Each time you look up to the sky and see a star you are looking at a sun in another galaxy. If you were on another planet looking back at our solar system, you would see our sun as a star.

It’s believed that every sun has planets orbiting it. Our Milky Way galaxy has more planets than it has stars.

Neptune Earth

In our solar system we have eight planets: Mercury, Venus, Earth, and Mars are the inner rocky planets. Jupiter and Saturn are the outer gas giants. Uranus and Neptune are the outer ice giants.
In recent years, astronomers have designed a new class called the “dwarf planets.” These are smaller worlds, not quite big enough to be considered a standard planet, and include Pluto. Neptune is the eighth planet from the sun.

Neptune Statistics:

  • Distance from Sun: 2.793 billion mi
  • Rings: 5
  • Radius: 15,299 mi
  • Polar Diameter: 48,682 km
  • Orbital period: 165 years
  • Mass: 1.024 × 10^26 kg (17.15 M⊕)
  • Moons: (14, including Triton)
  • Date of Discovery: September 23, 1846 by Urbain Le Verrier & Johann Galle

How did Neptune get its name:

Neptune is the eighth planet in our solar system and is known for its beautiful blue color. It was this color that was used to name it after the Roman god of the sea. The Greeks called their god of the sea, Poseidon. Neptune also has a diameter that makes it the 4th largest planet and it is third largest by mass.

Neptune wasn’t located by just using sight, but instead became the first planet found using mathematical calculations.

Urbain Le Verrier had a series of predictions that were carried forth by Johann Galle in 1946. Le Verrier suggested that the planet be named after the Roman god of the sea.


Our solar system went through a lot of changes as it was formed. Some of the larger planets are believed to have been closer to the sun and it’s thought that other bodies may have been tossed out or crashed into existing planets to merge to the ones that we know today.

Around 4 billion years ago Neptune moved from the inner area of the solar system to its current position. It wasn’t until 4.5 billion years ago that the planets finally settled to the configuration that we have now.

Structure and Surface:

Neptune is one of our solar system’s two ice giants. Both Neptune and Uranus exist in the outer solar system. Around 80% of Neptune’s mass consists of dense hot fluid of “icy” materials such as water, ammonia, and methane.

The fluids are around a rocky, small core. Neptune is considered to be one of the “giant” planets and yet is also the densest. Scientists have theorized that there might be a superhot water ocean under the cold clouds of Neptune that doesn’t boil away due to the high pressure that locks it inside.

Neptune diagram

The planet doesn’t really have a solid surface as most of its mass is made of gases.

The hydrogen, methane, and helium goes down to deep levels and merges with water and melted liquids that are over a solid core that has around the same mass as the Earth.

Neptune and Uranus have similarities when it comes to the inside of the planets. Both have two layers: a rocky core and a dense, hot liquid mantle made of water, ammonia, and methane.

The rocky core of Uranus is believed to be around 1.2 times the size of Earth’s and the mantle is thought to be between 10-15 times that of Earth’s mass.

While both Uranus and Neptune might share some characteristics and features, Uranus gives off as much heat as it receives from the sun and yet Neptune gives off around 2.61 times the heat that it gets.

This is unusual as both Neptune and Uranus have the same surface temperature.

Neptune only receives 40% of the sun’s heat energy that Uranus gets. The excess amount of internal heat is thought to be what keeps the upper atmosphere wind speeds going.

Neptune spins rather quickly and has the third shortest “day” of any planet in the solar system. Its size and rotation mean that it takes 165 Earth years for Neptune to make a full orbit around the sun.

There are 14 moons around Neptune, and the largest moon is Triton, which is shaped like a sphere and has a rotation that is opposite that of Neptune.

Scientists think that at one time in history Triton was actually a dwarf planet that Neptune caught in its gravity.

Atmosphere. Magnetosphere, and Moon Status:

Very similar to the planet Uranus, Neptune’s upper atmosphere is made up of mostly hydrogen (80%), helium (19%), and trace amounts of the methane that gives it the blue coloring.

Neptune has a much deeper shade of blue that makes it different than Uranus in atmospheric composition.

While Neptune’s ice giant neighbor, Uranus, is a blue-green color due to high levels of atmospheric methane, Neptune is mostly hydrogen and helium, giving it a brighter shade of blue.

Scientists believe that there may be an unknown element that causes Neptune to have a more intense color.

We give credit to the Voyager 2 spacecraft mission for discovering Neptune’s “Dark Spots.” These are similar to the Great Red Spot on Jupiter because they are large storms.

Additional research from the Hubble Space Telescope has shown that the storms on Neptune or “dark spots” have fairly short lives.

During the mission, Voyager 2 also found other weather patterns including a smaller, short-lived white storm that moved so fast that it was nicknamed “Scooter.”

As a gas giant, Neptune shares the same atmospheric characteristic of being divided into two bands, but Neptune’s bands have wind speeds that can reach up to 600 m/s.

At this speed Neptune has the fastest known winds of any planet within the solar system.A 1989 discovery of an oval-shaped storm in the southern hemisphere of Neptune was named its “Great Dark Spot.”

This spot is big enough to hold the entire Earth, and while this one disappeared, others have shown up on various areas of the planet.

Neptune’s magnetic field main axis is tipped to the side by around 47 degrees as compared to Neptune’s planetary rotation axis.

