Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in
the Kuiper belt, a ring of bodies beyond Neptune. It was the first
Kuiper belt object to be discovered.
Pluto was discovered by
Clyde Tombaugh in 1930 and was originally
considered to be the ninth planet from the Sun. After 1992, its status
as a planet was questioned following the discovery of several objects
of similar size in the Kuiper belt. In 2005, Eris, a dwarf planet in
the scattered disc which is 27% more massive than Pluto, was
discovered. This led the
International Astronomical Union
International Astronomical Union (IAU) to
define the term "planet" formally in 2006, during their 26th General
Assembly. That definition excluded
Pluto and reclassified it as a
Pluto is the largest and second-most-massive known dwarf planet in the
Solar System, and 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
Kuiper belt objects,
Pluto is primarily made of ice and rock and
is relatively small—about one-sixth the mass of the
one-third its volume. It has a moderately eccentric and inclined orbit
during which it ranges from 30 to 49 astronomical units or AU
(4.4–7.4 billion km) from the Sun. This means that Pluto
periodically comes closer to the
Sun than Neptune, but a stable
orbital resonance with
Neptune prevents them from colliding. Light
Sun takes about 5.5 hours to reach
Pluto at its average
distance (39.5 AU).
Pluto has five known moons: Charon (the largest, with a diameter just
over half that of Pluto), Styx, Nix, Kerberos, and Hydra.
Charon are sometimes considered a binary system because the barycenter
of their orbits does not lie within either body.
On July 14, 2015, the
New Horizons spacecraft became the first
spacecraft to fly by Pluto. 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
Pluto and transferred about 19,000 km
(12,000 mi) to the orbiting moon.
Planet X disproved
1.4.1 IAU classification
2.1 Relationship with Neptune
2.1.1 Other factors
4.2 Internal structure
Mass and size
9 Observation and exploration
10 See also
13 Further reading
14 External links
Further information: Planets beyond Neptune
Discovery photographs of Pluto
Clyde Tombaugh, in Kansas
In the 1840s,
Urbain Le Verrier
Urbain Le Verrier used Newtonian mechanics to predict
the position of the then-undiscovered planet
Neptune after analyzing
perturbations in the orbit of Uranus. Subsequent observations of
Neptune in the late 19th century led astronomers to speculate that
Uranus's orbit was being disturbed by another planet besides Neptune.
In 1906, Percival Lowell—a wealthy Bostonian who had founded Lowell
Observatory in Flagstaff, Arizona, in 1894—started an extensive
project in search of a possible ninth planet, which he termed "Planet
X". By 1909, Lowell and William H. Pickering had suggested several
possible celestial coordinates for such a planet. Lowell and his
observatory conducted his search until his death in 1916, but to no
avail. Unknown to Lowell, his surveys had captured two faint images of
Pluto on March 19 and April 7, 1915, but they were not recognized for
what they were. There are fourteen other known precovery
observations, with the oldest made by the
Yerkes Observatory on August
Percival's widow, Constance Lowell, entered into a ten-year legal
battle with the
Lowell Observatory over her husband's legacy, and the
Planet X did not resume until 1929. Vesto Melvin
Slipher, the observatory director, gave the job of locating
to 23-year-old Clyde Tombaugh, who had just arrived at the observatory
after Slipher had been impressed by a sample of his astronomical
Tombaugh's task was to systematically image the night sky in pairs of
photographs, then examine each pair and determine whether any objects
had shifted position. Using a blink comparator, he rapidly shifted
back and forth between views of each of the plates to create the
illusion of movement of any objects that had changed position or
appearance between photographs. On February 18, 1930, after nearly a
year of searching, Tombaugh discovered a possible moving object on
photographic plates taken on January 23 and 29. A lesser-quality
photograph taken on January 21 helped confirm the movement. After
the observatory obtained further confirmatory photographs, news of the
discovery was telegraphed to the
Harvard College Observatory
Harvard College Observatory on March
The discovery made headlines around the globe. Lowell Observatory,
which had the right to name the new object, received more than 1,000
suggestions from all over the world, ranging from Atlas to Zymal.
Tombaugh urged Slipher to suggest a name for the new object quickly
before someone else did. Constance Lowell proposed Zeus, then
Percival and finally Constance. These suggestions were
The name Pluto, after the god of the underworld, was proposed by
Venetia Burney (1918–2009), an eleven-year-old schoolgirl in Oxford,
England, who was interested in classical mythology. She suggested
it in a conversation with her grandfather Falconer Madan, a former
librarian at the University of Oxford's Bodleian Library, who passed
the name to astronomy professor Herbert Hall Turner, who cabled it to
colleagues in the United States.
Each member of the
Lowell Observatory was allowed to vote on a
short-list of three potential names:
Minerva (which was already the
name for an asteroid),
Cronus (which had lost reputation through being
proposed by the unpopular astronomer Thomas Jefferson Jackson See),
Pluto received every vote. The name was announced on
May 1, 1930. Upon the announcement, Madan gave Venetia £5
(equivalent to 300 GBP, or 450
USD in 2014) as a reward.
The final choice of name was helped in part by the fact that the first
two letters of
Pluto are the initials of Percival Lowell. Pluto's
astronomical symbol (,
Unicode U+2647, ♇) was then created as a
monogram constructed from the letters "PL". Pluto's astrological
symbol resembles that of
Neptune (), but has a circle in place of the
middle prong of the trident ().
The name was soon embraced by wider culture. In 1930,
Walt Disney was
apparently inspired by it when he introduced for
Mickey Mouse a canine
companion named Pluto, although Disney animator
Ben Sharpsteen could
not confirm why the name was given. In 1941, Glenn T. Seaborg
named the newly created element plutonium after Pluto, in keeping with
the tradition of naming elements after newly discovered planets,
following uranium, which was named after Uranus, and neptunium, which
was named after Neptune.
Most languages use the name "Pluto" in various transliterations.[h] In
Houei Nojiri suggested the translation Meiōsei (冥王星,
"Star of the King (God) of the Underworld"), and this was borrowed
into Chinese, Korean, and Vietnamese (which instead uses "Sao Diêm
Vương", which was derived from the Chinese term 閻王 (Yánwáng),
as "minh" is a homophone for the Sino-Vietnamese words for "dark"
(冥) and "bright" (明)). Some Indian languages use the
name Pluto, but others, such as Hindi, use the name of Yama, the God
of Death in
Hindu and Buddhist mythology. Polynesian languages
also tend to use the indigenous god of the underworld, as in Maori
Planet X disproved
Pluto was found, its faintness and lack of a resolvable disc cast
doubt on the idea that it was Lowell's
Planet X. Estimates of
Pluto's mass were revised downward throughout the 20th century.
Mass estimates for Pluto
Lowell (prediction for
Nicholson & Mayall
0.1 (1/10) Earth
0.01 (1/100) Earth
Cruikshank, Pilcher, & Morrison
0.0015 (1/650) Earth
Christy & Harrington
0.00218 (1/459) Earth
Buie et al.
Astronomers initially calculated its mass based on its presumed effect
Neptune and Uranus. In 1931,
Pluto was calculated to be roughly the
mass of Earth, with further calculations in 1948 bringing the mass
down to roughly that of Mars. In 1976, Dale Cruikshank, Carl
Pilcher and David Morrison of the
University of Hawaii
University of Hawaii calculated
Pluto's albedo for the first time, finding that it matched that for
methane ice; this meant
Pluto had to be exceptionally luminous for its
size and therefore could not be more than 1 percent the mass of
Earth. (Pluto's albedo is 1.4–1.9 times that of Earth.)
In 1978, the discovery of Pluto's moon Charon allowed the measurement
of Pluto's mass for the first time: roughly 0.2% that of Earth, and
far too small to account for the discrepancies in the orbit of Uranus.
Subsequent searches for an alternative
Planet X, notably by Robert
Sutton Harrington, failed. In 1992, Myles Standish used data from
Voyager 2's flyby of
Neptune in 1989, which had revised the estimates
of Neptune's mass downward by 0.5%—an amount comparable to the mass
of Mars—to recalculate its gravitational effect on Uranus. With the
new figures added in, the discrepancies, and with them the need for a
Planet X, vanished. Today, the majority of scientists agree that
Planet X, as Lowell defined it, does not exist. Lowell had made a
Planet X's orbit and position in 1915 that was fairly
close to Pluto's actual orbit and its position at that time; Ernest W.
Brown concluded soon after Pluto's discovery that this was a
coincidence, a view still held today.
Further information: Definition of planet
Artistic comparison of Pluto, Eris, Makemake, Haumea, Sedna, 2002 MS4,
2007 OR10, Quaoar, Salacia, Orcus, and
Earth along with the Moon.
