The Neptune is the fourth largest planet in solar system and eighth planet from the Sun. The Neptune is third most massive and densest giant planet. It is the farthest from the Sun in solar system. The Neptune is not visible by unaided eyes. The Neptune is the only planet in solar system which was discovered by mathematical prediction.
Properties of Neptune
- The Neptune was discovered on 23 September 1846 by Urbain Le Verrier and Johann Galle.
- The Neptune was named upon Roman god of sea.
- The Neptune has the equatorial diameter is 49,528 km.
- Mass of the Neptune is 1.02 X 1026 kg which is 17 times that of the Earth.
- The Neptune has 14 moons and 5 rings.
- The Triton is the largest moon of the Neptune.
- One year on Neptune is equal to 164.79 Earth’s Years.
- The Surface temperature of the Neptune is -201oC.
- The gravity of Neptune is 11.15 m/s2which is 1.14 times that of the earth.
- Pressure in centre of core is 7 Mbar which is twice of the Earth.
- Temperature in centre of the core is 5100oC.
- Average distance of the Neptune from the sun is 4.5 billion km.
- Inclination of elliptical orbital plane of Neptune is 1.77o to the plane of Earth.
- Axial tilt of Neptune is 28.32o which causes the seasonal changes.
- One day on Neptune is 16.11 hours.
- Each season on Neptune is about of 40 years.
- The Neptune receives 40% of the sun light.
- The magnetic field of Neptune is 47o tilted by its axis of rotation and it is 27 times stronger than Earth’s magnetic field.
The concept of formation of Neptune is that it was formed nearer to the sun from solar nebula as rest of planets were formed, but due to higher matter density it was migrated to its current position in outer solar system.
Internal structure of the Neptune is similar to the Uranus. The outer layer of Neptune is composed of 5% to 10% of its mass and it is extends up to 10 % to 20 % towards the Core Where 10 GPa pressure is exist. The concentration of methane, ammonia and water is increasing toward the centre.
The Mantle is the rich icy mixture of water, ammonia and methane though it is hot and dense which is called water-ammonia Ocean with high electrical conductivity. At about 7000 km depth, the methane decomposes into diamonds crystals. The centre of the Neptune is solid Core made of iron, nickel and silicone with mass about 1.2 times of Earth. Pressure in the centre of core is about 7Mbar which is twice that of the centre of the Earth while temperature in centre of core is 5100oC.
Orbit and Rotation
The Neptune rotates around the Sun in elliptical path with closest distance (Perihelion) is 4.45 km while farthest distance (Apihelion) is 4.55 billion km. The Neptune completes one revolution around the sun in 164.79 years.
The elliptical orbital plane of Neptune is inclined by 1.77o to that of elliptical plane of the earth and axial tilt of Neptune is 28.32o. This inclination is nearer to the earth’s inclination so, seasons are experienced on Neptune but due to long orbital period every season is of about 40 years. The Neptune spins on its axis in 16.11 hours so, one day on Neptune is of 16.11 hours. The Neptune has no solid surface. The equatorial zones rotate in 18 hours while polar zones rotate in 12 hours.
The atmosphere of the Neptune is made of 80% of hydrogen and 19% of helium and also some amount of methane. The atmosphere of the Neptune is made of two layers. One is Troposphere and other is Stratosphere. Two layers are separated by Tropopause.
The lower most layer of the atmosphere of Neptune is Troposphere in which as the attitude increases the temperature decreases. The clouds composition in troposphere is depended on attitude. The upper level clouds are situated at the pressure below one bar and temperature in this zone is sufficient to condense the Methane. In pressure zone of 1 bar to 5 bar, ammonia and hydrogen sulfide’s clouds are formed. Above 5 bar, the clouds are made of ammonia, ammonium sulphide, hydrogen sulphide and water. At 50 bar pressure, water ice clouds are found where temperature is about 0oC.
