|
|
Neptune is like Uranus in many ways, but has its own unique features. At a separation of about 30 astronomical units with an orbital period of 165 years, Neptune is usually the eighth planet from the Sun. However, because of Pluto's highly elliptical orbit, Neptune is at times closer to the Sun than Pluto. The full disk of Neptune in shown in the adjacent Voyager 2 image.
Neptune's diameter is about four times that of the Earth, which makes it the fourth largest planet. It is slightly smaller than Uranus, but its density is 1.6 g/cm3 (compared with 1.2 g/cm3 for Uranus), which makes it the third most massive planet. The period of rotation is about 16 hours, comparable to that of Uranus and much slower than for Jupiter and Saturn. Like the other Jovian planets, it has a ring system and a large collection of moons. The physical properties of Neptune are summarized in this table and the orbital properties in this table.