20+ Fascinating Facts About Neptune You Should Know

20+ Fascinating Neptune Facts: The planet Neptune

Spinning alone in the darkness, Neptune is located in the outer Solar System. This ice giant is made mostly of hydrogen, helium, and methane. Known for its blue color, frigid temperatures, savage winds, there are still many mysteries about Neptune. Read on to discover some interesting Neptune facts. 

Facts about Neptune

1. Neptune is the outermost planet in the Solar System.

Neptune is the eighth and most distant planet yet discovered in our Solar System (ever since Pluto was reclassified as a dwarf planet in 2006).

2. Neptune has the second least eccentric orbit of any planet in the Solar System.

Orbital eccentricity is the amount a planet’s orbit deviates from a perfect circle. If an orbit is a perfect circle, the planet’s eccentricity is zero and the more elliptical the orbit is, its eccentricity increases. 

Neptune has an eccentricity of 0.009, which is almost as low as Venus’s eccentricity (0.007). Neptune’s almost perfectly circular orbit means that on average it lies at a distance of about 4.5 billion km (2.8 billion miles) from the Sun. 

At its closest (perihelion), Neptune is 4.45 billion km (2.77 billion miles) from the Sun. At its furthest (aphelion), Neptune is 4.55 billion km (2.83 billion miles) from the Sun.

3. Neptune is the only planet in our Solar System not visible to the naked eye from Earth.

One of the more unique Neptune facts is that given its great distance from the Sun (Neptune is more than 30 times as far from the Sun as Earth) the planet can’t be seen in our night sky without a telescope.

4. Neptune is is the third-largest planet with respect to mass and is the fourth-largest in terms of diameter.

With a diameter of 49,244 km (30,598 miles), Neptune is the fourth-largest planet in the Solar System behind Jupiter, Saturn, and Uranus. Compared to Earth, Neptune is about 3.9 times wider.

With a mass of 1.02 x 1013 kg, Neptune is the third-heaviest planet in the Solar System behind Jupiter and Saturn. Neptune has 17 times as much mass compared to the Earth.

5. You could fit 57 Earths inside Neptune and still have room to spare.

The volume of Neptune is 6.25 x 1013 km3. To be precise, you could fit 57.74 Earths inside Neptune!

6. Neptune has a shorter day than we have here on Earth.

Neptune rotates at a speed of 2.68 km/s which is much faster than the speed at which the Earth rotates (0.46 km/s). In contrast to Earth’s 24-hour day, Neptune’s day is a little over 16 hours,  one-third shorter than our rotational cycle. 

This means that it takes Neptune 16 hours 6 minutes and 36 seconds for it to make one full rotation about its axis, which is what is considered a day.

7. One year on Neptune is about 165 Earth years.

While Neptune rotates faster than Earth, its orbital velocity is much slower. In fact, Neptune has the slowest orbital velocity (5.43 km/s) of all the planets in the Solar System. 

Its sluggishness means it takes Neptune a whopping 164.79 Earth years, or 60,190 Earth days, to make one trip around the Sun. If we lived on Neptune, no one alive today would have reached their first birthday!

8. It takes over four hours for the Sun’s light to reach Neptune.

It takes approximately 15,000 seconds, or 4 hours and 10 minutes for the Sun’s light to reach Neptune. In comparison, it takes 499 seconds (8 minutes and 19 seconds) for the Sun’s light to reach Earth.

9. Neptune was first observed in 1612.

The Italian polymath Galileo Galilei first spotted Neptune as early as 1612. He drew Neptune twice in his notebook as he observed the planet through his telescope. 

But because Neptune moves so slowly in its orbit, Galileo didn’t detect its motion right away and thus never recognized it as a planet, and probably thought it to be a star.

10. Neptune was the first planet whose location was predicted by using mathematics.

One of the coolest facts about Neptune is that it is so far the only planet to be discovered through mathematical predictions rather than through regular observations of the sky.

After Uranus was discovered in 1781, astronomers noticed that the planet was being tugged slightly out of its normal orbit. Working independently of one another, John Couch Adams of Britain and Urbain Le Verrier of France predicted that the gravity from a neighboring and more distant planet beyond Uranus was affecting its orbit. 

Employing mathematics, both Adams and Le Verrier figured out not only where Neptune’s position was, but also how much mass it had in the 1840s. 

11. Neptune was discovered in 1846.

Although John Couch Adams and Urbain Le Verrier had predicted the position of Neptune independently of one another, both of them had great difficulty in persuading any astronomer to actually search for the planet.

Finally, on September 23, 1846, German astronomer Johann Gottfried Galle discovered Neptune at almost exactly the position predicted by the calculations of Le Verrier.

Though there has been controversy over who should be credited in Neptune’s discovery, the honors for the discovery of Neptune are now given jointly to Galle, Le Verrier, and Adams.

On July 11, 2011, Neptune completed its first full orbit since its discovery in 1846.

12. If you weigh 100 kilograms (220 lbs) on Earth, you would weigh 114 kilograms (251 lbs) on Neptune.

Neptune has the second-highest surface gravity (11.15  m/s2) of all the planets in the Solar System, only behind that of Jupiter. The surface gravity of Neptune is 1.14 times the gravity on Earth. Hence, you would be heavier on Neptune than on Earth.

