Pluto's hazy horizon   BBC - September 17, 2015

Fresh images from Nasa's New Horizons spacecraft have captured a low-lying haze clinging to the surface of Pluto.

New Horizons reveals more mountains in Pluto's heart   BBC - July 22, 2015

The latest images from the New Horizons spacecraft have revealed another range of ice mountains on Pluto. The frozen peaks were found on the lower-left edge of the dwarf world's "heart" and are 1-1.5km-high.

From APOD Saturday July 18, 2015

  New Horizons probe zooms into Pluto's plains   BBC - July 17, 2015

The American space agency's New Horizons probe has returned further images of Pluto that include a view of the dwarf planet's strange icy plains. A region, which has been named after the Soviet Sputnik satellite, displays a flat terrain broken up into polygons. At the edges of these 20-30km-wide features are troughs filled with dark material and even small mounds.

  Pluto-Charon Fly-by: High Resolution Imagery Revealed By NASA - July 15, 2015

New Horizons: Images reveal ice mountains on Pluto   BBC - July 15, 2015

Pluto has mountains made of ice that are as high as those in the Rockies, images from the New Horizons probe reveal. They also show signs of geological activity on Pluto and its moon Charon.

  Pluto Flyby 'Phone-Home' Call from New Horizons - July 14, 2015

  New Horizons Probe Finds Out Pluto's Bigger (and Icier) Than We Thought   NBC - July 13, 2015

New Horizons: 5 Things Pluto Flyby Could Reveal About Planet Earth   Live Science - July 13, 2015
How Earth formed
Where Earth's water came from
How life began on Earth
Earth's atmospheric structure
How the sun affects Earth

Pluto's hidden ocean   PhysOrg - November 25, 2011
When NASA's New Horizons cruises by Pluto in 2015, the images it captures could help astronomers determine if an ocean is hiding under the frigid surface, opening the door to new possibilities for liquid water to exist on other bodies in the solar system. New research has not only concluded such an ocean is likely, but also has highlighted features the spacecraft could identify that could help confirm an oceanŐs existence.

'Non-planet' Pluto gets new class - "Plutoid"   BBC - June 14, 2008
"Plutoid" is the word of the moment for astronomers. It is the new classification that has been sanctioned for the object that was formerly known as the "ninth planet". It is nearly two years since the International Astronomical Union (IAU) stripped Pluto of its former status as a "proper" planet. Now an IAU committee, meeting in Oslo, has suggested that small, nearly spherical objects orbiting beyond Neptune should carry the "plutoid" tag. As astronomy's official nomenclature organization, the IAU must approve all new names and classifications.

Astronomers Relegate Pluto to Dwarf Status   Scientific American - August 25, 2006
After a week of contentious public and private debate, a small cluster of astronomers has voted to demote Pluto from its planetary status. Rejecting an expansive definition proposed by a special committee, the astronomers of the International Astronomical Union (IAU) defined a planet as: a celestial body that orbits around the sun; has sufficient mass to become round; and has "cleared the neighborhood around its orbit." On the strength of puny Pluto's inability to dominate nearby Neptune, whose orbit it crosses, as well as to clear out the Kuiper belt of many Pluto-size objects, it fails to qualify as a planet under the new definition.

Pluto's new moons named Hydra and Nix   MSNBC - June 21, 2006

The International Astronomical Union has officially christened Pluto's two newest moons Nix and Hydra. The tiny satellites were discovered by the Hubble Space Telescope last May and are believed to have been formed from the same giant impact that carved out Charon, Pluto's larger satellite, discovered in 1978. The names were proposed this spring by the team that discovered the satellites. Before the satellites received their official names, they were called P1 and P2. In Greek mythology, Nyx was the goddess of the night and the mother of Charon, the boatsman who ferried souls across the River Styx into the underworld ruled by Pluto. The IAU changed the spelling to "Nix" after the Egyptian spelling of the goddess, to avoid confusion with two asteroids that had already been named "Nyx." The outermost of Pluto's two new satellites is named after Hydra, the nine-headed mythological serpent that guarded Pluto's realm.

Pluto moon 'has no atmosphere'   BBC - January 7, 2006
A rare astronomical event has allowed scientists to show that Pluto's moon - known as Charon - has no atmosphere. This could dismiss claims Charon is a planet twinned with Pluto and provide further insight into their formation. Two groups of scientists made observations of the moon as it eclipsed a distant star in the July of 2005. The size of any atmosphere around Charon was figured out by observing how gradually the star disappeared and reappeared during the eclipse. When Charon passed in front of a star - in an occultation event - astronomers knew it would either cut the light off gradually or very quickly. If the moon had no atmosphere then the light would be cut off sharply. However an atmosphere would cause a gradual cut off.

