Neptune is the farthest from the Sun among the eight recognized planets. It is the Solar System’s eighth planet, orbiting at an average distance of about 30.1 astronomical units, where one astronomical unit is Earth’s average distance from the Sun.
Neptune is an ice giant, not a gas giant like Jupiter or Saturn. Its atmosphere is mostly hydrogen and helium with methane, which absorbs red light and contributes to Neptune’s blue appearance. It takes about 164.8 Earth years to complete one trip around the Sun.
Pluto is the usual source of confusion. The International Astronomical Union classified Pluto as a dwarf planet in 2006, so it is not one of the eight recognized planets. Pluto’s elongated orbit also carried it inside Neptune’s orbit from 1979 to 1999, meaning “farthest” can depend on whether one includes dwarf planets and on the date.
Neptune was discovered in 1846 after astronomers predicted its position from irregularities in Uranus’s orbit. It is slightly smaller than Uranus but more massive and denser.