13. Neptune’s bright blue color is the result of methane in the atmosphere.

The reason why Neptune appears blue is due to the trace amount of methane in its atmosphere which absorbs the red light from the sun but reflects the blue light back into space. 

14. Neptune is named after the Roman god of the sea.

Due to its beautiful azure color, Neptune was named after the Roman god of the Sea. The astronomical symbol for Neptune is a stylized version of the god Neptune’s trident (a long three-pronged fork).

15. Neptune is one of the two so-called “ice giants.”

Along with its immediate neighbor Uranus, Neptune has been classified as one of the two so-called “ice giants” due to the abundance of ices in its atmosphere and mantle layer.

Below its heavy atmosphere, Neptune is made of layers of hydrogen, helium, and methane gases. They enclose a layer of water, ammonia, and methane – called “ices” above a small rocky core.

Neptune has no solid surface and more than 80% of the planet’s mass is made up of a hot dense fluid of these slushy “icy” materials deeper inside. However, Neptune’s water is not drinkable since the chemical reactions with the rock would make the liquid water salty.

16. Neptune is the windiest planet in the Solar System.

One of the most mindblowing facts about Neptune is that it has the strongest winds in the Solar System. Winds reaching speeds of 2,100 km/h (1,300 mph) have been recorded on Neptune which is more than 1.7 times the speed of sound.

17. Neptune experiences similar seasonal changes to Earth but the long orbital period of Neptune means that the seasons last for over forty Earth years.

Similar to Earth, Neptune’s axis of rotation is tilted with respect to the plane of its orbit around the Sun. This tilt (∼28°) allows Neptune to experience seasons but the planet’s long orbital period means that the seasons last for 41 Earth years!

18. The dwarf planet Pluto spends 20 years out of its entire 248-year orbit within Neptune’s orbit.

Pluto, which was considered a planet until it was reclassified as a dwarf planet in 2006, experiences a very erratic, oval orbit. For about 8% of its orbit (20 years), Pluto is actually closer to the sun than Neptune.

The last time that Pluto was within Neptune’s orbit was from 21 January 21, 1979, to February 11, 1999. Sadly none of us will be around when Pluto next repeats this process as it won’t happen again until September 2226!

Because their orbits are steeply inclined to one another, Pluto and Neptune can’t collide. When Pluto crosses into Neptune’s orbit, it is actually well below the plane that Neptune orbits in.

19. Only one spacecraft has flown by Neptune.

The only spacecraft to have flown by Neptune was NASA’s Voyager 2 spacecraft in 1989. It captured the first close-up images of the planet. 

It took 4 hours and 6 minutes to send the signals from Voyager 2 back to Earth.

20. Neptune has five faint rings around it.

Though they aren’t as striking as the ones you see in orbit around Saturn, Neptune has five known rings, but they are thin and barely visible. Starting near the planet and moving outward, they are named Galle, Le Verrier, Lassell, Arago, and Adams. 

The rings are formed of clumps of dust and debris and are thought to be relatively young. It is speculated that the rings formed when one of Neptune’s inner moons got too close to the planet and was torn apart by gravity.

21. Neptune has a very active climate.

Despite being so far-flung from the Sun, Neptune’s climate is anything but bland. Neptune is very unique with its weather conditions because storms can appear so suddenly and disappear just as quickly.

In 1989, Voyager 2 tracked a large, oval-shaped, dark storm in Neptune’s southern hemisphere. This “Great Dark Spot,” which was large enough to contain the entire Earth, spun counterclockwise and moved westward at almost 1,200 km (750 miles) per hour. 

Subsequent images taken by the Hubble Space Telescope in 1994 showed no sign of this Great Dark Spot. Numerous other maelstroms have appeared and disappeared in different parts of the planet.

22. Neptune has 14 known moons.

One of Neptune’s moon remains unnamed. The other 13 are named after sea gods and nymphs in Greek mythology. Neptune’s named moons are: 

  • Naiad 
  • Thalassa
  • Despina
  • Galatea 
  • Larissa
  • Proteus
  • Triton
  • Nereid
  • Halimede
  • Sao
  • Laomedeia
  • Psamathe
  • Neso

The largest of Neptune’s moons is Triton and comprises more than 99.5% of the mass in orbit around Neptune. Possessing an average surface temperature of -235°C (-391°F), it is one of the coldest known bodies in our solar system.

Triton is the seventh-largest moon in the Solar System and the only large one that circles its planet in a direction opposite to the planet’s rotation (a retrograde orbit). This hints that it may once have been an independent object of the Kuiper Belt that Neptune captured.

23. The magnetic field of Neptune is 27 times more powerful than that of Earth’s.

The main axis of Neptune’s magnetic field is tipped over by about 47 degrees compared with the planet’s rotation axis. This misalignment means that Neptune’s magnetosphere undergoes wild fluctuation each time the planet completes one rotation.


1. NASA: Neptune In Depth

2. NASA: Neptune Fact Sheet

3. Encyclopedia Britannica