Two new moons found around Pluto   BBC - November 1, 2005
The Hubble Space Telescope has spotted two possible new moons around Pluto, the ninth planet in the Solar System. If confirmed, it would bring Pluto's tally of satellites to three; Charon, the only known moon of Pluto, was discovered by astronomers in 1978. Confirmation of two new moons would shed light on the evolution of the Kuiper Belt, the vast region containing icy objects beyond Neptune's orbit. All the candidate moons seem to orbit Pluto in an anti-clockwise direction. The candidate moons, given the provisional names S/2005 P1 and S/2005 P2, are between 45 and 160km (30 and 100 miles) across. By comparison, Charon's diameter is about 1,200km (745 miles). Observations suggest they orbit Pluto at at least twice the distance Charon does. P2 stays about 49,000km (30,000 miles) from the planet; P1 lies even further away at 65,000km (40,000 miles)

Pluto in Mythology

Egyptian Mythology

Pluto as Anubis the Egyptian god of the Dead.

Later he was superseded in that role by Osiris.

Roman Mythology

In Roman mythology, Pluto is the god of the underworld, and Charon is the ferryman across the river Styx, the moat into Pluto's realm. Though old and gray, Charon is strong and sturdy. Dressed in a short cloak, he chooses his passengers from among the multitudes of the dead that crowd the shore. Only those properly buried in the world above are chosen, and then only if they have the fare - a silver coin placed in the mouth of the corpse before burial.

Pluto, in Roman mythology, is the husband of Persephone.

Pluto, the lord of the underworld, represents the body intelligence of man; and the rape of Persephone is symbolic of the divine nature assaulted and defiled by the animal soul and dragged downward into the somber darkness of Hades, which is here used as a synonym for the material, or objective, sphere of consciousness.

In his Disquisitions upon the Painted Greek Vases, James Christie presents Meursius' version of the occurrences taking place during the nine days required for the enactment of the Greater Eleusinian Rites. The first day was that of general meeting, during which those to be initiated were questioned concerning their several qualifications.

The second day was spent in a procession to the sea, possibly for the submerging of an image of the presiding goddess. The third day was opened by the sacrifice of a mullet. On the fourth day the mystic basket containing certain sacred symbols was brought to Eleusis, accompainied by a number of female devotees carrying smaller baskets. On the evening of the fifth day there was a torch race, on the sixth a procession led by a statue of Iacchus, and on the seventh an athletic contest.

The eighth day was devoted to a repetition of the previous ceremonial for the benefit of any who might have been prevented from attending sooner. The ninth and last day was devoted to the deepest philosophical issues of the Eleusinia, during which an urn or jar - the symbol of Bacchus - was exhibited as an emblem of supreme importance.

Greek Mythology

Pluto in Greek mythology was Hades.

He was the son of the Titans Cronus (Saturn) and Rhea
and the brother of Zeus (Jupiter) and Poseidon (Neptune).

The Latin counterpart of the Greek god Hades, Pluto assisted his two brothers, Jupiter (Zeus) and Neptune, in overthrowing their father, Saturn.

The name Pluto means "rich one," and the Romans derived Dis (from dives, "rich"), their god of the dead, from Pluto. Pluto or Pluton or Hades was a god of both death and fertility or abundance.

In dividing the world among them, Jupiter chose the Earth and the heavens as his realm, Neptune became the ruler of the sea, and Pluto received as his kingdom the lower world, in which he ruled over the shades of the dead.

He was originally considered a fierce and unyielding god, deaf to prayers and unappeased by sacrifices. In later cults and popular belief the milder and more beneficent aspects of the god were stressed.

Believed to be the bestower of the blessings hidden in the Earth, such as mineral wealth and crops, Pluto was also known as Dis or Orcus, the giver of wealth.

Pluto's realm, the house of Hades is usually located beneath the Earth, though sometimes in the west.


Pluto represents transformation. Pluto is the planet of profound change, starting deep within us and moving toward the surface. It often touches upon the most sensitive psychological areas inside us. Once touched, we have no choice but to change and grow. Pluto is about death and rebirth, the transformation that comes from letting go of that which is unessential so that we can get to the core of things.


Pluto rules Scorpio