|Diameter|| 2,374 km|
|Distance from the Sun|| 5.9 billion km|
3.67 billion miles
|Discovered by||Clyde W. Tombaugh|
|Discovery date||February 18, 1930|
Pluto (minor planet designation: 134340 Pluto) is the second-most-massive known dwarf planet in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun. Although Pluto was discovered in 1930, limited information on the distant object delayed a realistic understanding of its characteristics. Pluto is the second largest known dwarf planet and tenth largest orbiting the Sun. From its time of discovery in 1930 to 2006 it was considered to be the ninth planet in the solar system, but because additional objects have been discovered including Eris which is 27% more massive, the IAU reclassified Pluto and the other objects as dwarf planets.
Pluto was the Roman god of the underworld and the judge of the dead. Pluto is an alternative name for the Greek god Hades, but was more often used in Roman mythology in their presentation of the god of the underworld.
On February 18, 1930, Tombaugh discovered the tiny, distant planet by use of a new astronomic technique of photographic plates combined with a blink microscope.
Pluto takes 248 Earth years for Pluto to complete one orbit around the Sun. Its orbital path doesn't lie in the same plane as the eight planets, but is inclined at an angle of 17°. Its orbit is also more oval-shaped, or elliptical, than those of the planets.
Pluto is thought to be made of mostly ice. It probably also has a small rocky core which might contain some metals. The ice on the surface of Pluto is made of frozen nitrogen, methane and carbon monoxide.
When Pluto is closer to the Sun in its orbit, the warmth from the Sun heats up the frozen ices of nitrogen, methane and carbon monoxide on Pluto's surface. These ices vaporize and form a temporary atmosphere. When Pluto moves farther from the Sun, the atmosphere freezes and falls back onto Pluto's surface.
Pluto has five moons down to a detection limit of about 1 km in diameter. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, and Hydra. Charon, the largest of the five moons, is mutually tidally locked with Pluto, and is massive enough that Pluto–Charon is sometimes considered a double dwarf planet.
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. 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 on July 14, 2015.