The Planet Neptune

A view of Neptune from the Voyager 2 spacecraft.

Planet	Neptune
Radius (kilometers)	24764
Orbital Distance from the Sun (kilometers)	4504449769
Rotation Period (1=24 hours)	0.67125
Mass (Million Metric Tons)	1.024E+14
Density (grams/cubic centimeter)	1.64
Year Discovered	1846
Moons	13

Neptune takes over 163 Earth years to complete one orbit of the Sun - longer than any other planet.
Voyager 2 is the only spacecraft to have visited Neptune, which it flew past in August 1989.
In 1846, both John Adams of England and Urbain Le Verrier of France predicted the existence of a planet beyond Uranus based on mathematical calculations of deviations in Uranus' predicted orbit.
In 1846, using the mathematical predictions of Urbain Le Verrier, Johann Galle at the Berlin Observatory discovered Neptune.
Neptune receives less than 1/1000th the amount of sun light as does the Earth.
Neptune is the smallest of the gas giant planets.
The orbit of Neptune's moon Triton is slowly decaying and one day it will crash into Neptune
Triton is the only large moon in the solar system whose orbit is retrograde (backwards).