Pluto (134340 Pluto) is a Dwarf Planet in an eccentric orbit ranging roughly from 30 AU (Neptune's distance) to 50 AU. It has a steeper Orbital Inclination than the eight planets: 17° from the Ecliptic. It and Neptune share an Orbital Resonance, with a ratio of 3:2.
Pluto was discovered in 1930 and was considered the ninth planet until the discovery of similar objects. Five Moon's are known:
Charon's mass is 1/6 of Pluto's and its radius about 1/2 Pluto's, by far the largest moon in the Solar System compared its host planet/dwarf planet. In comparison, the Moon has 1/81 the mass and 1/4 the radius of Earth, and the Moon/Earth has been referred to as a Double Planet, since the size ratios of the other known moons to their host planets (Mars, Jupiter, etc.) are far greater.
The New Horizons mission observed Pluto during a 2015 flyby.