What is Neptune Made Of?

Neptune, like Uranus, is one of the two outer planets known as an "ice giant." Made up of more ices than Jupiter and Saturn, the chilly body almost seems to be in a class by itself.

Different images emphasize the features on Neptune. By tracking features such as the Great Dark Spot and South Polar Feature, astronomers were able to refine measurements of the length of Neptune's day. (Image credit: E. Karkoschka/The University of Arizona)

Beneath the clouds

The first layer of Neptune is its icy atmosphere, which is mostly hydrogen and helium. The bluish coloration comes from traces of methane in the air, but the planet is a more brilliant hue than the dull blue of Uranus, which implies something else could be affecting it. The enormous distance to the sun keeps the planet's temperatures low.

Neptune is the third most massive planet. Like the rest of the gas giants, Neptune has no definite surface layer. Instead, the gas transits into a slushy ice and water layer. The water-ammonia ocean serves as the planet's mantle, and contains more than ten times the mass of Earth. Temperatures inside the mantle range from 3,140 degrees Fahrenheit (1,727 degrees Celsius) to 8,540 F (4,727 F). At deep enough depths, the methane may transform into diamond crystals.

Like Earth, Neptune has a rocky core made up of iron and other metals, with a mass just greater than our planet. Temperatures in the core could reach 9,260 F (5,127 C).

Strange rings

Like the other gas giants, Neptune boasts a series of rings. But the blue planet's six rings are not as solid as its neighbors. Instead, the clumpy rings contain prominent arcs, likely due to the influence of one of Neptune's moons. Made up of ice particles and silicates, the rings are reddish.

Neptune's rings were first discovered when it passed between a star while astronomers were attempting to study the planet. The star faded out, then returned to view. Unlike other rings, the arc-like nature meant that the fading did not repeat on the other side of the planet, which puzzled scientist. It wasn't until Voyager imaged the planet in 1989 that the mystery of the rings was solved.

A tipped magnetosphere

Neptune has an unusual magnetic field which is tipped on its side in relation to the axis that the planet rotates around. The strong magnetic field, which is about 27 times more powerful than Earth's, is tipped at a 47 degree angle and is likely powered by the motions inside the mantle itself. These motions also drive strong winds and unusual weather patterns in Neptune's atmosphere.

— Nola Taylor Redd, SPACE.com Contributor

Take a look inside Neptune, the eighth planet from the Sun and has a thick atmosphere and the fastest winds in the solar system. (Image credit: Karl Tate, SPACE.com)


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Nola Taylor Tillman
Contributing Writer

Nola Taylor Tillman is a contributing writer for Space.com. She loves all things space and astronomy-related, and enjoys the opportunity to learn more. She has a Bachelor’s degree in English and Astrophysics from Agnes Scott college and served as an intern at Sky & Telescope magazine. In her free time, she homeschools her four children. Follow her on Twitter at @NolaTRedd