Neptune

                             Neptune 

Neptune is the last and the farthest planet from the Sun at a distance of about 4,500 million kilometres. The bright blue atmosphere is cold and contains hydrogen, helium, and methane. The bluish appearance of this planet has given it the name of the Roman God of the sea. Neptune's ocean is extremely hot with about 4700°C. But it remains liquid instead of evaporating because the pressure in Neptune is several million times higher than the atmospheric pressure on Earth. The increased pressure holds the molecules in liquid closer together and prevents them from scattering to form vapour. A mantle of ammonia, methane and icy water covers the rocky silicate core. Huge storms swirl around the planet at a speed of about 2000 kilometres per hour. The Great Dark Spot and the Small Dark Spot are the largest. Four narrow rings encircle Neptune. The planet has eight satellites. Triton the coldest object in the Solar System with -235°C temperature is the largest satellite of Neptune. Unlike other satellites it orbits in the opposite direction of Neptune's rotation. Neptune completes one rotation in 16 hours 7 minutes and it takes 165 years to complete one revolution.

                    Rings of Neptune

Neptune has four narrow rings. The outermost ring has an unusual feature among planetary rings. It is faint with three curved and bright segments. The Neptunian rings are thickly filled with dust particles. They are visible only when backlighted by sunlight.

            Cloud features of Neptune

The atmosphere of Neptune contains numerous important cloud features. The Great Dark Spot, the Small Dark Spot and the Scooter are the largest among them. The Great Dark Spot and the Small Dark Spot are huge storms that blow at a speed of about 2000 kilometres per hour. A large area of cirrus cloud is called the Scooter.

                 A flight to Neptune

As Neptune is the farthest planet from the Earth only one spacecraft has been sent to this planet. The probe Voyager 2 launched on August 1977 visited Neptune in 1989 after passing Jupiter, Saturn and Uranus. Voyager 2 collected details of Neptune's rings and satellites. Six new satellites of this planet have been discovered by Voyager 2. The largest among them is only 180 kilometres in diameter (about the same size of a crater in the moon).

                           Neptune

Distance from the sun in km.: 4504.3 million

Diameter at equator in km.: 49100

Mass with respect to the earth: 17.15

(earth=1)

Gravity with respect to the earth: 1.14

Period of revolution: 165 earth years

Period of rotation: 16 hours and 7 minutes

Density (g/cm³): 1.64

Temperature:-214°C

Satellites: 8