10 Interesting Facts About Neptune

Neptune is the eighth planet in our solar system. It was discovered in 1846 by Johann Galle and it’s also known as the Windiest Planet. We have not visited this dark, cold, ice giant that often, but what we know will blow your space suits off!

Neptune, full view image taken by Voyager 2

This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow-angle camera. Image Credit: NASA/JPL

The Size

To start, compared to Earth, Neptune is about four times bigger. To put it in perspective if the Earth were the size of a nickel, Neptune would be about the size of a baseball.

The Distance

Neptune average distance from the Sun is 2,795,173,960 miles away. Another way to say this is that the distance from the Sun to Neptune is 30 AU. To break it down, the average distance from Earth to the Sun is 92,956,050 miles, this distance is also known as one Astronomical Unit, AU. Thus, the distance from the Sun to Neptune is 30 times more that of Earth!

One Year

Because Neptune is so far away from the Sun, it takes longer to complete one orbit. One Neptunian year is equal to 165 Earth years. Since its discovery in 1846, Neptune completed its first 165-year orbit in 2011.

The Seasons

Just like Earth and Mars, Neptune’s axis of rotation is tilted. This tilt of 28 degrees allows Neptune to experience seasons. However, since its orbit takes 165 Earth years, Neptune’s seasons last about 40 years!

Lunch at Neptune’s

Despite having seasons, it doesn’t get much warmer out there.
The light we receive on Earth is about 900 times brighter than on Neptune. It’s is so far away that even when the Sun is at high noon, it would seem like twilight for us. It takes sunlight four hours to reach Neptune.

Short Days

Just like other gas giants, Neptune’s days are quite short. It takes 16 hours to complete one rotation. Gas giants rotate really fast. For example, Uranus takes 17 hours and Jupiter takes only 10 hours. In comparison, rocky planets take longer to rotate; Mars takes 25 hours, while Mercury takes 1,408 hours which is equal to 59 Earth days.

Find out how long in one day on other planets.


Most of Neptune’s atmosphere is composed of hydrogen and helium with a little bit of methane. This mix of elements gives Neptune its unique blue color. Just like a similar mix also gives Uranus a blue-ish tint.

Neptune is one of the windiest worlds in our Solar System. They race across the planet at speeds of more than 1,200 miles per hour. Earth’s fastest winds only reach 250 miles per hour.

Neptune’s fast winds create currents, some traveling the opposite way, just like on Jupiter. These wild winds also create oval-shaped storms. Just like Jupiter’s Great Red Spot, a Great Dark Spot was discovered on Neptune’s atmosphere in 1989. Since then, it has disappeared, but numerous others have appeared and disappeared in different parts of the planet.

The planet’s mass is mostly composed of dense fluids water, ammonia and methane. Scientists believe that these fluids underneath the clouds are very hot though won’t boil away because of the high pressure of the gases keeping it all locked inside.

13 Moons

Neptune has 13 moons plus one pending official confirmation. The largest moon is called Triton, discovered by William Lassell just 17 days after the planet was discovered.

  • Triton is the only moon in the solar system that circles its planet in the opposite direction to the planet’s rotation. This suggests that Triton may have been an independent object captured by Neptune’s gravity.
    Triton, taken in 1989 by Voyager 2

    Global color mosaic of Triton, taken in 1989 by Voyager 2 during its flyby of the Neptune system. Image Credit: NASA/JPL/USGS

  • More than a century passed before Nereidi was discovered in 1949.
  • Proteus, the second largest moon, is a non-spherical moon. It is thought that Proteus’ size is the largest an object can be before its gravity pulls it into a spherical shape.
  • Proteus along five other moons were discovered until Voyager 2 visited the planet. The other five moons are Despina, Galatea, Larissa, Naiad, and Thalassa.
  • More moons were discovered in 2002 and 2003 with ground-based telescopes. Among them are Halimede, Laomedeia, Neso, Psamathe, Sao, and S/2004 N1.
  • Neso is Neptune’s most outer moon. It orbits its planet much further than any other moon in the solar system.
  • S/2004 N1 orbits between two other moons: Larissa and Proteus. It was the first satellite found in 2013 from images taken in 2004 by the Hubble Space Telescope. It will be given a formal name once its existence is confirmed.

Learn more about Neptune’s moons here.

Faint Rings

Neptune has five known rings. Starting near the planet and moving outward, they are named Galle, Leverrier, Lassell, Arago, and Adams. The rings are thought to be relatively young and short-lived.

Neptune's rigns.

These two 591-second exposures of the rings of Neptune were taken with the clear filter by the Voyager 2 wide-angle camera on Aug. 26, 1989 from a distance of 280,000 kilometers (175,000 miles). Image Credit: NASA/JPL

Voyager 2

A once in a lifetime planetary alignment allowed “for a spacecraft launched in the late 1970s to visit all four giant planets using the gravity of each planet to swing the spacecraft on to the next. This alignment occurs once every 176 years.”

Voyager 1 and Voyager 2 trajectories

Voyager 1 and Voyager 2 trajectories.

Voyager 2 was launched on August 20, 1977, followed by Vogayer 1 in on September 5, 1977. Voyager 1 and 2 visited Jupiter and Saturn, and parting ways after. Voyager 2 then reached Uranus followed by Neptune. In 1989, Voyager 2 became the first and only spacecraft to visit Neptune.
Check out this Voyager Timeline.

Resouces for Educators

  1. Solar System Exploration, Neptune.
  2. Kid Friendly Neptune.
  3. NASA Subject: Neptune
  4. Neptune Image Exploration