From 1992 onward, many bodies were discovered orbiting in the same
volume as Pluto, showing that
Pluto is part of a population of objects
called the Kuiper belt. This made its official status as a planet
controversial, with many questioning whether
Pluto should be
considered together with or separately from its surrounding
population. Museum and planetarium directors occasionally created
controversy by omitting
Pluto from planetary models of the Solar
Hayden Planetarium reopened—in February 2000, after
renovation—with a model of only eight planets, which made headlines
almost a year later.
As objects increasingly closer in size to
Pluto were discovered in the
region, it was argued that
Pluto should be reclassified as one of the
Kuiper belt objects, just as Ceres, Pallas, Juno and Vesta lost their
planet status after the discovery of many other asteroids. On July 29,
2005, astronomers at
Caltech announced the discovery of a new
trans-Neptunian object, Eris, which was substantially more massive
Pluto and the most massive object discovered in the Solar System
since Triton in 1846. Its discoverers and the press initially called
it the tenth planet, although there was no official consensus at the
time on whether to call it a planet. Others in the astronomical
community considered the discovery the strongest argument for
Pluto as a minor planet.
Main article: IAU definition of planet
The debate came to a head in August 2006, with an IAU resolution that
created an official definition for the term "planet". According to
this resolution, there are three conditions for an object in the Solar
System to be considered a planet:
The object must be in orbit around the Sun.
The object must be massive enough to be rounded by its own gravity.
More specifically, its own gravity should pull it into a shape defined
by hydrostatic equilibrium.
It must have cleared the neighborhood around its orbit.
Pluto fails to meet the third condition. Its mass is substantially
less than the combined mass of the other objects in its orbit: 0.07
times, in contrast to Earth, which is 1.7 million times the remaining
mass in its orbit. The IAU further decided that bodies that,
like Pluto, meet criteria 1 and 2, but do not meet criterion 3 would
be called dwarf planets. In September 2006, the IAU included Pluto,
and Eris and its moon Dysnomia, in their Minor
giving them the official minor planet designations "(134340) Pluto",
"(136199) Eris", and "(136199) Eris I Dysnomia". Had
included upon its discovery in 1930, it would have likely been
designated 1164, following 1163 Saga, which was discovered a month
There has been some resistance within the astronomical community
toward the reclassification. Alan Stern, principal
investigator with NASA's
New Horizons mission to Pluto, derided the
IAU resolution, stating that "the definition stinks, for technical
reasons". Stern contended that, by the terms of the new
definition, Earth, Mars, Jupiter, and Neptune, all of which share
their orbits with asteroids, would be excluded. He argued that all
big spherical moons, including the Moon, should likewise be considered
planets. He also stated that because less than five percent of
astronomers voted for it, the decision was not representative of the
entire astronomical community. Marc W. Buie, then at the Lowell
Observatory petitioned against the definition. Others have
supported the IAU. Mike Brown, the astronomer who discovered Eris,
said "through this whole crazy circus-like procedure, somehow the
right answer was stumbled on. It's been a long time coming. Science is
self-correcting eventually, even when strong emotions are
Public reception to the IAU decision was mixed. Many accepted the
reclassification, but some sought to overturn the decision with online
petitions urging the IAU to consider reinstatement. A resolution
introduced by some members of the California State Assembly
facetiously called the IAU decision a "scientific heresy". The New
Mexico House of Representatives passed a resolution in honor of
Tombaugh, a longtime resident of that state, that declared that Pluto
will always be considered a planet while in New Mexican skies and that
March 13, 2007, was
Planet Day. The Illinois Senate
passed a similar resolution in 2009, on the basis that Clyde Tombaugh,
the discoverer of Pluto, was born in Illinois. The resolution asserted
Pluto was "unfairly downgraded to a 'dwarf' planet" by the
IAU." Some members of the public have also rejected the change,
citing the disagreement within the scientific community on the issue,
or for sentimental reasons, maintaining that they have always known
Pluto as a planet and will continue to do so regardless of the IAU
In 2006, in its 17th annual words-of-the-year vote, the American
Dialect Society voted plutoed as the word of the year. To "pluto" is
to "demote or devalue someone or something".
Researchers on both sides of the debate gathered in August 2008, at
the Johns Hopkins University
Applied Physics Laboratory for a
conference that included back-to-back talks on the current IAU
definition of a planet. Entitled "The Great
the conference published a post-conference press release indicating
that scientists could not come to a consensus about the definition of
planet. In June 2008, the IAU had announced in a press release
that the term "plutoid" would henceforth be used to refer to
other objects that have an orbital semi-major axis greater than that
Neptune and enough mass to be of near-spherical shape.
Pluto's motion 1900-2048
Pluto was discovered in 1930 near the star δ Geminorum, and merely
coincidentally crossing the ecliptic at this time of discovery. Pluto
moves about 7 degrees east per decade with small apparent retrograde
motion as seen from Earth.
Pluto was closer to the
Sun than Neptune
between 1979 and 1999.
Pluto's orbital period is presently about 248 years. Its orbital
characteristics are substantially different from those of the planets,
which follow nearly circular orbits around the
Sun close to a flat
reference plane called the ecliptic. In contrast, Pluto's orbit is
moderately inclined relative to the ecliptic (over 17°) and
moderately eccentric (elliptical). This eccentricity means a small
region of Pluto's orbit lies closer to the
Sun than Neptune's. The
Pluto–Charon barycenter came to perihelion on September 5,
1989,[i] and was last closer to the
February 7, 1979, and February 11, 1999.
In the long term, Pluto's orbit is chaotic. Computer simulations can
be used to predict its position for several million years (both
forward and backward in time), but after intervals longer than the
Lyapunov time of 10–20 million years, calculations become
Pluto is sensitive to immeasurably small details of the
Solar System, hard-to-predict factors that will gradually change
Pluto's position in its orbit.
The semi-major axis of Pluto's orbit varies between about 39.3 and
39.6 au with a period of about 19,951 years, corresponding to an
orbital period varying between 246 and 249 years. The semi-major axis
and period are presently getting longer.
Orbit of Pluto—ecliptic view. This "side view" of Pluto's orbit (in
red) shows its large inclination to the ecliptic.
Orbit of Pluto—polar view. This "view from above" shows how Pluto's
orbit (in red) is less circular than Neptune's (in blue), and how
Pluto is sometimes closer to the
Sun than Neptune. The darker halves
of both orbits show where they pass below the plane of the ecliptic.
Relationship with Neptune
Despite Pluto's orbit appearing to cross that of
Neptune when viewed
from directly above, the two objects' orbits are aligned so that they
can never collide or even approach closely.
The two orbits do not intersect. When
Pluto is closest to the Sun, and
hence closest to Neptune's orbit as viewed from above, it is also the
farthest above Neptune's path. Pluto's orbit passes about 8 AU above
that of Neptune, preventing a collision.
This alone is not enough to protect Pluto; perturbations from the
planets (especially Neptune) could alter Pluto's orbit (such as its
orbital precession) over millions of years so that a collision could
be possible. However,
Pluto is also protected by its 2:3 orbital
resonance with Neptune: for every two orbits that
Pluto makes around
Neptune makes three. Each cycle lasts about 495 years. This
pattern is such that, in each 495-year cycle, the first time
Neptune is over 50° behind Pluto. By Pluto's second
Neptune will have completed a further one and a half of
its own orbits, and so will be nearly 130° ahead of Pluto.
Neptune's minimum separation is over 17 AU, which is greater than
Pluto's minimum separation from
Uranus (11 AU). The minimum
Neptune actually occurs near the time of
The 2:3 resonance between the two bodies is highly stable, and has
been preserved over millions of years. This prevents their orbits
from changing relative to one another, and so the two bodies can never
pass near each other. Even if Pluto's orbit were not inclined, the two
bodies could never collide. The long term stability of the
mean-motion resonance is due to phase protection. If Pluto's period is
slightly shorter than 3/2 of
Neptune its orbit relative to Neptune
will drift, causing it to make closer approaches behind Neptune's
orbit. The strong gravitational pull between the two causes angular
momentum to be transferred to Pluto, at Neptune's expense. This moves
Pluto into a slightly larger orbit, where it travels slightly more
slowly, according to Kepler's third law. After many such repetitions,
Pluto is sufficiently slowed, and
Neptune sufficiently sped up, that
Pluto orbit relative to
Neptune drifts in the opposite direction until
the process is reversed. The whole process takes about 20,000 years to
Numerical studies have shown that over millions of years, the general
nature of the alignment between the orbits of
not change. There are several other resonances and
interactions that enhance Pluto's stability. These arise principally
from two additional mechanisms (besides the 2:3 mean-motion
First, Pluto's argument of perihelion, the angle between the point
where it crosses the ecliptic and the point where it is closest to the
Sun, librates around 90°. This means that when
Pluto is closest
to the Sun, it is at its farthest above the plane of the Solar System,
preventing encounters with Neptune. This is a consequence of the Kozai
mechanism, which relates the eccentricity of an orbit to its
inclination to a larger perturbing body—in this case Neptune.
