Neptune is the fourth largest of the planets in the solar system, and eighth planet in order of increasing distance from the sun. Neptune is, on average, about 4.5 billion km from the sun. It is about 49,400 km in diameter, or about 3.8 times as wide as the earth. Even though Neptune's volume is 72 times that of Earth's, its mass is only 17 times Earth's mass. Like Jupiter and Saturn, Neptune is one of the "gas giant" planets, composed of a deep atmosphere around a liquid surface and sometimes a solid core. Neptune's atmosphere consists of mostly hydrogen and helium, but up to three percent of Neptune's atmosphere is made of methane, which gives the planet its striking blue color. Its core contains more rock and metal than the cores of other gas giant planets. Neptune has a magnetic field, which is tilted more than 50° to the rotation axis. Neptune rotates completely on its axis once every 16 hours and orbits the sun once in 164.79 Earth years.

Characterstics of Neptune: