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Neptune: Quick Facts

Updated on April 26, 2019
Larry Slawson profile image

Larry Slawson received his Masters Degree in History at UNC Charlotte. He specializes in Russian and Ukrainian history.

The planet Neptune.
The planet Neptune. | Source

Planetary Properties of Neptune

Planet Name: Neptune

Orbital Semimajor Axis: 30.07 Astronomical Units (4,498 Million Kilometers)

Orbital Eccentricity: 0.009

Perihelion: 29.81 Astronomical Units (4,460 Million Kilometers)

Aphelion: 30.33 Astronomical Units (4,537 Million Kilometers)

Mean/Average Orbital Speed: 5.43 Kilometers Per Second

Sidereal Orbital Period: 163.7 Years (Tropical)

Synodic Orbital Period: 367.49 Days (Solar)

Orbital Inclination (To the Ecliptic): 1.77 Degrees

Greatest Angular Diameter (As Viewed From Earth): 2.4”

Overall Mass: 1.02 x 1026 Kilograms; Approximately 17.15 Times the Mass of Earth (If Earth = 1)

Equatorial Radius: 24,766 Kilometers; Approximately 3.88 Times the Radius of Earth (If Earth = 1)

Mean/Average Density: 1,638 Kilograms Per Meter Cubed; Approximately 0.297 Times the Density of Earth (If Earth = 1)

Overall Surface Gravity: 11.14 Meters Per Second Squared; Approximately 1.14 Times the Surface Gravity of Earth (If Earth = 1)

Escape Speed/Velocity: 23.5 Kilometers Per Second

Sidereal Rotation Period: 0.67 Days (Solar)

Axial Tilt: 29.6 Degrees

Surface Magnetic Field: 0.43 of Earth’s Overall Magnetic Field Strength (Earth = 1)

Magnetic Axis Tilt (Relative to the Rotation Axis): 46.0 Degrees

Mean/Average Surface Temperature: 59 Kelvins (-353.47 Degrees Fahrenheit)

Number of Natural Satellites (Moons): 14 Total (Discovered so far)

Neptune up close.
Neptune up close. | Source

Quick Facts About Neptune

Quick Fact #1: Neptune is the eighth planet from the Sun, and the most distant gas giant planet from the Sun. Neptune was first discovered in modern times (1846) due to the fact that it is invisible to the naked eye, making it invisible to ancient civilizations. The giant planet was first observed from an observatory in Berlin in the year 1846 by Johann Gottfried Galle. However, astronomers were aware of the planet a year earlier as mathematical models indicated the presence of an object beyond Uranus that was having a gravitational impact on the planet’s orbital patterns. Using mathematic formulas to calculate the objects trajectory, English and French mathematicians, John Couch Adams and Urbain Le Verrier, respectively, were able to pinpoint the exact region of the sky that the new planet would appear in. When Galle actually discovered the planet a year later, each of the astronomers debated who first discovered Neptune (a debate that still hasn’t been settled today). Regardless of who first discovered the planet, astronomers dubbed the new discovery “Neptune” in honor of the Roman God of the Sea.

Quick Fact #2: Out of all the planets in our solar system, Neptune has the strongest winds. At approximately 2,100 Kilometers/Hour (1,304.9 M.P.H.), the planet’s winds make Earth’s most powerful hurricanes look weak, in comparison. Scientists remain uncertain as to why the planet’s winds reach such speeds. However, it is hypothesized that Neptune’s cold temperatures allow a flow of gases throughout its atmosphere that reduces friction and, in turn, allows winds to move much faster.

Quick Fact #3: Neptune (currently) is the most distant planet from the Sun, given that Pluto is now considered a “dwarf planet.” As the scientific community continues to debate Pluto’s classification, however, this designation for Neptune may change in the near future. At approximately 2.793 billion miles from the Sun, Neptune is also the coldest planet in our solar system. In its upper atmosphere, temperatures are estimated to reach 51.7 Kelvin (or -366.6 Degrees Fahrenheit). These temperatures are three times the lowest recorded temperature on Earth (which hit a record -129 Degrees Fahrenheit).

