Neptune facts: Information about Planet Neptune

Big blue planet Neptune is the 4th largest planet in our Solar System, but some lesser known Neptune facts are that it has rings and that it has a moon with the potential to harbor life.

Read on to learn more about Neptune, its little-know rings and it’s intriguing moon, Triton.

Neptune: Ice Giant

Like Jupiter and Saturn, Neptune and Uranus are considered giant – or jovian – planets. The four jovian planets are further divided into groups: gas giants and ice giants. Due to their remarkable similarity, Neptune and Uranus are classified as ice giants. The name refers to the various ices present in the mantle of the planet. In comparison to the gas giants, the ice giants also contain less hydrogen and helium and more heavier elements, such as oxygen, carbon and nitrogen.

As astronomers have discovered exoplanets – planets outside our solar system – we’ve learned that our ice giants are not unique. In fact, they’re most likely abundant in the universe.

Although Neptune was officially discovered in 1846, there is some debate whether Galileo was actually the first to observe the planet in 1613.

How big Is Neptune?

With a diameter of 49,244 km, Neptune is the fourth largest planet in our solar system and approximately 3.9 times as big as Earth. Although Neptune is the smallest of the giant planets, it’s considerably more massive than Uranus. With a mass of 1.0241 x 1026 kg, it’s the third most massive planet in the solar system. In comparison to Earth, Neptune is approximately seventeen times more massive.

What is it like on Neptune?

The structure of Neptune can be divided into roughly three areas: atmosphere, mantle, and core. The planet’s atmosphere can be further divided into the lower troposphere, the stratosphere, the thermosphere and the exosphere.

Due to the extreme pressure and heat involved, the science involved in predicting the exact nature of the various layers of Neptune is highly theoretical, particularly with respect to the planet’s mantle and core.

facts about Neptune
Neptune image from NASA’s Voyager 2 (NASA/JPL)

What is Neptune made of?

Neptune’s atmosphere is composed primarily of hydrogen and helium. A small amount of methane exists in the planet’s upper atmosphere giving it its blue colour. Astronomers currently believe Neptune’s mantle is composed of water, ammonia and and methane ices.

Although astronomers strongly believe Neptune has a solid core, we don’t have the technology to penetrate the upper layers of the planet’s atmosphere. Even though we don’t know its exact nature and composition, the core is presently believed to be a mixture of rock and ice.

Planetary features of Neptune

Like the other giant planets, Neptune has no visible surface features. What the planet does have is notable atmospheric features in the form of storms. These violent storms are massive and often referred to as dark spots or ovals. Lasting years, the storm systems on Neptune are relatively long lived; however, they’re not permanent features like Jupiter’s Great Red Spot.

Despite its distance from the Sun, Neptune has a internal heat source. Although what creates this heat source is a mystery, astronomers believe it drives Neptune’s turbulent storm system. In comparison, Uranus is much more non-descript planet – most likely because it lacks a similar internal heat source.

Is there life on Neptune?

Due to the inhospitable conditions on the planet – including extreme temperature, pressure and weather – scientists do not believe there is life on Neptune. If life did exist on the planet, it would not be life as we know it. Noted scientists Carl Sagan and Stephen Hawking have theorised how life could develop on the giant planets, but these musings are science fiction for the time being.

Some astronomers theorise that there is a small chance that Neptune holds liquid oceans beneath its dense atmosphere – or could at least could in the future. If liquid water oceans did exist on the planet, the likelihood of Neptune harbouring life would increase exponentially.

Does Neptune have rings?

Like the other giants, Neptune has a ring system. First observed from Earth in 1984, the rings were later confirmed during the Voyager 2 mission to the planet.

The planet has five rings (listed in order from closest to furthest from Neptune): Adams, Arago, Lassell, Le Verrier and Galle. These rings are not uniform in width: Some of them contain thicker portions which are better described as arcs. In addition, the planet has an unnamed partial ring in the same orbit as Galatea, one of Neptune’s moons. Astronomers suspect that Neptune’s rings are composed of “ices with some silicates and carbonaceous materials.”

In comparison to Saturn’s majestic ring system, Neptune’s rings are thin and faint. Unfortunately, the rings cannot be seen from Earth with consumer-level telescopes due to their thinness, their lack of reflectivity and the distance to Neptune.

What missions have visited Neptune?

Voyager 2 is the only mission to reach Neptune so far. The probe performed a flyby of the planet, passing as close as 5,000 km, on August 25, 1989. Much of what we now know about Neptune and its moon system can be attributed to that brief flyby. Before heading out on its interstellar mission, Voyager 2 recorded images and took measurements of the planet, revealing an atmosphere with surprising activity, including the Great Dark Spot, a large, long-lived storm system. The probe also flew by Triton, discovered four new moons and confirmed the existence of one more.

Planned expeditions to Neptune

Could there be future missions to Neptune in store? Although there is currently nothing planned, Neptune and Uranus are both possible destinations for future missions. The prospect of further investigating its moon Triton makes Neptune a more interesting destination than its nearer ice-giant twin. Space agencies continue to examine the feasibility of missions to these outer planets, and missions to the Neptunian system continue to be proposed for funding.

Does Neptune have moons?

Neptune has fourteen known moons, including Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, Nereid, Halimede, Sao, Laomedeia, Psamathe, and Neso. Neptune’s fourteenth moon, which has not yet received its official name, was discovered in 2013 and orbits between Larissa and Proteus.

Apart from Triton – one of the largest and most interesting moons in the solar system – Neptune’s moons are small, irregular shaped and unremarkable.

Although Neptune has many more moons than inner planets like Earth and Mars, some wonder why the Neptunian system does not include as many moons as the Saturnian and Jovian systems. Some scientists postulate that Triton disrupted a larger moon system when it was captured billions of years ago.

Triton neptune moon
Triton, taken by Voyager 2 in 1989 (NASA/JPL)

Triton: Neptune’s most fascinating moon

Triton is one of the most remarkable moons in our solar system. It’s also an object of interest to astronomers due to the nature of its atmosphere, the mystery of its origin, its volcanic activity and its life-bearing potential.

Triton is also one of very few moons with an atmosphere. Although there are multiple moons with atmospheres, including our own moon, only Triton, Io and Titan have significant atmospheres. However, when not compared to other moons, Triton’s atmosphere is thin: only 1/70,000th as thick as our own.

The surface of Triton is extremely cold – the average temperature is minus 235 Celsius – and covered in frozen nitrogen and water. Unlike our static moon, Triton is one of very few moons that exhibits volcanic activity.

Triton has also tantalized scientists due to its life-bearing potential. Many astronomers suspect that a liquid ocean of water may lay beneath Triton’s icy crust. In addition to the presence of water, astronomers are intrigued by the existence of organic compounds called tholins on the moon’s surface.

Neptune facts – key statistics

  • Distance from Earth: 4,498 million km
  • Distance from the Sun: 4,351 million km
  • Temperature: –214 deg C
  • Mass: 1.0241 x 1026 kg (17.148 x Earth)
  • Surface area: 7.6183 x 109 km2 (14.980 x Earth)
  • Volume: 6.25257 x 1013 km3
  • Diameter: 49,244 km
  • Radius: 24,622 km
  • Orbital period: 16.11 hours


Further information

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