Neptune is a type of planet known as a gas giant. In our solar system, Jupiter, Saturn and Uranus are also gas giants. These planets are about 4 to 12 times greater in diameter than Earth and have no solid surfaces. They possess massive atmospheres that contain substantial amounts of hydrogen and helium with traces of other gases. Neptune looks blue because of methane in the atmosphere. Winds on the planet can be nine times stronger than on Earth.
Voyager 2 is the only spacecraft to have studied Neptune up close.
Image credit: NASA/JPL