Neptune
Neptune is the fourth largest planet in the solar system and the third most massive. Neptune is 17 times the mass of Earth, but just  the mass of Jupiter. Neptune is a little bit more massive than Uranus, though Neptune is denser and physically smaller than Uranus. Neptune and Uranus are often considered to be part of a sub-class of a gas giant known as "ice giants". They are smaller in size than Jupiter and Saturn, and have differences from them in composition. In the search for extrasolar planets, Neptune has been used as a reference to compare the size and structure of the discovered planet. Some discovered planets that have similar masses like Neptune are often called "Neptunes".