Relative to Neptune, the amplitude of libration is 38°, and so the
angular separation of Pluto's perihelion to the orbit of
always greater than 52° (90°–38°). The closest such angular
separation occurs every 10,000 years.
Second, the longitudes of ascending nodes of the two bodies—the
points where they cross the ecliptic—are in near-resonance with the
above libration. When the two longitudes are the same—that is, when
one could draw a straight line through both nodes and the
Sun—Pluto's perihelion lies exactly at 90°, and hence it comes
closest to the
Sun when it is highest above Neptune's orbit. This is
known as the 1:1 superresonance. All the Jovian planets, particularly
Jupiter, play a role in the creation of the superresonance.
In 2012, it was hypothesized that
15810 Arawn could be a
quasi-satellite of Pluto, a specific type of co-orbital
configuration. According to the hypothesis, the object would be a
Pluto for about 350,000 years out of every
two-million-year period. This hypothesis was disproven in
2016, when more-accurate observations of the position of Arawn were
made by New Horizons.
Pluto's rotation period, its day, is equal to 6.39
Pluto rotates on its "side" in its orbital plane, with an
axial tilt of 120°, and so its seasonal variation is extreme; at its
solstices, one-fourth of its surface is in continuous daylight,
whereas another fourth is in continuous darkness. The reason for
this unusual orientation has been debated. Research from University of
Arizona has suggested that it may be due to the way that a body's spin
will always adjust to minimise energy. This could mean a body
reorienting itself to put extraneous mass near the equator and regions
lacking mass tend towards the poles. This is called polar wander.
According to a paper released from the University of Arizona, this
could be caused by masses of frozen nitrogen building up in shadowed
areas of the dwarf planet. These masses would cause the body to
reorient itself, leading to its unusual axial tilt of 120°. The
buildup of nitrogen is due to Pluto's vast distance from the Sun. At
the equator, temperatures can drop to −240 °C
(−400.0 °F; 33.1 K), causing nitrogen to freeze as water
would freeze on Earth. The same effect seen on
Pluto would be observed
Earth if the
Antarctic ice sheet
Antarctic ice sheet was several times larger.
High-resolution MVIC image of
Pluto in enhanced color to bring out
differences in surface composition
Regions where water ice has been detected (blue regions)
Main articles: Geology of
Pluto and Geography of Pluto
The plains on Pluto's surface are composed of more than 98 percent
nitrogen ice, with traces of methane and carbon monoxide. Nitrogen
and carbon monoxide are most abundant on the anti-Charon face of Pluto
(around 180° longitude, where Tombaugh Regio's western lobe, Sputnik
Planitia, is located), whereas methane is most abundant near 300°
east. The mountains are made of water ice. Pluto's surface is
quite varied, with large differences in both brightness and color.
Pluto is one of the most contrastive bodies in the Solar System, with
as much contrast as Saturn's moon Iapetus. The color varies from
charcoal black, to dark orange and white. Pluto's color is more
similar to that of Io with slightly more orange and significantly less
red than Mars. Notable geographical features include Tombaugh
Regio, or the "Heart" (a large bright area on the side opposite
Charon), Cthulhu Macula, or the "Whale" (a large dark area on the
trailing hemisphere), and the "Brass Knuckles" (a series of equatorial
dark areas on the leading hemisphere). Sputnik Planitia, the western
lobe of the "Heart", is a 1,000 km-wide basin of frozen nitrogen
and carbon monoxide ices, divided into polygonal cells, which are
interpreted as convection cells that carry floating blocks of water
ice crust and sublimation pits towards their margins;
there are obvious signs of glacial flows both into and out of the
basin. It has no craters that were visible to New Horizons,
indicating that its surface is less than 10 million years old.
Latest studies have shown that the surface has an age of
−40000 years. The
New Horizons science team summarized initial
findings as "
Pluto displays a surprisingly wide variety of geological
landforms, including those resulting from glaciological and
surface–atmosphere interactions as well as impact, tectonic,
possible cryovolcanic, and mass-wasting processes."
Distribution of over 1000 craters of all ages on Pluto. The variation
in density (with none found in Sputnik Planitia) indicates a long
history of varying geological activity.
Geologic map of
Sputnik Planitia and surroundings (context), with
convection cell margins outlined in black
Sputnik Planitia is covered with churning nitrogen ice "cells" that
are geologically young and turning over due to convection.
Internal structure of Pluto
1. Frozen nitrogen
2. Water ice
Pluto's density is 7003186000000000000♠1.860±0.013 g/cm3.
Because the decay of radioactive elements would eventually heat the
ices enough for the rock to separate from them, scientists expect that
Pluto's internal structure is differentiated, with the rocky material
having settled into a dense core surrounded by a mantle of water ice.
The diameter of the core is hypothesized to be approximately
7006170000000000000♠1700 km, 70% of Pluto's diameter. It
is possible that such heating continues today, creating a subsurface
ocean of liquid water 100 to 180 km thick at the core–mantle
boundary. In September 2016, scientists at Brown
University simulated the impact thought to have formed Sputnik
Planitia, and showed that it might have been the result of liquid
water upwelling from below after the collision, implying the existence
of a subsurface ocean at least 100 km deep.
Pluto has no
Mass and size
Selected size estimates for Pluto
Millis, et al. (if no haze)
Millis, et al. (surface & haze)
Young & Binzel
Buie, et al.
Young, Young, & Buie
Zalucha, et al.
Lellouch, et al.
New Horizons measurement (from optical data)
New Horizons measurement (from radio occultation data)
Pluto's diameter is 7006237660000000000♠2376.6±3.2 km and
its mass is 7022130299999999999♠(1.303±0.003)×1022 kg, 17.7%
that of the
Moon (0.22% that of Earth). Its surface area is
7013177900000000000♠1.779×107 km2, or roughly the same surface
area as Russia. Its surface gravity is 0.063 g (compared to 1 g for
The discovery of Pluto's satellite Charon in 1978 enabled a
determination of the mass of the Pluto–Charon system by application
of Newton's formulation of Kepler's third law. Observations of Pluto
in occultation with Charon allowed scientists to establish Pluto's
diameter more accurately, whereas the invention of adaptive optics
allowed them to determine its shape more accurately.
Size comparisons: Earth, the Moon, and Pluto
With less than 0.2 lunar masses,
Pluto is much less massive than the
terrestrial planets, and also less massive than seven moons: Ganymede,
Titan, Callisto, Io, the Moon, Europa, and Triton. The mass is much
less than thought before Charon was discovered.
Pluto is more than twice the diameter and a dozen times the mass of
the dwarf planet Ceres, the largest object in the asteroid belt. It is
less massive than the dwarf planet Eris, a trans-Neptunian object
discovered in 2005, though
Pluto has a larger diameter of
2376.6 km compared to Eris's approximate diameter of
Determinations of Pluto's size had been complicated by its
atmosphere, and hydrocarbon haze. In March 2014, Lellouch,
de Bergh et al. published findings regarding methane mixing ratios in
Pluto's atmosphere consistent with a Plutonian diameter greater than
2360 km, with a "best guess" of 2368 km. On July 13,
2015, images from NASA's
New Horizons mission Long Range
Reconnaissance Imager (LORRI), along with data from the other
instruments, determined Pluto's diameter to be 2,370 km
(1,470 mi), which was later revised to be 2,372 km
(1,474 mi) on July 24, and later to
7006237400000000000♠2374±8 km. Using radio occultation data
New Horizons Radio Science Experiment (REX), the diameter was
found to be 7006237660000000000♠2376.6±3.2 km.
Atmosphere of Pluto
A near-true-color image taken by
New Horizons after its flyby.
Numerous layers of blue haze float in Pluto's atmosphere. Along and
near the limb, mountains and their shadows are visible.
Pluto in X-rays by
Chandra X-ray Observatory
Chandra X-ray Observatory (blue spot). The
X-rays are probably created by interaction of the gases surrounding
Pluto with solar wind, although details of their origin are not clear.
Pluto has a tenuous atmosphere consisting of nitrogen (N2), methane
(CH4), and carbon monoxide (CO), which are in equilibrium with their
ices on Pluto's surface. According to the measurements by
New Horizons, the surface pressure is about 1 Pa
(10 μbar), roughly one million to 100,000 times less than
Earth's atmospheric pressure. It was initially thought that, as Pluto
moves away from the Sun, its atmosphere should gradually freeze onto
the surface; studies of
New Horizons data and ground-based
occultations show that Pluto's atmospheric density increases, and that
it likely remains gaseous throughout Pluto's orbit. New
Horizons observations showed that atmospheric escape of nitrogen to be
10,000 times less than expected.
