|FactSnippet No. 1,002,425|
40 Facts About Pluto
Pluto is the ninth-largest and tenth-most-massive known object to directly orbit the Sun.
|FactSnippet No. 1,002,426|
Pluto has five known moons: Charon, the largest, whose diameter is just over half that of Pluto; Styx; Nix; Kerberos; and Hydra.
|FactSnippet No. 1,002,427|
Pluto's 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.
|FactSnippet No. 1,002,428|
Once Pluto was found, its faintness and lack of a viewable 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.
|FactSnippet No. 1,002,429|
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.
|FactSnippet No. 1,002,430|
Lowell had made a prediction of 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.
|FactSnippet No. 1,002,431|
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.
|FactSnippet No. 1,002,432|
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.
|FactSnippet No. 1,002,433|
Pluto argued that all big spherical moons, including the Moon, should likewise be considered planets.
|FactSnippet No. 1,002,435|
Pluto stated that because less than five percent of astronomers voted for it, the decision was not representative of the entire astronomical community.
|FactSnippet No. 1,002,436|
The resolution asserted that Pluto was "unfairly downgraded to a 'dwarf' planet" by the IAU.
|FactSnippet No. 1,002,438|
In contrast, Pluto's orbit is moderately inclined relative to the ecliptic and moderately eccentric .
|FactSnippet No. 1,002,439|
When Pluto is closest to the Sun, and close to Neptune's orbit as viewed from above, it is the farthest above Neptune's path.
|FactSnippet No. 1,002,440|
Pluto's orbit passes about 8 AU above that of Neptune, preventing a collision.
|FactSnippet No. 1,002,441|
However, it is not agreed upon among astronomers whether Arawn should be classified as a quasi-satellite of Pluto based on this motion, since its orbit is primarily controlled by Neptune with only occasional smaller perturbations caused by Pluto.
|FactSnippet No. 1,002,443|
Plains on Pluto's surface are composed of more than 98 percent nitrogen ice, with traces of methane and carbon monoxide.
|FactSnippet No. 1,002,444|
Pluto's surface is quite varied, with large differences in both brightness and color.
|FactSnippet No. 1,002,445|
Pluto is one of the most contrastive bodies in the Solar System, with as much contrast as Saturn's moon Iapetus.
|FactSnippet No. 1,002,446|
Pluto's color is more similar to that of Io with slightly more orange and significantly less red than Mars.
|FactSnippet No. 1,002,447|
In June 2020, astronomers reported evidence that Pluto may have had a subsurface ocean, and consequently may have been habitable, when it was first formed.
|FactSnippet No. 1,002,448|
In March 2022, they concluded that peaks on Pluto are actually a merger of "ice volcanoes", suggesting a source of heat on the body at levels previously thought not possible.
|FactSnippet No. 1,002,449|
Pluto is more than twice the diameter and a dozen times the mass of Ceres, the largest object in the asteroid belt.
|FactSnippet No. 1,002,450|
Determinations of Pluto's size have been complicated by its atmosphere and hydrocarbon haze.
|FactSnippet No. 1,002,451|
Pluto has a tenuous atmosphere consisting of nitrogen, methane, and carbon monoxide, which are in equilibrium with their ices on Pluto's surface.
|FactSnippet No. 1,002,452|
Pluto has no or almost no troposphere; observations by New Horizons suggest only a thin tropospheric boundary layer.
|FactSnippet No. 1,002,453|
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 .
|FactSnippet No. 1,002,454|
Orbital periods of all Pluto's moons are linked in a system of orbital resonances and near resonances.
|FactSnippet No. 1,002,455|
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.
|FactSnippet No. 1,002,456|
The similarity in size of Charon and Pluto has prompted some astronomers to call it a double dwarf planet.
|FactSnippet No. 1,002,457|
Pluto's moons are hypothesized to have been formed by a collision between Pluto and a similar-sized body, early in the history of the Solar System.
|FactSnippet No. 1,002,458|
One early hypothesis was that Pluto was an escaped moon of Neptune knocked out of orbit by Neptune's largest current moon, Triton.
|FactSnippet No. 1,002,459|
Eris is about the same size as Pluto but is not strictly considered a member of the Kuiper belt population.
|FactSnippet No. 1,002,461|
For example, eclipsing a bright spot on Pluto makes a bigger total brightness change than eclipsing a dark spot.
|FactSnippet No. 1,002,462|
Equatorial region of the sub-Charon hemisphere of Pluto has only been imaged at low resolution, as New Horizons made its closest approach to the anti-Charon hemisphere.
|FactSnippet No. 1,002,463|
Map of Pluto based on Hubble images from 1996, centered on the anti-Charon hemisphere, covering the southern hemisphere down to 75°S.
|FactSnippet No. 1,002,464|