Is Neptune Mostly Made of Gas?

By Susan Sherwood; Updated April 24, 2017
Neptune’s five rings are rock and dust, not gas.

Although the outer planets have traditionally been called “gas giants,” Neptune and its neighbor Uranus have more recently been nicknamed “ice giants.” As scientists discover more about Neptune, they are finding that the composition of the planet is less gaseous and more slushy.

What's Out There

Neptune’s atmosphere accounts for 5 to 10 percent of its mass. Much of it is icy. Eighty percent of the atmosphere is hydrogen, while most of the rest is helium. A small amount of atmospheric methane reflects red light, causing the planet to appear bright blue.

Under the Atmosphere

Neptune’s core has more mass than the entire Earth. Most likely, it is liquid rock composed of elements such as iron and nickel. Above the core is the mantle. On Neptune this area is liquid rather than gas or solid. The ocean-like mantle is the largest of Neptune’s layers. It is composed of hydrogen, helium and water, with small amounts of ammonia and methane.

About the Author

Living in upstate New York, Susan Sherwood is a researcher who has been writing within educational settings for more than 10 years. She has co-authored papers for Horizons Research, Inc. and the Capital Region Science Education Partnership. Sherwood has a Ph.D. in curriculum and instruction from the University at Albany.