Diameter: 49528 km
SMA: 30.1037 AU
Period: 164.9041 years
Eccentricity: 0.011214
Rotation: 0.6713 days
Inclination: 1.8°
Axial tilt: 28.3°

Mass: 1.02413x10²⁴kg
Density: 1638 kg/m³
Gravitation: 11.15 m/s²
Escape velocity: 23.5 m/s
Orbit velocity: 5.48 km/s (mean)

Moons: 14
74% hydrogen, 25% helium, 1% methane
gaseous

The ice giant Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. (Galileo had recorded it as a fixed star during observations with his small telescope in 1612 and 1613.) When Uranus didn't travel exactly as astronomers expected it to, a French mathematician, Urbain Joseph Le Verrier, proposed the position and mass of another as yet unknown planet that could cause the observed changes to Uranus' orbit. After being ignored by French astronomers, Le Verrier sent his predictions to Johann Gottfried Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Seventeen days later, its largest moon, Triton, was also discovered.

Nearly 4.5 billion km (2.8 billion miles) from the Sun, Neptune orbits the Sun once every 165 years. It is invisible to the naked eye because of its extreme distance from Earth. Interestingly, the highly eccentric orbit of the dwarf planet Pluto brings Pluto inside Neptune's orbit for a 20-year period out of every 248 Earth years. Pluto can never crash into Neptune, though, because for every three laps Neptune takes around the Sun, Pluto makes two. This repeating pattern prevents close approaches of the two bodies.