The Final Frontier



Type of Planet

Neptune is an ice giant, meaning a giant planet composed mainly of elements heavier than hydrogen and helium.

Ice giants consist of only about 20 percent hydrogen and helium in mass, as opposed to the Solar System's gas giants (Jupiter and Saturn), which are both more than 90 percent hydrogen and helium in mass.


The outermost layer of Neptune is the atmosphere, forming about 5-10 percent of the planet's mass, and extending up to 20 percent of the way down to its core.

Neptune's atmosphere is about 80 percent hydrogen, 19 percent helium, with small amounts of other ices, like methane, ammonia and water ice.

The winds of Neptune are the fastest in the solar system. Neptune has a giant storm much like the storm on Jupiter. This storm is often called the Great Dark Spot.

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.

At the very center of Neptune is the planet’s core. The core of Neptune is made of iron, nickel and other silicates that make up about 1.2 times the mass of the Earth.

Planetary Rings

Neptune has five rings. The rings are composed of 20-70 percent dust; the rest of the material is small rocks. The planet’s rings are difficult to see because they are dark and vary in density and size.

Size (Diameter), Mass, and Density

Neptune is 3.9 times the diameter of Earth, and 17 times the mass of the Earth.

Neptune is the densest outer planet. The density of Neptune is 1.64 grams per cubic centimeter, compared to Earth's 5.51.


Neptune is the fourth largest planet in the Solar System, but being an ice giant, Neptune is less dense than Earth. As a result, Neptune’s gravity is just 110 percent of the gravity on Earth.

Magnetic Field

Neptune has a strange magnetic field. Neptune's magnetic field is tilted 47 degrees from the planet's rotation axis.


Neptune has a freezing average temperature of -214 degrees celsius. But despite being the most distant planet, it is not as cold as Uranus. At such vast distances, however, the two ice giants take in very little heat from the Sun. Neptune's temperature is driven more by the motions within its interior than by the rays of the sun, motions that Uranus doesn't seem to share.

Length of a Day (Rotation)

A day on Neptune lasts 16 hours 17 minutes.

Axial Tilt

Neptune has an axial tilt of 28.5 degrees, which isn't too different to Earth's.

Length of a Year (Orbit)

A year on Neptune lasts 164.8 Earth years.

Distance from the Sun

Neptune is the eighth and furthest planet from the Sun, at 2,794 million miles.