Pluto

This object is a former planet.

This object was once classified as a planet, but has since been demoted due to further scientific study.

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Pluto
True color image of Pluto, by New Horizons during its flyby of Pluto in 2015.
Discovery Data
Discovered By	Clyde Tombaugh
Discovered On	February 18, 1930
Discovery Site	Lowell Observatory
Physical Characteristics
Diameter	2376.6 km
Mass	0.0022 of Earth's
Density	1.854 g/cm3
Number of Moons	5
Volume	0.0065 of Earth’s
Axial Tilt	122.5°
Albedo	0.5
Rotational Period	6.4 days
Temperature	-229°C
Atmospheric Data
Atmospheric Composition	Nitrogen, Methane, and Carbon Monoxide.
Orbital Characteristics
Orbital Period	248 years
Semi-Major Axis	5906380000 km
Perihelion	4436820000 km
Aphelion	7375930000 km
Escape Velocity	1.21 km/s
Eccentricity	0.25
Inclination	17.14°

Pluto, minor planet designation (134340) Pluto is the second closest dwarf planet to the Sun, formerly known as the ninth planet. It was discovered on February 18, 1930 by astronomer Clyde W. Tombaugh. It is the largest object in the Kuiper belt but less dense than Eris. It was originally referred to as the ninth planet, but was demoted into being classified as a dwarf planet in 2006.

Pluto's natural satellite, Charon, is half the size of Pluto. In fact, it is so big that Pluto orbits Charon too. But the IAU has yet to formalize a definition for a binary dwarf planet system, so Charon is classified as a satellite for now.

Moons

Main article: Moons of Pluto

Pluto has 5 natural satellites. Charon, Nix, Kerberos, Hydra, and Styx. Charon is half of Pluto's diameter.

Interior

Interior of Pluto (model 1)

The outer crust of Pluto is made of frozen nitrogen and water ice. Under the crust is either a frozen layer of water or liquid water. The final layer is the middle of Pluto, a silicate core.

Formation

Pluto was formed from a clump of rocky materials and particles around 4.5 billion years ago between the location of Neptune and Uranus.

It propelled to the edge of the Solar System during the Migration of Neptune event as Jupiter's and Saturn's gravity propelled Neptune towards the edge of the Solar System.

Surface

Not much is known about Pluto's surface.

Scientists theorize hydrocarbon atoms form when the Sun's light rays hit Pluto's surface, which could explain why Pluto's snow looks a bit reddish-brown. However, artist depictions describe Pluto's surface as being a bumpy place being made of rock. Pluto has numerous caverns and mountainous areas.

Atmosphere

Atmosphere of Pluto, taken by New Horizons.

Pluto does not have a significant atmosphere. It has a thin envelope of gas that is most likely made up of nitrogen, methane, and carbon monoxide, that develops in equilibrium with solid nitrogen and carbon monoxide ices on the surface as it approaches the Sun. As Pluto moves away from its perihelion (closest point to the Sun), more of its atmosphere freezes and falls to the ground. When it returns to a closer proximity to the Sun, the temperature of Pluto's solid surface will increase, causing the nitrogen ice to sublimate into gas—creating an anti-greenhouse effect. Much as sweat evaporating from the surface of human skin, this sublimation has a cooling effect and scientists have recently discovered, by use of the sub-millimeter array, that Pluto's temperature is 10 kelvin less than they expected.

Gallery

Geology of Pluto
Regions	Belton • Tombaugh "The Heart" • Lowell
Terrae	Hayabusa • Pioneer • Venera • Viking • Voyager
Maculae	"Brass Knuckles" (Krun • Ala • Balrog • Vucub-Came • Hun-Came • Meng-pʻo) • Cadejo • Morgoth
Hills and Mountains	Challenger Colles • Coleta de Dados Colles • Hillary Montes • Tenzing Montes
Plains	Sputnik Planitia
Valleys and Depressions	Quidlivun Cavus
Lineaea	Luna Linea
Craters	Bower • Burney • Brinton • Coradini • Coughlin • Edgeworth