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Definition of Neptune

Neptune is the eighth and also the farthest planet from the Sun in the Solar System. It is the fourth-largest planet in terms of diameter, the third-most-massive planet, and the densest giant planet. Neptune has 17 times more mass than Earth, it is more massive than its near-twin Uranus. Neptune is a dense and small planet because its greater mass causes more gravitational compression of its atmosphere. This plant is named after the Roman god of the sea. This planet cannot be seen to the naked eye. It is the only planet in the Solar System which is found by mathematical prediction rather than by empirical observation.

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Neptune was observed by Galileo Galilei in 1613. He thought that it was a star but when he wanted to further research it, the motion of the planet began to be far too slight to be detected again. The greatest factor in the discovery of Neptune was the planet Uranus, whose orbit astronomers were calculating. They observed that Uranus wasn’t following their models.

The perturbed orbit of Uranus forced the astronomers to conclude that another undiscovered planet must be at fault. They predicted where it should be, and the astronomer, Urbain Le Verrier, asked the help of Johann Galle. He found the planet one degree away from the predicted point thus making Neptune the first planet to be discovered by mathematical calculations and predictions.

Distance, Size, and Mass of Neptune

Neptune is at an average distance of 2.8 billion miles/4.5 billion kilometers away from the Sun. It’s currently 29.4 AU away from the Earth with its light taking up to 4 hours to arrive at us. It has an equatorial radius of 15.387 miles or 24.764 kilometers and a diameter of 49.244 km or 30.598 mi. It’s the fourth-largest planet of the Solar System.

Orbit and Rotation of Neptune

As it is the farthest planet from the Sun, it has the longest orbital duration which completes a revolution around the Sun in about 165 years. However, one rotation on Neptune is completed in 16.11 hours. The average distance from the Sun is about 30.1 AU, at its perihelion 29.81 AU, and its aphelion 30.33 AU. The elliptical orbit of Neptune is inclined 1.77° when comparing to that of Earth.

Atmosphere and Climate of Neptune

The atmosphere in Neptune is made up of hydrogen, helium, and methane. Although Neptune is not as cold as Uranus, it has the most powerful winds despite being the furthest planet from the Sun and receiving the lowest energy from it. It has the wildest and strangest weather. There is an average temperature of -214 degrees Celsius in Neptune. Wind speeds blowing westward on the equator reach up to 2,160 kilometers per hour, nearly a supersonic flow. Bands and colossal storms are also formed on this planet.

Moons/Satellites of Neptune

The first and the largest moon discovered was Triton, just 17 days after Neptune itself was discovered. A total of 14 known moons surround Neptune. All of them are named after water deities in Greek mythology. They can be divided into regular, irregular, and unusual irregular moons.

Regular moons- Out of all the 14 moons, 7 are inner regular moons which means that they orbit along Neptune’s ecliptic with circular orbits or orbits with low eccentricity. In order of their distance from Neptune, they are classified as Naiad, Thalassa, Despina, Larissa, Hippocamp, and Proteus.

Irregular moons- The rest of the 7 moons are irregular moons. They follow an inclined, eccentric, and retrograde orbit. In order of their distance, they are classified as Triton, Nereid, Halimede, Sao, Laomedeia, Psamanthe, and Neso.

Did You Know?

  • The name Neptune was first given to the seventh planet of the Solar System, Uranus. Although the name was discarded, Uranus ultimately helped in the discovery of the eighth planet, which would bear the name Neptune.

  • In 2011, Neptune completed its first 165-year orbit since it was discovered in 1846. It means that just 1 Neptunian year has been witnessed.

  • Between 2013 to 2049, the closest approach of Neptune and Earth will happen in 2041 at a distance of 28.8 AU.

  • Due to the dwarf planet Pluto’s elliptical orbit, it is sometimes closer to the Sun and Earth than Neptune. 

  • Neptune is 30 times farther than Earth’s orbit is from the sun.

  • The Sun is 900 times dimmer on Neptune than it is on Earth.

  • Neptune has its gravity at 1 bar of 11.15 m/s2, 1.14 times the surface gravity of Earth, and is surpassed only by Jupiter who has a gravity of 24.79 m/s².

  • Neptune possesses a very strong magnetic field which is around 27 times stronger than that on Earth.

FAQ (Frequently Asked Questions)

1. Why is Neptune Blue?

Neptune is mainly composed of gases one percent methane, nineteen percent helium, and around eighty percent hydrogen. Its blue color is due to the presence of methane. When sunlight hits Neptune’s surface, methane clouds absorb the red end of the spectrum of visible light. The blue part of the spectrum is reflected back. When the bright bluish color of Neptune is seen, the reflected sunlight, minus the red light is actually seen. Scientists have discovered a few thin, colored bands around Neptune, indicating that it accurately resembles a heavenly blue gaseous sphere along with a faint splash of colored rings.

2. How is the Structure of Neptune?

The internal structure is very similar to the structure of Uranus. Its atmosphere forms 5% to 10% of its mass and it extends about 10% to 20% towards the core reaching pressures of about 10 GPa. Concentrations of methane, ammonia, and water are mostly found in the lower regions of the atmosphere. The conditions can be such that even methane decomposes into diamond crystals which rain downwards like hailstones. The core is mostly composed of iron, nickel, and silicates. The core is estimated to be about 1.5 times the mass of the Earth. The pressure at the center of Neptune is 7 Mbar or 700 Gpa.