Alan Stern has contended that
even a small increase in Pluto's surface temperature can lead to
exponential increases in Pluto's atmospheric density; from 18 hPa
to as much as 280 hPa (three times that of
Mars to a quarter that
of the Earth). At such densities, nitrogen could flow across the
surface as liquid. Just like sweat cools the body as it
evaporates from the skin, the sublimation of Pluto's atmosphere cools
its surface. The presence of atmospheric gases was traced up to
1670 kilometers high; the atmosphere does not have a sharp upper
The presence of methane, a powerful greenhouse gas, in Pluto's
atmosphere creates a temperature inversion, with the average
temperature of its atmosphere tens of degrees warmer than its
surface, though observations by
New Horizons have revealed
Pluto's upper atmosphere to be far colder than expected (70 K, as
opposed to about 100 K). Pluto's atmosphere is divided into
roughly 20 regularly spaced haze layers up to 150 km high,
thought to be the result of pressure waves created by airflow across
Main article: Moons of Pluto
Pluto has five known natural satellites: Charon, first identified in
1978 by astronomer James Christy; Nix and Hydra, both discovered in
2005; Kerberos, discovered in 2011; and Styx, discovered in
2012. The satellites' orbits are circular (eccentricity <
0.006) and coplanar with Pluto's equator (inclination <
1°), and therefore tilted approximately 120° relative to
Pluto's orbit. The Plutonian system is highly compact: the five known
satellites orbit within the inner 3% of the region where prograde
orbits would be stable. Closest to
Pluto is Charon, which is
large enough to be in hydrostatic equilibrium and to cause the
barycenter of the Pluto–Charon system to be outside Pluto. Beyond
Charon there are four much smaller circumbinary moons, Styx, Nix,
Kerberos, and Hydra.
The orbital periods of all Pluto's moons are linked in a system of
orbital resonances and near resonances. When precession is
accounted for, the orbital periods of Styx, Nix, and Hydra are in an
exact 18:22:33 ratio. There is a sequence of approximate ratios,
3:4:5:6, between the periods of Styx, Nix, Kerberos, and Hydra with
that of Charon; the ratios become closer to being exact the further
out the moons are.
An oblique view of the Pluto–Charon system showing that
a point outside itself. The two bodies are mutually tidally locked.
The Pluto–Charon system is one of the few in the
Solar System whose
barycenter lies outside the primary body; the Patroclus–Menoetius
system is a smaller example, and the Sun–
Jupiter system is the only
larger one. The similarity in size of Charon and
prompted some astronomers to call it a double dwarf planet. The
system is also unusual among planetary systems in that each is tidally
locked to the other, which means that
Pluto and Charon always have the
same hemisphere facing each other. From any position on either body,
the other is always at the same position in the sky, or always
obscured. This also means that the rotation period of each is
equal to the time it takes the entire system to rotate around its
In 2007, observations by the
Gemini Observatory of patches of ammonia
hydrates and water crystals on the surface of Charon suggested the
presence of active cryo-geysers.
Pluto's moons are hypothesized to have been formed by a collision
Pluto and a similar-sized body, early in the history of the
Solar System. The collision released material that consolidated into
the moons around Pluto.
Pluto system: Pluto, Charon, Styx, Nix, Kerberos, and Hydra,
imaged by the
Hubble Space Telescope
Hubble Space Telescope in July 2012. 2.
Charon, to scale. Image acquired by
New Horizons on July 8, 2015. 3.
Family portrait of the five moons of Pluto, to scale. 4. Pluto's
moon Charon as viewed by
New Horizons on July 13, 2015
Kuiper belt and
Plot of the known
Kuiper belt objects, set against the four giant
Pluto's origin and identity had long puzzled astronomers. One early
hypothesis was that
Pluto was an escaped moon of Neptune, knocked
out of orbit by its largest current moon, Triton. This idea was
eventually rejected after dynamical studies showed it to be impossible
Pluto never approaches
Neptune in its orbit.
Pluto's true place in the
Solar System began to reveal itself only in
1992, when astronomers began to find small icy objects beyond Neptune
that were similar to
Pluto not only in orbit but also in size and
composition. This trans-Neptunian population is thought to be the
source of many short-period comets.
Pluto is now known to be the
largest member of the Kuiper belt,[j] a stable belt of objects located
between 30 and 50 AU from the Sun. As of 2011, surveys of the Kuiper
belt to magnitude 21 were nearly complete and any remaining
Pluto-sized objects are expected to be beyond 100 AU from the
Sun. Like other Kuiper-belt objects (KBOs),
Pluto shares features
with comets; for example, the solar wind is gradually blowing Pluto's
surface into space. It has been claimed that if
Pluto were placed
as near to the
Sun as Earth, it would develop a tail, as comets
do. This claim has been disputed with the argument that Pluto's
escape velocity is too high for this to happen.
Pluto is the largest
Kuiper belt object discovered,
Neptune's moon Triton, which is slightly larger than Pluto, is similar
to it both geologically and atmospherically, and is thought to be a
Kuiper belt object. Eris (see above) is about the same
Pluto (though more massive) but is not strictly considered a
member of the
Kuiper belt population. Rather, it is considered a
member of a linked population called the scattered disc.
A large number of
Kuiper belt objects, like Pluto, are in a 2:3
orbital resonance with Neptune. KBOs with this orbital resonance are
called "plutinos", after Pluto.
Like other members of the Kuiper belt,
Pluto is thought to be a
residual planetesimal; a component of the original protoplanetary disc
Sun that failed to fully coalesce into a full-fledged
planet. Most astronomers agree that
Pluto owes its current position to
a sudden migration undergone by
Neptune early in the Solar System's
Neptune migrated outward, it approached the objects in
the proto-Kuiper belt, setting one in orbit around itself (Triton),
locking others into resonances, and knocking others into chaotic
orbits. The objects in the scattered disc, a dynamically unstable
region overlapping the Kuiper belt, are thought to have been placed in
their current positions by interactions with Neptune's migrating
resonances. A computer model created in 2004 by Alessandro
Morbidelli of the Observatoire de la Côte d'Azur in
that the migration of
Neptune into the
Kuiper belt may have been
triggered by the formation of a 1:2 resonance between
Saturn, which created a gravitational push that propelled both Uranus
Neptune into higher orbits and caused them to switch places,
ultimately doubling Neptune's distance from the Sun. The resultant
expulsion of objects from the proto-
Kuiper belt could also explain the
Late Heavy Bombardment
Late Heavy Bombardment 600 million years after the Solar System's
formation and the origin of the
Jupiter trojans. It is possible
Pluto had a near-circular orbit about 33 AU from the
Neptune's migration perturbed it into a resonant capture. The
Nice model requires that there were about a thousand Pluto-sized
bodies in the original planetesimal disk, which included Triton and
Observation and exploration
Pluto's distance from
Earth makes its in-depth study and exploration
difficult. On July 14, 2015, NASA's
New Horizons space probe flew
Pluto system, providing much information about it.
Computer-generated rotating image of
Pluto based on observations by
Hubble Space Telescope
Hubble Space Telescope in 2002–2003
Pluto's visual apparent magnitude averages 15.1, brightening to 13.65
at perihelion. To see it, a telescope is required; around
30 cm (12 in) aperture being desirable. It looks
star-like and without a visible disk even in large telescopes, because
its angular diameter is only 0.11".
The earliest maps of Pluto, made in the late 1980s, were brightness
maps created from close observations of eclipses by its largest moon,
Charon. Observations were made of the change in the total average
brightness of the Pluto–Charon system during the eclipses. For
example, eclipsing a bright spot on
Pluto makes a bigger total
brightness change than eclipsing a dark spot. Computer processing of
many such observations can be used to create a brightness map. This
method can also track changes in brightness over time.
Better maps were produced from images taken by the Hubble Space
Telescope (HST), which offered higher resolution, and showed
considerably more detail, resolving variations several hundred
kilometers across, including polar regions and large bright spots.
These maps were produced by complex computer processing, which finds
the best-fit projected maps for the few pixels of the Hubble
images. These remained the most detailed maps of
Pluto until the
New Horizons in July 2015, because the two cameras on the HST
used for these maps were no longer in service.
Main articles: Exploration of
Pluto and New Horizons
The portions of Pluto's surface mapped by
New Horizons (annotated)
New Horizons spacecraft, which flew by
Pluto in July 2015, is the
first and so far only attempt to explore
Pluto directly. Launched in
2006, it captured its first (distant) images of
Pluto in late
September 2006 during a test of the Long Range Reconnaissance
Imager. The images, taken from a distance of approximately 4.2
billion kilometers, confirmed the spacecraft's ability to track
distant targets, critical for maneuvering toward
Pluto and other
Kuiper belt objects. In early 2007 the craft made use of a gravity
assist from Jupiter.
