Neptune (Courtesy to Microsoft Encarta for this photograph.)

Neptune maintains a constant distance from the Sun almost throughout its 165 Earth year orbit. Sometimes though, Pluto makes its way into Neptune's orbit and it temporarily makes Neptune the farthest planet away from the Sun. The last time Pluto went inside Neptune's orbit was in 1979, and in 1999, Pluto went back outside Neptune's orbit again. Before the discovery of Neptune, people wondered why there were wobbles in Uranus' orbit. British astronomer John Couch Adams and French astronomer Urbain Jean Joseph Leverrier each calculated the existence and position of Neptune in 1845 and 1846. Then German astronomer Johann Gottfried Galle first looked at Neptune in 1846.

Neptune, like all the other Gas Giants, has rings. It has a total of four rings, and these rings were previously undiscovered before the Voyager missions. Many things were unknown about Neptune before the Voyager missions gave much more detailed information about Neptune. These probes detected that Neptune is made up of mainly hydrogen, helium, and small traces of methane. There is also a large storm on Neptune known as the Great Dark Spot. Like the storm on Jupiter, the Great Red Spot, it is spins around the planet at high speeds. The Great Dark Spot moves around Neptune at about 700 mph. Its size is about the diameter of the Earth. There is also a small, white storm cloud that goes around Neptune about every 16 hours. This storm is known as "The Scooter" and its true nature is still a mystery.

Scientists think that Neptune and its neighbor Uranus were made from the remains of many comet collisions. This is because much of the planet's composition is made up of comet material. Their theory is that at the time of the birth of the Solar System, Saturn was the farthest planet from the Sun. Behind Saturn, there were many comets and asteroids that were orbiting the Sun. Because all matter has gravity, the many comets collided with each other and over time the gravity brought together the planets of Uranus and Neptune. After Uranus and Neptune were formed, their combined gravity literally slingshot all of the other comets into orbit around the Sun.

Click here to continue on to the next lesson (Pluto).
Click here for a printable version of this page.