Both Neptune and Uranus have magnetic axis that are tilted and the tilt causes wild variations as the planet rotates. Neptune’s magnetic field is around 27 time stronger than that of Earth.

There are 13 known moons and one provisional moon around Neptune. Triton is the largest moon and was discovered in 1846, just 17 days after the discovery of the planet.

Since Neptune is the Roman god of the sea, all of the names of Neptune’s moons are for Greek mythology nymphs or lesser sea gods.

Triton holds the distinction of being the only large moon within our solar system that circles its planet in the opposite direction of the planet’s rotation.

This is called a retrograde orbit and is thought to be due to the idea that the moon was once an independent object that Neptune captured with its gravity.

Triton has surface temperatures that reach -391 degrees F/235 degrees C, and while extremely cold, Voyager 2 found geysers that spewed icy material up to 5 mi/8 km high.

Voyager also discovered that Triton has a thin atmosphere and while it has been detected numerous times since then, scientists aren’t sure why it’s getting warmer.
Neptune Methane
There are six known rings around Neptune, five are named and one remains unnamed. The named rings are Galle, Le Verrier, Lassell, Arago, and Adams.

Neptune’s rings are believed to be relatively short-lived and young, and contain unusual collections of dust that are called “arcs.” These are strange because the laws of motion indicate that they shouldn’t be in clumps but should spread out evenly.

Scientists believe that they may be affected by the gravitational effects of the moon Galatea.

There are four notable arcs in Adam, Neptune’s outer ring that have been named: Liberté (Liberty), Egalité (Equality), Fraternité (Fraternity), and Courage.

Could Life Exist on Neptune?

The extreme temperatures and pressures of Neptune are not conducive to allowing life as we know it to exist, adapt, and thrive.

Interesting Information:

While Pluto was once considered to be a planet, it has been downsized to a dwarf planet. Due to the elliptical orbit that Pluto has it is sometimes closer to both the sun and Earth than Neptune is.

One “Neptunian day” is 16 hours. That’s how long it takes for Neptune to accomplish a complete rotation. However, a Neptunian year, which is the time that it takes Neptune to orbit the sun is around 165 Earth years.

Space Missions to Neptune:

In 1989, NASA’s Voyager 2 spacecraft studied Neptune up close. This was over 140 years after the predictions made by Le Verrier about Neptune. Voyager 2 remains the first-and-only spacecraft to study Neptune, and it sent back an incredible volume of information and data about the planet and its moons.

Voyager 2 also confirmed that the ice giant had faint rings like other gas giant planets. Since that time, scientists have relied on the Hubble Space Telescope for additional information about Neptune.

Important Events:

1612: Galileo uses his small telescope and makes an error by recording Neptune as a fixed star.
1846: Through the use of only mathematical calculations, astronomers increase the number of planets in our solar system to eight as they add Neptune. The same year, they discovered Triton, Neptune’s biggest moon.
1983: Pioneer 10 becomes the first human-made spacecraft to travel beyond our solar system planets as it crosses the orbit of Neptune. The craft continues on its course as it heads to Aldebaran, a red star in the Taurus constellation, that it will pass in around 2,000,000 years.
1984: Astronomers studying Neptune discover evidence that Neptune has a ring system.
1989: Voyager 2 becomes the first and only spacecraft to visit Neptune. Voyager 2 passes Neptune at 2,983mi/4,800 km above Neptune’s north pole.
2002: Astronomers discover four additional moons orbiting around Neptune and name them: Laomedia, Neso, Sao and Halimede.
2003: Using ground-based telescopes, astronomers discover Psamathe, another new moon around Neptune.
2005: Keck Observatory scientists discover deterioration in some of Neptune’s rings.
2013: Using the Hubble Space Telescope, a scientist makes the discovery of a 14th Neptune moon and gives it the professional designation of S/2004 N 1.
2016: Using the Hubble Space Telescope scientists discover the 21st century’s first new atmospheric vortex with a dark spot on Neptune.

Facts about Neptune for Kids:

  • Neptune’s rings are so faint that prior to the Voyager 2 spacecraft mission, the rings weren’t thought to be complete. Neptune has the faintest rings of all of the gas giants.
  • Even though Neptune is a gas giant it has the second largest gravity of all of the solar system planets.
  • Neptune has a Great Dark Spot that is the size of our Earth and a Small Dark Spot that is almost the size of our moon.
  • Our ancient ancestors didn’t know that Neptune existed because it can’t be seen with the naked eye or the telescopes that they developed.
  • The coldest known object in our solar system is Neptune’s moon Triton that has temperatures on the surface that can dip down to -235 degrees C.
  • Only 17 days after the discovery of Neptune, astronomers discovered its moon Triton.

Pop Culture:

Neptune has been a frequent focus for quite a few science fiction and pop culture themes. The “Event Horizon” was a sci-fi/horror film in 1997 and Neptune was the backdrop for the storyline.

The animated series “Futurama” had Robot Santa Claus with a home based in the north pole of Neptune. The “Sleep No More” episode of Doctor Who was set on a space station that orbited around Neptune.

Star Trek: Enterprise had the episode “Broken Bow” where fans leaned that at the speed of warp 4.5 it would be possible to fly from Earth to Neptune and back in only six minutes.