New Horizons made its closest approach to
Pluto on July 14, 2015,
after a 3,462-day journey across the Solar System. Scientific
Pluto began five months before the closest approach
and continued for at least a month after the encounter. Observations
were conducted using a remote sensing package that included imaging
instruments and a radio science investigation tool, as well as
spectroscopic and other experiments. The scientific goals of New
Horizons were to characterize the global geology and morphology of
Pluto and its moon Charon, map their surface composition, and analyze
Pluto's neutral atmosphere and its escape rate. On October 25, 2016,
at 05:48 pm ET, the last bit of data (of a total of 50 billion bits of
data; or 6.25 gigabytes) was received from
New Horizons from its close
encounter with Pluto.
Pluto flyover animated (July 14, 2015)
(00:30; released September 18, 2015)
(00:50; released December 5, 2015)
This mosaic strip – extending across the hemisphere that faced the
New Horizons spacecraft as it flew past Pluto. (No Audio – 1080p
Solar System portal
Book: Dwarf Planets of the
Solar System & Their Satellites
Book: Solar System
How I Killed
Pluto and Why It Had It Coming
Pluto in astrology
Pluto in fiction
^ This is a composite of four near-true color photographs taken by the
New Horizons spacecraft on July 14, 2015 from a distance of
720,000 km (450,000 mi). The most prominent feature in the
image, the bright, youthful plains of
Tombaugh Regio and Sputnik
Planitia, can be seen at lower right. It contrasts the darker, more
cratered terrain of Cthulhu Macula at lower left. Because of
Pluto's 119.591° tilt at its axis, the southern hemisphere is barely
visible in this image; the equator runs through Cthulhu and the
southern parts of Sputnik Planitia.
^ The mean elements here are from the Theory of the Outer Planets
(TOP2013) solution by the Institut de mécanique céleste et de calcul
des éphémérides (IMCCE). They refer to the standard equinox J2000,
the barycenter of the Solar System, and the epoch J2000.
Surface area derived from the radius r:
displaystyle 4pi r^ 2
Volume v derived from the radius r:
displaystyle 4pi r^ 3 /3
Surface gravity derived from the mass M, the gravitational constant
G and the radius r:
displaystyle GM/r^ 2
Escape velocity derived from the mass M, the gravitational constant
G and the radius r:
displaystyle sqrt 2GM/r
^ Based on geometry of minimum and maximum distance from
Pluto radius in the factsheet
^ The equivalence is less close in languages whose phonology differs
widely from Greek's, such as Somali Buluuto and Navajo Tłóotoo.
^ The discovery of Charon in 1978 allowed astronomers to accurately
calculate the mass of the Plutonian system. But it did not indicate
the two bodies' individual masses, which could only be estimated after
other moons of
Pluto were discovered in late 2005. As a result,
Pluto came to perihelion in 1989, most
Pluto perihelion date
estimates are based on the Pluto–Charon barycenter. Charon came to
perihelion 4 September 1989. The Pluto–Charon barycenter came to
perihelion 5 September 1989.
Pluto came to perihelion 8 September
^ The dwarf planet Eris is roughly the same size as Pluto, about
2330 km; Eris is 28% more massive than Pluto. Eris is a
scattered-disc object, often considered a distinct population from
Kuiper-belt objects like Pluto;
Pluto is the largest body in the
Kuiper belt proper, which excludes the scattered-disc objects.
^ a b c d e Stern, S. A.; Grundy, W.; McKinnon, W. B.; Weaver, H. A.;
Young, L. A. "The
Pluto System After New Horizons".
^ a b c d e f g h i j k l Williams, David R. (July 24, 2015). "Pluto
Fact Sheet". NASA. Retrieved August 6, 2015.
^ a b "Horizon Online Ephemeris System for
Pluto Barycenter". JPL
Horizons On-Line Ephemeris System @
Solar System Dynamics Group.
Retrieved January 16, 2011. (set Observer Location to @0 to
place the observer at the center of the Sun-
^ Simon, J.L.; Francou, G.; Fienga, A.; Manche, H. (September 2013).
"New analytical planetary theories VSOP2013 and TOP2013". Astronomy
and Astrophysics. 557 (2): A49. Bibcode:2013A&A...557A..49S.
doi:10.1051/0004-6361/201321843. The elements in the clearer and
usual format is in the spreadsheet and the original TOP2013 elements
^ a b c d e Nimmo, Francis; et al. (2017). "Mean radius and shape of
Pluto and Charon from
New Horizons images". Icarus. 287: 12–29.
arXiv:1603.00821 . Bibcode:2017Icar..287...12N.
^ a b c d e f g h i Stern, S. A.; et al. (2015). "The
Initial results from its exploration by New Horizons". Science. 350
(6258): 249–352. arXiv:1510.07704 . Bibcode:2015Sci...350.1815S.
doi:10.1126/science.aad1815. PMID 26472913.
^ a b Archinal, B. A.; a'Hearn, M. F.; Bowell, E.; Conrad, A.;
Consolmagno, G. J.; et al. (2010). "Report of the IAU Working Group on
Cartographic Coordinates and Rotational Elements: 2009". Celestial
Mechanics and Dynamical Astronomy. 109 (2): 101–135.
^ Hamilton, Calvin J. (February 12, 2006). "Dwarf
Planet Pluto". Views
of the Solar System. Retrieved January 10, 2007.
^ "AstDys (134340)
Pluto Ephemerides". Department of Mathematics,
University of Pisa, Italy. Retrieved June 27, 2010.
^ "JPL Small-Body Database Browser: 134340 Pluto". Retrieved June 12,
Pluto has carbon monoxide in its atmosphere". Physorg.com. April
19, 2011. Retrieved November 22, 2011.
^ Amos, Jonathan (July 23, 2015). "New Horizons:
Pluto may have
'nitrogen glaciers'". BBC News. Retrieved July 26, 2015. It could tell
from the passage of sunlight and radiowaves through the Plutonian
"air" that the pressure was only about 10 microbars at the
^ Croswell, Ken (1997).
Planet Quest: The Epic Discovery of Alien
Solar Systems. New York: The Free Press. p. 43.
^ a b c Tombaugh, Clyde W. (1946). "The Search for the Ninth Planet,
Pluto". Astronomical Society of the Pacific Leaflets. 5: 73–80.
^ a b c Hoyt, William G. (1976). "W. H. Pickering's Planetary
Predictions and the Discovery of Pluto". Isis. 67 (4): 551–564.
doi:10.1086/351668. JSTOR 230561.
^ Littman, Mark (1990). Planets Beyond: Discovering the Outer Solar
System. Wiley. p. 70. ISBN 0-471-51053-X.
^ Buchwald, Greg; Dimario, Michael; Wild, Walter (2000). "
Discovered Back in Time". Amateur—Professional Partnerships in
Astronomy. San Francisco: San Francisco: Astronomical Society of the
Pacific. 220: 335. Bibcode:2000ASPC..220..355B.
^ a b Croswell 1997, p. 50.
^ Croswell 1997, p. 52.
^ For example: "Ninth
Planet Discovered on Edge of Solar System: First
Found in 84 Years". Associated Press. The New York Times. March 14,
1930. p. 1.
^ a b Rao, Joe (March 11, 2005). "Finding Pluto: Tough Task, Even 75
Years Later". Space.com. Retrieved September 8, 2006.
^ Mager, Brad. "The Search Continues". Pluto: The Discovery of Planet
X. Retrieved November 29, 2011.
^ a b c d Rincon, Paul (January 13, 2006). "The girl who named a
planet". BBC News. Retrieved April 12, 2007.
^ Croswell 1997, pp. 54–55.
Pluto Research at Lowell". Lowell Observatory. Retrieved March 22,
2017. In a
Lowell Observatory Circular dated May 1, 1930, the
Pluto as the name for the new planet, based on
the suggestion of 11-year-old
Venetia Burney of England.
Retail Price Index
Retail Price Index inflation figures are based on data from
Clark, Gregory (2017). "The Annual RPI and Average Earnings for
Britain, 1209 to Present (New Series)". MeasuringWorth. Retrieved
November 6, 2017.
Solar System Exploration: Multimedia: Gallery: Pluto's
Symbol". NASA. Archived from the original on October 1, 2006.
Retrieved November 29, 2011.
^ Heinrichs, Allison M. (2006). "Dwarfed by comparison". Pittsburgh
Tribune-Review. Archived from the original on November 14, 2007.
Retrieved March 26, 2007.
^ Clark, David L.; Hobart, David E. (2000). "Reflections on the Legacy
of a Legend" (PDF). Retrieved November 29, 2011.
^ Renshaw, Steve; Ihara, Saori (2000). "A Tribute to Houei Nojiri".
Archived from the original on December 6, 2012. Retrieved November 29,
^ a b c "Planetary Linguistics". Archived from the original on
December 17, 2007. Retrieved June 12, 2007.
^ 'Bathrobe'. "Uranus, Neptune, and
Pluto in Chinese, Japanese, and
Vietnamese". cjvlang.com. Archived from the original on August 20,
2011. Retrieved November 29, 2011.
^ Stern, Alan; Tholen, David James (1997).
