Pluto, which is no longer classified as a planet, is the largest object in the Kuiper belt. It is also the tenth most massive body observed directly orbiting the sun. In 2014, it was 32.6 AU from the Sun.

Comparable to other objects in the Kuiper belt, Pluto is composed primarily of rock and ice. After Eris, it is also the second most massive known dwarf planet. It is moderately small, roughly one-sixth the mass of the Moon and one-third its capacity. It has an unconventional and extremely disposed orbit that takes it from 30 to 49 AU (4.4-7.4 billion km) from the Sun. This causes Pluto to sporadically come closer to the Sun than Neptune, but a ring road reverberation with Neptune averts the bodies from bumping.

Pluto was initially categorized as the ninth planet from the Sun and was discovered in 1930. Its rank as a key planet fell into question succeeding further study of it and the outer Solar System over the ensuing 75 years. With the discovery of the minor planet 2060 Chiron starting in 1977, several icy objects similar to Pluto with bizarre orbits were found. The most remarkable was the scattered discus object Eris which is 27 percent more massive than Pluto and was discovered in 2005.

Pluto's discovery made headlines across the globe. After the god of the netherworld, the name Pluto was proposed by Venetia Burney, an eleven-year-old lass in Oxford, England, who was fascinated in orthodox mythology. She proposed it in a discussion with her grandfather Falconer Madan, a former librarian at the University of Oxford's Bodleian Library, who handed the name to astronomy professor Herbert Hall Turner, who cabled it to associates in the US.

The comprehension that Pluto is only one of some large icy bodies in the outer Solar System impelled the International Astronomical Union (IAU) to officially define what it means to be a "planet" in 2006. The definition excluded Pluto and re-categorized it as a member of the new "dwarf planet" classification and unambiguously as a plutoid.

Astronomers who clash with the decision hold that Pluto should have stayed classified as a planet, and other dwarf planets and moons should be added to the planets' list along with Pluto. Pluto has five known moons namely, Charon, Nix, Hydra, Kerberos, and Styx. Pluto and Charon are occasionally defined as a binary system because the barycenter of their circuits does not lie within either body. Charon is officially classified as one of the largest Pluto's moon.

The Pluto system is due to be visited by spacecraft for the first time on July 14, 2015. The New Horizons investigation will execute a flyby during which it will try to take comprehensive measurements and images of the plutoid and its moons.

Harvard University held an unceremonious public discussion about Pluto's status in the fall of 2014. The three presenters were the former chair of the International Astronomical Union, Dr. Owen Gingerich, associate director of the Minor Planet Center, Dr. Gareth Williams, and director of the Harvard Origins of Life Initiative, Dr. Dimitar Sasselov. The spectators elected favorable to reestablish Pluto as a planet.