The outer layer above the Troposphere is called Stratosphere in which the temperature is gradually increased with attitude. This layer is made of ethane and acetylene with trace amount of carbon monoxide and hydrogen cyanide. The stratosphere of Neptune is warmer than that of the Uranus.
Amount of methane, ethane and acetylene at equator is 10 to 100 times more than that on poles. The South Pole is 10K hotter than rest of the atmosphere of Neptune. The Neptune is moving opposite direction to the sun at slow rate and so the North Pole will be darkened and South Pole will be lightened. The atmosphere of Neptune is experienced various strong storms having wind speed about 600m/s and the direction of winds is opposite to the rotation of the Neptune. The wind speed at the equator is 400m/s while at the pole is 250 m/s.
Great Dark Spot
The Great Dark Spot is known as GDS-89 was discovered in 1989 a series of dark spot similar to Great red spot on Jupiter and also anti cyclonic storms. The size of this spot was 13000km length and 6600 km width which is about the size of the Earth. The wind speed in spot is about 1300 m/h which is fastest in entire solar system. The size and shape of spot is vary time to time. The great dark spot on Neptune creates white clouds which are made of crystals of frozen methane. These remain for several months.
The magnetic field of the Neptune is tilted by 47o from the axis of rotation. It is also offset by 0.55 radius or about 13500 km from centre of Neptune. This inclination is due to the properties of flows in interior of the planet. The magnetic field of Neptune is 27 times stronger than Earth.
Rings of Neptune
The Neptune has five main rings which were discovered on July 22 1984. Galle, Le Verrier, Lassell, Arago and Adams are names of the five main rings. The rings of the Neptune are made of large quantity of micrometer sized dust and dark material which is mixture of ice and radiation processed organics. The rings are reddish in colour.
Galle Ring is the inner most ring which was discovered by Johann Gottfried Galle. This ring is 2000km wide and lies at 41000km to 43000 km from planet. The equivalent depth of ring is 0.15 km and dust fraction is 40 % to 70%.
Le Verrier Ring is the next second ring was discovered by Urbain Le Verrier. This is narrow ring having 113 km width with orbital radius is 53200 km and thickness is about 0.7 km. The Despina moon orbits inside this ring.The dust fraction is about 40% to 70%.
Lassell Ring is third inner ring which is known as plateau was discovered by William Lassell. This ring is broadest ring of Neptune which lies at 53200 km to 57200 km. Its equivalent depth is 0.4 km and dust fraction is about 20% to 40%.
Arago Ring is located at 57200 km and about 100 km wide was discovered by Francois Arago.
The Outer Adams Ring was discovered by John Couch Adams. This is narrow ring about 35 km and located at about 63930 km with equivalent depth is 0.4 km. the dust fraction is about 20% to 40%. Gelatea moon orbits inside this ring which is the main source of particles of rings. The arcs are the brightest part of the Adams ring system. The Adams ring has five arcs.
Moons of Neptune
The Neptune has 14 natural satellites or moons which all are named for water deities in Greek Mythology. The moons of Neptune are classified into two groups. One is regular moons which cover seven moons orbit in circular prograde path in equatorial plane of Neptune. Second is irregular moons which cover other seven moons orbit inclined and eccentric retrograde path.
The regular moons are made of water ice with some dark material complex organic compounds. Naiad, Thalassa, Despina, Galatea, Larissa, Hippocamp and Proteus are the regular moons of Neptune in order the distance from the planet. All inner moons are associated with the ring system of Neptune. Naiad and Thalassa orbit between Galle and Le Verrier rings. Despina orbits inside the Le Verrier ring which provides material for ring. The Galtea orbits inside the Adams ring.
Triton, Nereid, Halimede, sao, Laomedeia, Psamathe and Neso are the irregular moons of Neptune in order the distance from the planet. The Triton is the biggest moon of Neptune which was discovered 17 days after discovery of Neptune. The Triton orbits retrograde to rotation of Neptune and also inclined to equator of Neptune. The Triton and the Nereid are the biggest irregular moons of solar system.
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Authored by BK Suthar.
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