Quick Fact #4: Like the other Jovian planets (Jupiter, Saturn, and Uranus), Neptune also possesses a ring-system; albeit, one that is quite faint and difficult to see. In contrast to Saturn’s bright and well-developed rings, however, Neptune’s five rings are not well-organized and are dark due to the presence of organic compounds. Scientists believe that the rings are composed of twenty-percent dust, and eighty-percent rock (small). The rings are named for astronomers who made crucial discoveries concerning the planet such as Galle, Le Verrier, Adams, Arago, and Lassell. Scientists are uncertain as to what created Neptune’s rings, however, it is hypothesized that they are relatively young and may have formed from the collision moons.

Quick Fact #5: Scientists believe that Neptune is composed primarily of gas (both helium and hydrogen) and ice, with a solid, rocky core. Despite the fact that the planet if much larger than Earth, its surface gravity is actually close to the gravity of Earth (only 17-percent stronger). It is hypothesized that the gravitational pull is relatively low due to the fact that Neptune’s mass is spread out over a larger surface area. Neptune remains the only planet in our solar system with a similar gravitational pull.

Quick Fact #6: In total, Neptune possesses fourteen known moons. These are Triton, Nereid, Proteus, Galatea, Despina, Thalassa, Hippocamp, Halimede, Laomedeia, Neso, Psamathe, Naiad, Larissa, and Sao. Triton is Neptune’s largest (and perhaps most interesting) moon, and is composed primarily of nitrogen, ice, and dust. Scientists believe that Triton was once a KBO (Kuiper-Belt Object) and was captured relatively recently by Neptune’s gravitational pull.

Neptune's "Great Dark Spot."
Neptune's "Great Dark Spot." | Source

Fun Facts

Fun Fact #1: Neptune’s upper atmosphere is composed primarily of 80% Hydrogen, 19% Helium, and less than 1% Methane gas. It is believed that Neptune’s deep blue coloration is the result of methane absorbing light with wavelengths that correspond to the color red.

Fun Fact #2: Similar to Jupiter’s “Great Red Spot,” Neptune also possesses dark spots which are believed to be giant storms. In contrast to Jupiter’s Great Red Spot, however, these storms are often short-lived. The first spot was discovered by Voyager-2 during its flyby decades prior. The second spot, also observed by Voyager-2 was nicknamed “Scooter,” and is also believed to be a fast-moving storm system that will eventually dissipate.

Fun Fact #3: One year on Neptune lasts approximately 165 years on Earth due to its tremendous distance from the Sun. To put its distance in perspective, it takes light approximately four hours and forty minutes to reach Neptune from the Sun. Despite these long years, one day on Neptune is remarkably short, due to its rapid rotational speed. Neptune has the third shortest day in the solar system, at only sixteen hours.

Fun Fact #4: Only one spacecraft has visited Neptune, known as Voyager-2. The spacecraft swept by the planet in 1989 and provided the first in-depth photos of the planet for NASA and the world at large. Although Neptune has been studied extensively by the Hubble Space Telescope, along with a number of ground-based observatories, there are currently no future missions planned for further exploration of the planet.

Fun Fact #5: Since its discovery in 1846, Neptune has only completed one orbit around the Sun; a feat that was accomplished in 2011.

Fun Fact #6: Triton is the only known moon in the solar system that orbits Neptune in a retrograde motion, making it a very unique object in our solar system.

“No one planet can tell us everything about the universe, but Neptune seems to hold more than its share of information about the formation of our own solar system – as well as the solar systems beyond.”

