Neptune is one of the outer planets and the farthest from the sun. It is thirty times farther from the sun than Earth. Neptune was the last planet to be discovered. This happened in 1846. Astronomers John Couch Adams and Urbain Jean Joseph LeVerrier thought that something was affecting the orbit of the planet Uranus. They tried to determine where that object might be. After a search, they discovered Neptune.
Neptune has no solid surface and is called a gas giant because it is mainly made up of gases. It consists mainly of water, ammonia, and methane. Neptune's atmosphere consists of hydrogen and helium. The planet has a blue color because the methane gas absorbs red wavelengths in sunlight, so the planet is named after the Roman god of the sea. Scientists believe that its center is a molten core of iron.
Since the planet takes 165 years to orbit the sun, it has only finished one orbit since its discovery. It has seasons, like Earth. However, a season lasts about forty years. A day on Neptune is sixteen hours and seven minutes. That means it rotates on its axis more quickly than Earth does. Earth's day is twenty-four hours.
Neptune's core is hotter than the surface of the sun, but the temperature at the top of the cloud layer is -350 F. Its weather is very fierce with winds blowing at more than 1,200 miles per hour. Dark spots which appear on the planet are storms. Its average distance from the sun is 2.8 billion miles.
Neptune's moon called Triton was discovered just seventeen days after the planet. Triton was the son of Neptune. A second moon was discovered in 1949, over a hundred years later. It was named Nereid. The Nereids were the sea nymphs of Greek mythology. Nereid travels almost 6,000,000 miles from its planet at its farthest point. It completes one orbit of the planet in about one Earth year.
Nereid was the only other moon besides Triton discovered before the Voyager 2 exploration. In 1989, the spacecraft Voyager found six other moons. Five of these were one hundred miles wide or smaller. Triton is more than 30,000 miles wide, obviously the largest moon. The latest moon, or the fourteenth, was discovered in 2013 by the Hubble Space Telescope. It is called S/2004 N1.
Triton is about three-quarters the size of Earth's moon. It is a ball of rock and ice. Its surface temperature is -391 F, one of the lowest in the solar system. It orbits its planet in less than six days. Near its south pole, pink methane ice can be seen. Although it is very cold, volcanic activity occurs. Ice bursts through cracks in the surface. The ice is made of nitrogen and turns to gas when heated by the sun.
Triton orbits in the opposite direction from the planet. It is a clockwise orbit. Because it goes in an opposite direction, it is called a retrograde orbit. It is the largest moon in the solar system which does this. This retrograde orbit will probably mean that in the future Triton will come too close to the planet, and the gravitational pull of Neptune will break the moon apart.
Proteus is another of Neptune's moons. It is larger than Nereid but was not discovered from Earth because it is so close to Neptune that the glare from the sunlight reflecting off the planet hid it. Proteus orbits the planet every twenty-seven hours. In 1981, scientists found a system of rings around Neptune by calculating the reduction in a star's light after Neptune had passed by the star. Therefore, Voyager's travel plans were changed so that the spacecraft could explore these rings.
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