Pluto and Charon.
University of Arizona
University of Arizona Press. pp. 206–208.
^ Crommelin, Andrew Claude de la Cherois (1931). "The Discovery of
Pluto". Monthly Notices of the Royal Astronomical Society. 91 (4):
^ a b Nicholson, Seth B.; Mayall, Nicholas U. (December 1930). "The
Probable Value of the
Mass of Pluto". Publications of the Astronomical
Society of the Pacific. 42 (250): 350. Bibcode:1930PASP...42..350N.
^ Nicholson, Seth B.; Mayall, Nicholas U. (January 1931). "Positions,
Mass of Pluto". Astrophysical Journal. 73: 1.
^ a b Kuiper, Gerard P. (1950). "The Diameter of Pluto". Publications
of the Astronomical Society of the Pacific. 62 (366): 133–137.
^ a b Croswell 1997, p. 57.
^ Christy, James W.; Harrington, Robert Sutton (1978). "The Satellite
of Pluto". Astronomical Journal. 83 (8): 1005–1008.
^ a b Buie, Marc W.; Grundy, William M.; Young, Eliot F.; et al.
(2006). "Orbits and photometry of Pluto's satellites: Charon, S/2005
P1, and S/2005 P2". Astronomical Journal. 132 (1): 290–298.
arXiv:astro-ph/0512491 . Bibcode:2006AJ....132..290B.
^ Seidelmann, P. Kenneth; Harrington, Robert Sutton (1988). "Planet
X – The current status". Celestial Mechanics and Dynamical
Astronomy. 43: 55–68. Bibcode:1987CeMec..43...55S.
doi:10.1007/BF01234554. Retrieved November 29, 2011.
^ a b Standish, E. Myles (1993). "
Planet X—No dynamical evidence in
the optical observations". Astronomical Journal. 105 (5): 200–2006.
^ Standage, Tom (2000). The
Neptune File. Penguin. p. 168.
^ "History I: The
Lowell Observatory in 20th century Astronomy". The
Astronomical Society of the Pacific. June 28, 1994. Retrieved November
^ Tyson, Neil deGrasse (February 2, 2001). "Astronomer Responds to
Planet Claim". Space.com. Retrieved November 30,
^ "NASA-Funded Scientists Discover Tenth Planet".
NASA press releases.
July 29, 2005. Retrieved February 22, 2007.
^ a b Soter, Steven (2007). "What is a Planet?". The Astronomical
Journal. Department of Astrophysics, American Museum of Natural
History. 132 (6): 2513–2519. arXiv:astro-ph/0608359 .
^ "IAU 2006 General Assembly: Resolutions 5 and 6" (PDF). IAU. August
^ a b "IAU 2006 General Assembly: Result of the IAU Resolution votes".
International Astronomical Union
International Astronomical Union (News Release – IAU0603). August
24, 2006. Retrieved June 15, 2008.
^ Green, Daniel W. E. (September 13, 2006). "(134340) Pluto, (136199)
Eris, and (136199) Eris I (Dysnomia)" (PDF). IAU Circular. 8747.
Archived from the original on February 5, 2007. Retrieved December 1,
^ "JPL Small-Body Database Browser". California Institute of
Technology. Retrieved July 15, 2015.
^ Britt, Robert Roy (August 24, 2006). "
Pluto Demoted: No Longer a
Planet in Highly Controversial Definition". Space.com. Archived from
the original on August 20, 2011. Retrieved September 8, 2006.
^ Ruibal, Sal (January 6, 1999). "Astronomers question if
real planet". USA Today.
^ Britt, Robert Roy (November 21, 2006). "Why Planets Will Never Be
Defined". Space.com. Retrieved December 1, 2006.
^ Britt, Robert Roy (August 24, 2006). "Scientists decide Pluto's no
longer a planet". MSNBC. Retrieved September 8, 2006.
^ a b Shiga, David (August 25, 2006). "New planet definition sparks
furore". NewScientist.com. Retrieved September 8, 2006.
^ "Should Large Moons Be Called 'Satellite Planets'?".
News.discovery.com. May 14, 2010. Retrieved November 4, 2011.
^ Buie, Marc W. (September 2006). "My response to 2006 IAU Resolutions
5a and 6a". Southwest Research Institute. Archived from the original
on June 3, 2007. Retrieved December 1, 2011.
^ Overbye, Dennis (August 24, 2006). "
Pluto Is Demoted to 'Dwarf
Planet'". The New York Times. Retrieved December 1, 2011.
^ DeVore, Edna (September 7, 2006). "Planetary Politics: Protecting
Pluto". Space.com. Retrieved December 1, 2011.
^ Holden, Constance (March 23, 2007). "Rehabilitating Pluto". Science.
315 (5819): 1643. doi:10.1126/science.315.5819.1643c.
^ Gutierrez, Joni Marie (2007). "A joint memorial. Declaring
planet and declaring March 13, 2007, '
Pluto planet day' at the
legislature". Legislature of New Mexico. Retrieved September 5,
^ "Illinois General Assembly: Bill Status of SR0046, 96th General
Assembly". ilga.gov. Illinois General Assembly. Retrieved March 16,
^ "Pluto's still the same Pluto". Independent Newspapers. Associated
Press. October 21, 2006. Retrieved November 29, 2011.
Mickey Mouse has
a cute dog.
^ "'Plutoed' chosen as '06 Word of the Year". Associated Press.
January 8, 2007. Retrieved January 10, 2007.
^ Minkel, J. R. (April 10, 2008). "Is Rekindling the
Debate a Good Idea?". Scientific American. Retrieved December 1,
^ "The Great
Planet Debate: Science as Process. A Scientific
Conference and Educator Workshop". gpd.jhuapl.edu. Johns Hopkins
University Applied Physics Laboratory. June 27, 2008. Retrieved
December 1, 2011.
^ "Scientists Debate
Planet Definition and Agree to Disagree",
Planetary Science Institute press release of September 19, 2008,
Plutoid chosen as name for
Solar System objects like Pluto". Paris:
International Astronomical Union
International Astronomical Union (News Release – IAU0804). June 11,
2008. Retrieved December 1, 2011.
^ "Plutoids Join the Solar Family", Discover Magazine, January 2009,
^ Science News, July 5, 2008, p. 7
Pluto to become most distant planet". JPL/NASA. January 28, 1999.
Retrieved January 16, 2011.
^ Sussman, Gerald Jay; Wisdom, Jack (1988). "Numerical evidence that
the motion of
Pluto is chaotic". Science. 241 (4864): 433–437.
^ Wisdom, Jack; Holman, Matthew (1991). "Symplectic maps for the
n-body problem". Astronomical Journal. 102: 1528–1538.
^ a b c d Williams, James G.; Benson, G. S. (1971). "Resonances in the
Pluto System". Astronomical Journal. 76: 167.
^ a b c d Wan, Xiao-Sheng; Huang, Tian-Yi; Innanen, Kim A. (2001).
"The 1:1 Superresonance in Pluto's Motion". The Astronomical Journal.
121 (2): 1155–1162. Bibcode:2001AJ....121.1155W.
^ Hunter, Maxwell W. (2004). "Unmanned scientific exploration
throughout the Solar System". Space Science Reviews. 6 (5): 501.
^ a b c d Malhotra, Renu (1997). "Pluto's Orbit". Retrieved March 26,
^ a b c Alfvén, Hannes; Arrhenius, Gustaf (1976). "SP-345 Evolution
of the Solar System". Retrieved March 28, 2007.
^ Cohen, C. J.; Hubbard, E. C. (1965). "
Libration of the close
Pluto to Neptune". Astronomical Journal. 70: 10.
^ a b de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2012).
Plutino 15810 (1994 JR1), an accidental quasi-satellite of Pluto".
Monthly Notices of the Royal Astronomical Society Letters. 427: L85.
arXiv:1209.3116 . Bibcode:2012MNRAS.427L..85D.
^ "Pluto's fake moon". Retrieved September 24, 2012.
New Horizons Collects First Science on a Post-
^ a b Faure, Gunter; Mensing, Teresa M. (2007).
Pluto and Charon: The
Odd Couple. Introduction to Planetary Science. Springer.
pp. 401–408. doi:10.1007/978-1-4020-5544-7.
^ Schombert, Jim; University of Oregon
Astronomy 121 Lecture notes,
Pluto Orientation diagram
^ Kirschvink, Joseph L.; Ripperdan, Robert L.; Evans, David A. (July
25, 1997). "Evidence for a Large-Scale Reorganization of Early
Cambrian Continental Masses by Inertial Interchange True Polar
Wander". Science. 277 (5325): 541–545.
doi:10.1126/science.277.5325.541. ISSN 0036-8075.