— Heidi Hammel

Quotes About Neptune

Quote #1: “No one planet can tell us everything about the universe, but Neptune seems to hold more than its share of information about the formation of our own solar system – as well as the solar systems beyond.” – Heidi Hammel

Quote #2: “If you put Earth out beyond Neptune, you wouldn’t be able to call it a planet because it couldn’t clear its zone.” – Alan Stern

Quote #3: “Neptune’s unusual behavior is showing us that though we can make great models of planetary atmospheric circulation, there may be key pieces missing.” – Heidi Hammel

Quote #4: “I grew up believing my sister was from the planet Neptune and had been sent down to Earth to kill me. I believed this because my sister Emily convinced me of it when I was a toddler.” -- Zooey Deschanel

Clouds on Neptune.
Clouds on Neptune. | Source

Formation of Neptune

Similar to the other gas giants, it has been extremely difficult for scientists to provide a model on how Neptune formed within our solar system. Current investigative models indicate that Neptune likely formed closer to the Sun, due to the lack of matter on the outer regions of the solar system during its formation. In this model, astronomers hypothesize that Neptune developed in close proximity to the Sun, where matter density was far higher, and then migrated towards the outer fringes of the solar system before being captured by the Sun’s gravitational pull. This theory, known as the “Nice Model” remains the most accepted theory for Neptune’s formation, to date, until additional data pertaining to Neptune can be uncovered by the scientific community.


Did any of these facts about Neptune surprise you?

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In closing, Neptune remains one of the most fascinating objects in our solar system. With its beautiful dark blue coloration, and mysterious allure, Neptune will continue to capture the hearts and minds of the scientific community for decades to come. What secrets does this fascinating planet hold about the formation of our solar system? What can the scientific community learn about Neptune’s composition and design? Finally, and perhaps most importantly, what can the planet Neptune tell us about the solar system and universe at large?

As NASA and the scientific community continues to delay plans for future space missions to Neptune, it is unlikely that we will be able to learn the answers to these questions in the near future. However, with the rise of private enterprises with a keen interest in space exploration, additional missions, such as Voyager-2 may become a reality sooner than we expect. Only time will tell.

Works Cited:


Choi, Charles Q. "Planet Neptune: Facts About Its Orbit, Moons & Rings." May 12, 2017. Accessed April 26, 2019.

Wikipedia contributors, "Neptune," Wikipedia, The Free Encyclopedia, (accessed April 18, 2019).

© 2019 Larry Slawson


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    • Miebakagh57 profile image

      Miebakagh Fiberesima 

      4 weeks ago from Port Harcourt, Rivers State, NIGERIA.

      Hi, Pamela, I like any other person will be much interested in this "much more information." Many thanks, and enjoy the day.

    • Pamela99 profile image

      Pamela Oglesby 

      4 weeks ago from Sunny Florida

      This is such an interesting planet, and I really liked your fun facts. when Voyager 2 takes off with its large telescope we may learn much more. I assume it will give us so much more information about most of the planet. I really liked this artcle.

    • Miebakagh57 profile image

      Miebakagh Fiberesima 

      4 weeks ago from Port Harcourt, Rivers State, NIGERIA.

      Good to note also.

    • Babu Mohan profile image

      Mohan Babu 

      4 weeks ago from Chennai, India

      Nice article Larry Slawson. It is very interesting to note Neptune has completed just one orbit around the Sun since its discovery.

    • Miebakagh57 profile image

      Miebakagh Fiberesima 

      4 weeks ago from Port Harcourt, Rivers State, NIGERIA.

      Noted. please.

    • Larry Slawson profile imageAUTHOR

      Larry Slawson 

      4 weeks ago from North Carolina

      Thank you :) Just about done with them finally haha. I'm still thinking about doing one on Earth and Pluto (even though its considered a dwarf planet now).

    • Eurofile profile image

      Liz Westwood 

      4 weeks ago from UK

      This a great fact file to add to the planet collection.

    • Larry Slawson profile imageAUTHOR

      Larry Slawson 

      4 weeks ago from North Carolina

      @lindseyburek Thank you so much! I'm really glad you enjoyed it!

    • lindseyburek profile image

      Lindsey Burek 

      4 weeks ago from Pittsburgh, Pennsylvania

      Very nice! I love reading about astronomy and this was very informative!

    • Larry Slawson profile imageAUTHOR

      Larry Slawson 

      4 weeks ago from North Carolina

      Thank you Miebakagh! I’m glad you enjoyed :)

    • Miebakagh57 profile image

      Miebakagh Fiberesima 

      4 weeks ago from Port Harcourt, Rivers State, NIGERIA.

      Hello, Larry, my pleasure in reading a useful and informative piece. Thanks for sharing.


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