The ice giant, better known as Neptune, was the first planet located through mathematical predictions rather than from observing the sky.
The predicted existence of Neptune was first introduced by the French mathematician, Urbain Joseph Le Verrier. After being ignored by French astronomers he sent his theory to Johann Gottfried Galle, who later found Neptune, as predicted, in 1846.
Neptune is located nearly 4.5 billion kilometers from the sun, allowing it to orbit the sun once every 165 Earth years. Because Neptune is so far from the Earth, it is invisible to the naked eye.
Although the orbits of Pluto and Neptune intersect, they can never crash into each other because of the difference between their laps. Neptune takes three laps around the sun, while Pluto takes two. Neptune’s main axis is tipped about 47 degrees from vertical.
Neptune’s blue color is from the methane gas in its atmosphere. Methane is also responsible for the blue-green color of Uranus.
Neptune has 13 moons. Triton was the first to be discovered in 1846. Six more moons were discovered by the Voyager space probe missions. A 14th moon orbiting Neptune has been observed and is waiting to be officially recognized.
Because Neptune is the furthest planet from the sun, the temperatures on its surface are a very cold. Negative 235 degrees Celsius is not uncommon. Scientists have observed Neptune getting warmer, but they do not know why. Future missions will provide explanations.
[Sources: NASA; Associated Press]