5.9. Planets of the Solar System: Neptune
Neptune, the farthest planet from the Sun in our solar system, is an intriguing and mysterious gas giant. Named after the Roman god of the sea, this blue-green planet is the fourth largest in terms of diameter and third largest in terms of mass. Neptune's average distance from the Sun is about 4.5 billion kilometers, and its atmosphere composed mainly of hydrogen and helium, with traces of methane, gives the planet its distinctive blue color.
Neptune was the first planet to be discovered through mathematical predictions. In 1846, Johann Gottfried Galle and Heinrich Louis d'Arrest, two German astronomers, discovered Neptune just 1° away from the predicted position. The discovery of Neptune was seen as a triumphant confirmation of Newton's law of gravity.
Physical Characteristics and Atmosphere of Neptune
Neptune is known for its strong winds, some of the fastest in the solar system, reaching 2,100 kilometers per hour. These winds are powered by the planet's internal energy rather than heat from the Sun, which is very weak at that distance. The planet also has a strong magnetic field, tilted at 47 degrees to the axis of rotation.
Neptune's atmosphere is made up of a small amount of methane, which absorbs red light and reflects blue light from the Sun, giving the planet its bluish color. The upper atmosphere contains thin clouds of methane crystals, while lower down, pressure and temperature increase, compressing the gas into an ocean of hydrogen, helium and traces of liquid methane.
Neptune's Moon System
Neptune has 14 known moons. The largest of these, Triton, is the only moon in the solar system that orbits in the opposite direction to the planet's rotation, a phenomenon known as retrograde orbit. Triton is extremely cold, with surface temperatures reaching -235 degrees Celsius, making it one of the coldest moons in the solar system. Triton is believed to be a Kuiper Belt object captured by Neptune's gravity.
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The Orbit and Rotation of Neptune
Neptune takes 165 Earth years to complete one orbit around the Sun. This means that since its discovery in 1846, Neptune only completed one orbit in 2011. The planet has a rapid rotation, with a day on Neptune lasting about 16 hours.
Neptune Exploration
The only space probe to visit Neptune was NASA's Voyager 2, which performed a flyby in 1989. Voyager 2 discovered six of Neptune's moons, as well as a faint ring system and four main rings. The probe also observed Neptune's Great Dark Spot, a giant storm similar to Jupiter's Great Red Spot, which has since disappeared.
Despite its distance from the Sun, Neptune continues to be an object of fascination and study for astronomers and scientists. Its composition, atmosphere, and system of moons offer many opportunities for future exploration and discovery.
