Neptune
Neptune is the eighth and farthest-known Solar planet from the Sun. It is 17 times the mass of Earth. It is referred to as one of the solar system's two ice giant planets (the other one being its near-twin Uranus). Being composed primarily of gases and liquids, it has no well-defined "solid surface." The planet orbits the Sun once every 164.8 years at an average distance of 30.1 AU (4.5 billion km; 2.8 billion mi). Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation.