^ Keane, James T.; Matsuyama, Isamu; Kamata, Shunichi; Steckloff,
Jordan K. (2016). "Reorientation and faulting of
Pluto due to volatile
loading within Sputnik Planitia". Nature. 540 (7631): 90–93.
^ a b Owen, Tobias C.; Roush, Ted L.; Cruikshank, Dale P.; et al.
(1993). "Surface Ices and the Atmospheric Composition of Pluto".
Science. 261 (5122): 745–748. Bibcode:1993Sci...261..745O.
doi:10.1126/science.261.5122.745. JSTOR 2882241.
^ Grundy, W. M.; Olkin, C. B.; Young, L. A.; Buie, M. W.; Young, E. F.
(2013). "Near-infrared spectral monitoring of Pluto's ices: Spatial
distribution and secular evolution" (PDF). Icarus. 223 (2): 710–721.
arXiv:1301.6284 . Bibcode:2013Icar..223..710G.
doi:10.1016/j.icarus.2013.01.019. Archived from the original (PDF) on
November 8, 2015.
^ Drake, Nadia (November 9, 2015). "Floating Mountains on Pluto—You
Can't Make This Stuff Up". National Geographic. Retrieved December 23,
^ Buie, Marc W.; Grundy, William M.; Young, Eliot F.; et al. (2010).
Pluto and Charon with the Hubble Space Telescope: I. Monitoring
global change and improved surface properties from light curves".
Astronomical Journal. 139 (3): 1117–1127.
^ a b Buie, Marc W. "
Pluto map information". Archived from the
original on June 29, 2011. Retrieved February 10, 2010.
^ Villard, Ray; Buie, Marc W. (February 4, 2010). "New Hubble Maps of
Pluto Show Surface Changes". News Release Number: STScI-2010-06.
Retrieved February 10, 2010.
^ a b Buie, Marc W.; Grundy, William M.; Young, Eliot F.; et al.
Pluto and Charon with the Hubble Space Telescope: II.
Resolving changes on Pluto's surface and a map for Charon".
Astronomical Journal. 139 (3): 1128–1143.
^ Lakdawalla, Emily (October 26, 2016). "DPS/EPSC update on New
Horizons at the
Pluto system and beyond". The Planetary Society.
Retrieved October 26, 2016.
^ McKinnon, W. B.; Nimmo, F.; Wong, T.; Schenk, P. M.; White, O. L.;
et al. (June 1, 2016). "Convection in a volatile nitrogen-ice-rich
layer drives Pluto's geological vigour". Nature. 534 (7605): 82–85.
^ Trowbridge, A. J.; Melosh, H. J.; Steckloff, J. K.; Freed, A. M.
(June 1, 2016). "Vigorous convection as the explanation for Pluto's
polygonal terrain". Nature. 534 (7605): 79–81.
^ Lakdawalla, Emily (December 21, 2015). "
Pluto updates from AGU and
DPS: Pretty pictures from a confusing world". The Planetary Society.
Retrieved January 24, 2016.
^ Umurhan, O. (January 8, 2016). "Probing the Mysterious Glacial Flow
on Pluto's Frozen 'Heart'". blogs.nasa.gov. NASA. Retrieved January
^ Marchis, F.; Trilling, D. E. (January 20, 2016). "The Surface Age of
Sputnik Planum, Pluto, Must Be Less than 10 Million Years". PLoS ONE.
11 (1): e0147386. arXiv:1601.02833 . Bibcode:2016PLoSO..1147386T.
doi:10.1371/journal.pone.0147386. PMC 4720356 .
^ Buhler, P. B.; Ingersoll, A. P. (March 23, 2017). "Sublimation pit
distribution indicates convection cell surface velocity of ~10
centimeters per year in Sputnik Planitia, Pluto" (PDF). 48th Lunar and
Planetary Science Conference.
^ a b c Hussmann, Hauke; Sohl, Frank; Spohn, Tilman (November 2006).
"Subsurface oceans and deep interiors of medium-sized outer planet
satellites and large trans-neptunian objects" (PDF). Icarus. 185 (1):
^ "The Inside Story". pluto.jhuapl.edu –
NASA New Horizons
mission site. Johns Hopkins University Applied Physics Laboratory.
2007. Retrieved February 15, 2014.
^ Overlooked Ocean Worlds Fill the Outer Solar System. John Wenz,
Scientific American. October 4, 2017.
^ Samantha Cole. "An Incredibly Deep Ocean Could Be Hiding Beneath
Pluto's Icy Heart". Popular Science. Retrieved September 24,
NASA (September 14, 2016). "X-ray Detection Sheds New Light on
Pluto". nasa.gov. Retrieved December 3, 2016.
^ Millis, Robert L.; Wasserman, Lawrence H.; Franz, Otto G.; et al.
(1993). "Pluto's radius and atmosphere – Results from the
entire 9 June 1988 occultation data set". Icarus. 105 (2): 282–297.
^ a b c d Brown, Michael E. (November 22, 2010). "How big is Pluto,
anyway?". Mike Brown's Planets. Retrieved June 9, 2015. (Franck
Marchis on 8 November 2010)
^ Young, Eliot F.; Binzel, Richard P. (1994). "A new determination of
radii and limb parameters for
Pluto and Charon from mutual event
lightcurves". Icarus. 108 (2): 219–224. Bibcode:1994Icar..108..219Y.
^ a b Young, Eliot F.; Young, Leslie A.; Buie, Marc W. (2007).
"Pluto's Radius". American Astronomical Society, DPS meeting No. 39,
#62.05; Bulletin of the American Astronomical Society. 39: 541.
^ Zalucha, Angela M.; Gulbis, Amanda A. S.; Zhu, Xun; et al. (2011).
"An analysis of
Pluto occultation light curves using an atmospheric
radiative-conductive model". Icarus. 211 (1): 804–818.
^ a b Lellouch, Emmanuel; de Bergh, Catherine; Sicardy, Bruno; et al.
(January 15, 2015). "Exploring the spatial, temporal, and vertical
distribution of methane in Pluto's atmosphere". Icarus. 246:
268–278. arXiv:1403.3208 . Bibcode:2015Icar..246..268L.
^ a b NASA's
New Horizons Team Reveals New Scientific Findings on
Pluto. NASA. July 24, 2015. Event occurs at 52:30. Retrieved July 30,
2015. We had an uncertainty that ranged over maybe 70 kilometers,
we've collapsed that to plus and minus two, and it's centered around
^ Davies, John (2001). "Beyond
Pluto (extract)" (PDF). Royal
Observatory, Edinburgh. Retrieved March 26, 2007.
^ Close, Laird M.; Merline, William J.; Tholen, David J.; et al.
Adaptive optics imaging of Pluto–Charon and the discovery
of a moon around the
Asteroid 45 Eugenia: the potential of adaptive
optics in planetary astronomy". Proceedings of the International
Society for Optical Engineering. Adaptive Optical Systems Technology.
European Southern Observatory. 4007: 787–795.
^ a b "How Big Is Pluto?
New Horizons Settles Decades-Long Debate".
NASA. July 13, 2015. Retrieved July 13, 2015.
^ Lakdawalla, Emily (July 13, 2015). "
Pluto minus one day: Very first
Pluto encounter science results". The Planetary Society.
Retrieved July 13, 2015.
^ "Conditions on Pluto: Incredibly Hazy With Flowing Ice". New York
Times. July 24, 2015. Retrieved July 24, 2015.
^ Croswell, Ken (1992). "
Nitrogen in Pluto's Atmosphere".
KenCroswell.com. New Scientist. Retrieved April 27, 2007.
^ Olkin, C. B.; Young, L. A.; Borncamp, D.; et al. (January 2015).
"Evidence that Pluto's atmosphere does not collapse from occultations
including the 2013 May 04 event". Icarus. 246: 220–225.
^ a b c d e Kelly Beatty (2016). "Pluto's
Researchers". Sky & Telescope. Retrieved April 2, 2016.
^ Than, Ker (2006). "Astronomers:
Pluto colder than expected".
Space.com (via CNN.com). Retrieved November 30, 2011.
^ Lellouch, Emmanuel; Sicardy, Bruno; de Bergh, Catherine; et al.
(2009). "Pluto's lower atmosphere structure and methane abundance from
high-resolution spectroscopy and stellar occultations".
Astrophysics. 495 (3): L17–L21. arXiv:0901.4882 .
^ Gugliotta, Guy (November 1, 2005). "Possible New Moons for Pluto".
Washington Post. Retrieved October 10, 2006.
^ "NASA's Hubble Discovers Another
Moon Around Pluto". NASA. July 20,
2011. Retrieved July 20, 2011.
^ Wall, Mike (July 11, 2012). "
Pluto Has a Fifth Moon, Hubble
Telescope Reveals". Space.com. Retrieved July 11, 2012.
^ Buie, M.; Tholen, D.; Grundy, W. (2012). "The Orbit of Charon is
Circular". The Astronomical Journal. 144: 15.
^ a b c d Showalter, M. R.; Hamilton, D. P. (June 3, 2015). "Resonant
interactions and chaotic rotation of Pluto's small moons". Nature. 522
(7554): 45–49. Bibcode:2015Natur.522...45S. doi:10.1038/nature14469.
^ Stern, S. Alan; Weaver, Harold A., Jr.; Steffl, Andrew J.; et al.
(2005). "Characteristics and Origin of the Quadruple System at Pluto".
Submitted to Nature: arXiv:astro–ph/0512599.
arXiv:astro-ph/0512599 . Bibcode:2005astro.ph.12599S.
^ Witze, Alexandra (2015). "Pluto's moons move in synchrony". Nature.
^ Matson, J. (July 11, 2012). "New
Moon for Pluto: Hubble Telescope
Spots a 5th Plutonian Satellite".
Scientific American web site.
Retrieved July 12, 2012.
^ Richardson, Derek C.; Walsh, Kevin J. (2005). "Binary Minor
Planets". Annual Review of
Earth and Planetary Sciences. 34 (1):
^ Sicardy, Bruno; Bellucci, Aurélie; Gendron, Éric; et al. (2006).
"Charon's size and an upper limit on its atmosphere from a stellar
occultation". Nature. 439 (7072): 52–4. Bibcode:2006Natur.439...52S.
doi:10.1038/nature04351. PMID 16397493.
^ Young, Leslie A. (1997). "The Once and Future Pluto". Southwest
Research Institute, Boulder, Colorado. Retrieved March 26, 2007.
^ "Charon: An ice machine in the ultimate deep freeze". Gemini
Observatory News Release. 2007. Retrieved July 18, 2007.
^ "NASA's Hubble Finds Pluto's Moons Tumbling in Absolute Chaos".
Retrieved June 3, 2015.
^ "HubbleSite – NewsCenter – Hubble Finds Two Chaotically Tumbling
Pluto Moons (06/03/2015) – Introduction". hubblesite.org. Retrieved
June 3, 2015.
^ Ley, Willy (August 1956). "The Demotion of Pluto". For Your
Information. Galaxy Science Fiction. pp. 79–91.
^ Stern, S. Alan; Tholen, David J. (1997).
Pluto and Charon.
University of Arizona
University of Arizona Press. p. 623.
^ Sheppard, Scott S.; Trujillo, Chadwick A.; Udalski, Andrzej; et al.
(2011). "A Southern Sky and Galactic Plane Survey for Bright Kuiper
Belt Objects". Astronomical Journal. 142 (4): 98. arXiv:1107.5309 .
^ "Colossal Cousin to a Comet?". pluto.jhuapl.edu –
Horizons mission site. Johns Hopkins University Applied Physics
Laboratory. Archived from the original on November 13, 2014. Retrieved
February 15, 2014.
^ Tyson, Neil deGrasse (1999). "
Pluto Is Not a Planet". The Planetary
Society. Archived from the original on September 27, 2011. Retrieved
November 30, 2011.
^ "Nine Reasons Why
Pluto Is a Planet" by Philip Metzger
Moon Triton". The Planetary Society. Archived from the
original on December 10, 2011. Retrieved November 30, 2011.
^ Jewitt, David C. (2004). "The Plutinos". University of Hawaii.
Archived from the original on April 19, 2007. Retrieved March 26,
^ Hahn, Joseph M. (2005). "Neptune's Migration into a Stirred–Up
Kuiper Belt: A Detailed Comparison of Simulations to Observations"
(PDF). Saint Mary's University. Retrieved March 5, 2008.
^ a b Levison, Harold F.; Morbidelli, Alessandro; Van Laerhoven,
Christa; et al. (2007). "Origin of the Structure of the Kuiper Belt
during a Dynamical Instability in the Orbits of
Uranus and Neptune".
Icarus. 196 (1): 258–273. arXiv:0712.0553 .
^ Malhotra, Renu (1995). "The Origin of Pluto's Orbit: Implications
Solar System Beyond Neptune". Astronomical Journal. 110: 420.
arXiv:astro-ph/9504036 . Bibcode:1995AJ....110..420M.
^ Talbert, Tricia (March 17, 2016). "Top
New Horizons Findings
Reported in Science". NASA. Retrieved March 18, 2016.
^ "This month Pluto's apparent magnitude is m=14.1. Could we see it
with an 11" reflector of focal length 3400 mm?". Singapore
Science Centre. 2002. Archived from the original on November 11, 2005.
Retrieved November 29, 2011.
^ Young, Eliot F.; Binzel, Richard P.; Crane, Keenan (2001). "A
Two-Color Map of Pluto's Sub-Charon Hemisphere". The Astronomical
Journal. 121 (1): 552–561. Bibcode:2001AJ....121..552Y.
^ Buie, Marc W.; Tholen, David J.; Horne, Keith (1992). "
Pluto and Charon: Initial mutual event results". Icarus. 97 (2):
^ a b Buie, Marc W. "How the
Pluto maps were made". Archived from the
original on February 9, 2010. Retrieved February 10, 2010.
^ "New Horizons, Not Quite to Jupiter, Makes First
New Horizons mission site. Johns
Hopkins University Applied Physics Laboratory. November 28, 2006.
Archived from the original on March 9, 2011. Retrieved November 29,
^ Chang, Kenneth (October 28, 2016). "No More Data From Pluto". New
York Times. Retrieved October 28, 2016.
Pluto Exploration Complete:
New Horizons Returns Last Bits of 2015
Flyby Data to Earth". Johns Hopkins Applied Research Laboratory.
October 27, 2016. Retrieved October 28, 2016.
^ Brown, Dwayne; Buckley, Michael; Stothoff, Maria (January 15, 2015).
"January 15, 2015 Release 15-011 – NASA's
New Horizons Spacecraft
Begins First Stages of
Pluto Encounter". NASA. Retrieved January 15,
^ "New Horizons". pluto.jhuapl.edu. Retrieved May 15, 2016.
Stern, S A and Tholen, D J (1997),
Pluto and Charon, University of
Arizona Press ISBN 978-0816518401
Find more aboutPlutoat's sister projects
Definitions from Wiktionary
Media from Wikimedia Commons
News from Wikinews
Quotations from Wikiquote
Texts from Wikisource
Textbooks from Wikibooks
Learning resources from Wikiversity
New Horizons homepage
Pluto Profile at NASA's
Solar System Exploration site
Website of the observatory that discovered Pluto
Earth telescope image of
Keck infrared with AO of
Gray, Meghan (2009). "Pluto". Sixty Symbols.
Brady Haran for the
University of Nottingham.
Pluto – viewed through the years (GIF) (NASA; animation;
July 15, 2015).
Pluto – "FlyThrough" (00:22; MP4) (YouTube) (NASA;
animation; August 31, 2015).
"A Day on
Pluto Video made from July 2015 New Horizon Images"
NASA CGI video of
Pluto flyover (July 14, 2017)
CGI video simulation of rotating
Pluto by Seán Doran (see album for
Pluto 3D, interactive map of the dwarf planet
Articles related to Pluto
Coleta de Dados Colles
Definition of planet
IAU definition of planet
International Astronomical Union
Michael E. Brown
Neil deGrasse Tyson
James W. Christy
Solar eclipses on Pluto
Hubble Space Telescope
Pluto Fast Flyby/
Pluto Kuiper Express
Mariner Mark II
No longer rounded and therefore not dwarf planets (Former candidates:
1995 SN55 (lost)
Additional objects proposed by Brown and Tancredi: Orcus
Possibly: 2003 UZ413
Possibly: 2002 WC19
Possibly: 2002 XW93
Additional objects proposed by Brown and Tancredi: 2002 MS4
Additional objects proposed by Brown and Tancredi: 2007 OR10
Possibly: 2002 TC302
Captured satellites that were once dwarf planets: Triton (captured by
Phoebe (captured by Saturn, and no longer rounded)
2011 FW62 (lost)
Possibly: 2004 XR190
Objects proposed by Brown and Tancredi: Sedna
Possibly: 2012 VP113
See also: Charon
List of trans-Neptunian objects
List of possible dwarf planets
Solar System objects
Solar System objects by size
Dwarf planets (moons)
S/2015 (136472) 1
Minor planets navigator
(134339) 5628 T-3
(134341) 1979 MA
The Solar System
S/2015 (136472) 1
Solar System objects
By discovery date
Gravitationally rounded objects
Possible dwarf planets
first discovered: Ceres
Planets beyond Neptune
List of crewed spacecraft
List of probes
Outline of the Solar System
Solar System → Local Interstellar Cloud → Local
Bubble → Gould Belt → Orion Arm → Milky
Milky Way subgroup → Local Group → Virgo
Supercluster → Laniakea Supercluster → Observable
universe → Universe
Each arrow (→) may be read as "within" or "part of".
BNF: cb121153852 (data)